Full text of DOI:10.1007/BF03345110

J. Endocrinol. Invest. 25: 735-747, 2002
REVIEW ARTICLE
Benzodiazepines and anterior pituitary function
E. Arvat, R. Giordano, S. Grottoli, and E. Ghigo
Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Turin, Turin, Italy
ABSTRACT. Benzodiazepines (BDZ) are one of the
most prescribed classes of drugs because of their
marked anxiolytic, anticonvulsant, muscle relaxant
and hypnotic effects. The pharmacological actions
of BDZ depend on the activation of 2 specific re-
ceptors. The central BDZ receptor, present in sev-
eral areas of the central nervous system (CNS), is
a component of the GABA-A receptor, the activa-
tion of which increases GABAergic neurotrans-
mission and is followed by remarkable neuroen-
docrine effects. The peripheral benzodiazepine re-
ceptors (PBR), structurally and functionally differ-
ent from the GABA-A receptor, have been shown
in peripheral tissues but also in the CNS, in both
neurones and glial cells, and in the pituitary gland.
BDZ receptors bind to a family of natural peptides
called endozepines, firstly isolated from neurons
and glial cells in the brain and then in several pe-
ripheral tissues as well. Endozepines modulate sev-
eral central and peripheral biological activities, in-
cluding some neuroendocrine functions and syn-
thetic BDZ are likely to mimic them, at least par-
tially. BZD, especially alprazolam (AL), possess a
clear inhibitory influence on the activity of the HPA
axis in both animals and humans. This effect seems
to be mediated at the hypothalamic and/or supra-
hypothalamic level via suppression of CRH. The
strong negative influence of AL on hypothalamic-
pituitary-adrenal (HPA) axis agrees with its peculiar
efficacy in the treatment of panic disorders and
depression. BZD have also been shown to increase
GH secretion via mechanisms mediated at the hy-
pothalamic or supra-hypothalamic level, though a
pituitary action cannot be ruled out. Besides the
impact on HPA and somatotrope function, BDZ al-
so significantly affect the secretion of other pitu-
itary hormones, such as gonadotropins and PRL,
probably acting through GABAergic mediation in
the hypothalamus and/or in the pituitary gland. In
all, BDZ are likely to represent a useful tool to in-
vestigate GABAergic activity and clarify its role in
the neuroendocrine control of anterior pituitary
function; their usefulness probably overrides what
had been supposed before.
(J. Endocrinol. Invest. 25: 735-747, 2002)
©2002, Editrice Kurtis
INTRODUCTION
GABAergic neurotransmission (4, 5), which plays
the most important inhibitory influence in the CNS
(1). Moreover, GABA has been found to modulate
pituitary function by acting at the hypothalamic lev-
el where influences hypophysiotropic neurohor-
mone release, and/or directly on the pituitary gland,
where different GABA receptor subtypes have been
detected (6-13).
There is evidence that clinical actions of BDZ are
mainly mediated by inhibitory influence on 3 classi-
cal stress systems: sympatoneural and adreno-
medullary systems and hypothalamic-pituitary-
adrenal (HPA) axis. BDZ-induced GABAergic activa-
tion counteracts HPA hyperactivation associated to
stressful conditions and there is evidence that CRH
per se increases vigilance, attention, anxiogenic be-
havior and reduces feeding and hypothalamic-pitu-
itary-gonadal activity (1, 14-17). Moreover, alterations
in the balance of central activating and inhibiting
Benzodiazepines (BDZ) are one of the most pre-
scribed classes of drugs because of their marked
anxiolytic, anticonvulsant, muscle relaxant and hyp-
notic effects (1). It has been shown that many of the
pharmacological actions of BDZ are mediated by
specific binding sites, distributed not only in the
central nervous system (CNS) but also in peripher-
al tissues. In the CNS BDZ bind a specific BDZ bind-
ing site which is a component of the GABA-A re-
ceptor (1-3). This receptor activation facilitates brain
Key-words: Benzodiazepines, ACTH, GH, gonadotropins, PRL, TSH.
Correspondence: Prof. Emanuela Arvat, MD, Divisione di Endocrinologia
e Malattie Metaboliche, Dipartimento di Medicina Interna, C.so Dogliotti
14, 10126 Torino.
E-mail: e.arvat@libero.it
Accepted March 19, 2002.
735

E. Arvat, R. Giordano, S. Grottoli, et al.
neurotransmission might be involved in the patho-
physiology of some psychiatric disorders, such as
major depression or panic disorders (18-20). Among
BDZ alprazolam (AL), a triazolobenzodiazepine with
peculiar efficacy in the treatment of panic disorders
and depression (21-23), possesses the most remark-
able inhibitory influence on ACTH and F release (see
below for references).
Besides the impact on HPA axis, BDZ also signifi-
cantly affect the secretion of other pituitary hor-
mones, particularly GH, gonadotropins and PRL,
probably acting through GABAergic mediation in
the hypothalamus and/or in the pituitary gland (see
below for references).
GABA-A receptor, a macromolecular complex with
separate binding sites for GABA, BDZ and barbitu-
rate-like substances (1-3). Activation of GABA-A-
binding sites induces the opening of the chloride
ionophore linked to GABA-A receptors, leading to
membrane hyperpolarization and to inhibition of
cell firing (28). There is evidence that BDZ binding
to GABA-A receptor complex enhances GABA
binding to its receptor site, thus increasing the ac-
tivity of the GABAergic system (4, 5), which is the
major inhibitory system in the brain. GABA, GABA-
mimetic compounds and barbiturates increase the
affinity of BDZ to their receptors, suggesting strict
anatomical and functional link between BDZ and
GABAergic pathways (1).
On the other hand, a different class of BDZ recep-
tor named “peripheral benzodiazepine receptors”
(PBR) has been shown in peripheral tissues but also
in the CNS, in both neurones and glial cells (24, 25).
The activation of these receptors plays a critical role
in steroidogenetic processes leading to the syn-
thesis of both neurosteroids and steroid hormones
in peripheral glands (24, 25). PBR activation might
play also some modulatory influence on the activi-
ty of the anterior pituitary gland (24, 25). It has to be
emphasized that BDZ receptors including PBR bind
a family of natural peptides called “endozepines”.
An 86-amino-acid polypeptide, named diazepam-
binding inhibitor (DBI), was the first “endozepine”
isolated from neurons and glial cells in the rat brain
and then detected in several peripheral tissues too
(24, 25). This and other related endozepines char-
acterized thereafter modulate several central and
peripheral biological activities, including some neu-
roendocrine functions (24-26). Thus, the neuroen-
docrine effects of BDZ are likely to reflect neu-
roendocrine actions of natural endozepines.
Three classes of ligands have been demonstrated
to bind central BDZ receptor sites: agonists, which
show anxiolytic and anticonvulsant effects, antag-
onists, which have no intrinsic pharmacological ac-
tivity but block the actions of BDZ agonists, and in-
verse agonists, which show an intrinsic proconvul-
sant effect in animals (1, 29-31).
The actions of GABA/BDZ on the anterior pituitary
function are believed to be mainly mediated at the
hypothalamic level, where a great amount of neural
connections between GABAergic pathways and neu-
rons releasing hypophysiotropic neurohormones
have been demonstrated (6-8). On the other hand,
GABA is released in the hypothalamo-hypophyseal
portal circulation from neurons located in the medi-
an eminence and, thus, can directly act on pituitary
cells through specific GABA receptors, including GA-
BA-A subtypes (11, 32-35). Thus, this evidence indi-
cates the existence of a direct pituitary action of BDZ
to modulate anterior pituitary function.
The peripheral type of BDZ receptor is a different
class of binding sites for BDZ, located on the outer
mitochondrial membrane, not functionally linked to
the GABA regulated chloride channel and showing
different selectivity to ligands (24, 25). PBR are pre-
sent in high concentrations in steroid-producing tis-
sues, such as adrenal cortex, testis, ovary, in the
kidney and also in brain glial cells, hypothalamus
and pituitary (24, 25, 36). In both peripheral tissues
and brain these receptors play a crucial role in the
regulation of steroidogenesis: they control the first
step of the steroid biosynthetic pathway, i.e. the
cholesterol delivery from the outer to the inner mi-
tochondrial membrane (24, 25).
PBR were found as the first target of natural ligands
called endozepines. The endozepine family is de-
rived from a brain polipeptide, named DBI, which
was discovered as the first endogenous ligand for
PBR though it also binds to the GABA/BDZ receptor
complex (1, 24-26). DBI was isolated from rat brain
Based on the foregoing, this paper aims to review
the present knowledge regarding the effects of
BDZ on anterior pituitary function, with particular
focus on data so far available in humans, in both
physiological and physiopathological conditions.
FUNDAMENTALS IN BDZ
The pharmacological actions of BDZ depend on ac-
tivation of their specific receptors. Two types of spe-
cific BDZ binding sites have so far been discovered:
central and peripheral receptors (1, 24). High-affin-
ity, saturable and stereospecific central binding sites
for BDZ have been demonstrated in the cerebral
cortex, cerebellum, hippocampus, amigdala, locus
coeruleus and medial hypothalamus, but also at pi-
tuitary level, both in the anterior and posterior lobe
(1, 27).
The central BDZ receptor is a component of the
736

Benzodiazepines and pituitary function
and, later, from bovine and human brain, in both
neurones and glial cell, where PBR as well as classi-
cal BDZ receptors are also present (25). The prima-
ry structure of DBI has been shown to be well con-
served during evolution, suggesting that this pep-
tide plays important biological functions (37). DBI
and other endozepines have also been found in sev-
eral peripheral tissues, particularly in the adrenal cor-
tex, testis and ovary, where they are deeply involved
in the control of steroidogenesis (25). The activation
of PBR by endozepines in glial cells induces the syn-
thesis of neurosteroids, which, in turn, modulate
neuronal activity and brain function through the
modulation of GABA/BDZ receptors which, as an-
ticipated, are bound by endozepines (25).
The evidence that GABAergic pathways are pre-
sent in high density in the hypothalamus and me-
dian eminence (34, 35) coupled with the demon-
stration of both GABA/BDZ and PBR in the pituitary
gland (11, 32-35, 38, 39) suggested a role for en-
dozepines as well as for BDZ in the modulation of
the anterior pituitary function.
but also in the treatment of panic disorders and de-
pressive disorders, in which a central HPA hyper-
activation has been demonstrated (20-23).
AL shows a very high affinity for central BDZ re-
ceptors and a short elimination half-life (10-15 h),
associated with small amounts of active metabo-
lites, which are rapidly excreted in the urine (55-57).
AL has been shown to significantly reduce basal
corticotrope and adrenal secretion as well as the
ACTH response to insulin-induced hypoglicemia in
animals (58-60). Moreover, in vitro studies showed
that basal and serotonin-stimulated CRH secretion
was inhibited by AL in locus coeruleus and hypo-
thalamus, with a potency 40 times higher than dia-
zepam (58, 60).
In agreement with data in animals, in human studies
AL has been demonstrated to significantly decrease
urinary free F as well as circulating ACTH/F levels, en-
hancing the spontaneous decline of HPA activity in
the morning hours, indicating a clear influence of BDZ
on the basal HPA activity (20, 61). On the other hand,
AL has been shown to significantly blunt the ACTH
and/or F response to several stimulations, such as
metabolic, mental stress, naloxone and AVP (62-67),
while it totally abolished the ACTH response to
hexarelin, a synthetic growth-hormone-releasing-pep-
tide (GHRP) with ACTH-releasing effect (68). More-
over, AL did show a marked inhibitory effect even on
ACTH rise induced by metyrapone or insulin-induced
hypoglycemia, the most potent stimulations of corti-
cotrope secretion (61, 69), clearly indicating a prima-
ry role of BDZ in the modulation of corticotrope func-
tion. Evidence that AL possesses a more marked in-
hibitory effect on HPA axis than other BDZ indicates
the peculiar activity of this BDZ possibly reflecting its
higher affinity for GABA/BDZ binding sites (70).
There is clear evidence that BDZ act through the
modulation of GABAergic neurotransmission in
both animals and humans (see previous pages for
references) and that GABAergic pathways are in-
volved in the neural control of HPA axis. In fact, AL
as well as diazepam, although with a lesser poten-
cy, are able to suppress CRH secretion in the hypo-
thalamus and locus coeruleus while neither AL nor
GABA modified basal or CRH-stimulated ACTH re-
lease from pituitary cells (58, 60). Thus, the in-
hibitory action of BDZ/GABA on HPA axis mainly
takes place at hypothalamic and/or suprahypotha-
lamic level via suppression of CRH. Accordingly, re-
cent studies showed that GABA and GABA-A ago-
nists negatively influence CRH gene expression in
the rat hypothalamus and that this effect is reversed
by antagonists of GABA/BDZ binding sites (9, 71).
On the other hand, other data indicated an AVP-
mediated mechanism of GABA/BDZ on HPA axis. In
Besides the regulation of brain and peripheral
steroid synthesis, it has been demonstrated that
endozepines exert other remarkable activities, such
as modulation of melanotropin release from pitu-
itary cells, inhibition of insulin secretion from the
pancreas, stimulation of intestinal cholecystokinin
and regulation of cellular growth and differentia-
tion (37).
BDZ AND HYPOTHALAMIC-PITUITARY-
ADRENAL AXIS
It has been clearly demonstrated that BDZ admin-
istration affects the activity of the HPA axis.
The first studies, generally obtained studying the
effects of diazepam, reported conflicting results in
both animals and humans. An inhibitory effect of
diazepam on ACTH, corticosterone/F release was
reported by some (40-43) but not by other Authors
(44) in animal studies. Significant inhibitory effect
of diazepam on HPA was found by some Authors
in humans too (45-48), while others did not show
any significant effect (49, 50). Moreover, other BDZ,
such as oxazepam, triazolam or flurazepam, showed
negligible or no effect on corticotrope and adrenal
function in normal subjects (51, 52).
Clear evidence of the inhibitory effect of BDZ on
HPA axis came from the studies using AL, a tria-
zolobenzodiazepine which mainly acts as an ago-
nist of the GABA/BDZ receptor complex (53-55).
AL possesses the most remarkable inhibitory effect
on HPA axis and this peculiar activity seems to ex-
plain its clinically efficacy not only as anxiolitic agent
737

E. Arvat, R. Giordano, S. Grottoli, et al.
AL
fact, GABA is synthesized in both supraoptic and
paraventricular nuclei, where AVP is produced (72);
moreover, GABAergic compounds reduce circulat-
ing AVP levels and inhibit AVP release from the hy-
pothalamus and posterior pituitary in rats (73-75).
Evidence in humans that AL is able to inhibit the
ACTH and F response to CRH-mediated stimuli, such
as naloxone or metyrapone, to AVP but not to CRH
(61-67, 76) (Fig. 1) reinforces the hypothesis that BDZ
are likely to act within the CNS via inhibition of CRH
release. However, other studies indicate that BDZ
could act via AVP-mediated mechanisms (76-78), al-
though some Authors did not find any significant ef-
fect of AL on AVP release in humans (63).
It has also been proposed that BDZ and GABA may
influence HPA axis by acting at suprahypothalamic
level. AL pre-treatment significantly decreases hip-
pocampal CRH receptors in rats (79). Moreover, in
humans, it abolishes the nocturnal ACTH and F rise
induced by potassium canrenoate, an antagonist of
both peripheral and hippocampal mineralocorticoid
receptors (MR) (80). As the hippocampal MR acti-
vation is deeply involved in the glucocorticoid-me-
diated negative feed back mechanism (81), these
results indicated the involvement of BDZ in the
modulation of the negative feed-back mechanism
induced by glucocorticoids. This is in agreement
with the ability of AL to inhibit the stimulatory ef-
fect of the metyrapone-induced removal of corti-
costeroid feed back on corticotrope secretion (61).
Several studies showed that high BDZ doses reduce
baseline and stress-induced NE turnover (82, 83).
Moreover, BDZ have been found to inhibit cell firing
and noradrenergic activity in the locus coeruleus,
which provides central noradrenergic inputs to the
CRH neurons, while GABA/BDZ receptors have been
demonstrated on presynaptic axons and nerve ter-
minals of noradrenergic neurons located in cerebral
cortex and hippocampus (84-86). Thus, it has been
hypothesized that BDZ may indirectly influence HPA
activity via modulation of noradrenergic function. In
agreement with this hypothesis, in humans the ad-
ministration BDZ, namely AL, is followed by decrease
in NE and/or NE metabolite levels (62, 63, 87).
Moreover, AL antagonizes the behavioral and neu-
roendocrine effects of yohimbine and viceversa sug-
gesting that the BDZ action on noradrenergic func-
tion could be mediated by the α2-adrenergic modu-
lation (87).
400
300
200
100
0
MET
MET+AL
MET
23:00
MET
07:00
AL
08:00
08:00
08:00
09:00
10:00
11:00
12:00
12:00
12:00
Time (h)
200
150
100
50
0
23:00
MET
07:00
AL
09:00
10:00
11:00
Time (h)
120
90
60
30
0
23:00
07:00
09:00
10:00
11:00
Time (h)
Fig. 1 - Mean ( SE) ACTH, 11-desoxycortisol (S) and F levels af-
ter metyrapone (MET, 0.04 g/kg, orally, at 23:00 h the night be-
fore) alone and combined with alprazolam (AL, 0.02 mg/kg,
orally, at 07:00 h) in normal subjects.
As far as the influence of PBR on the activity of HPA
axis is concerned, their localization in CNS, pituitary
and adrenal gland suggested an action of these re-
ceptors at different levels. PBR agonists have been
shown to increase CRH and ACTH release from rat
hypothalamus and pituitary, respectively (38), sug-
Finally, although BDZ failed to modify CRH-induced
ACTH secretion from rat pituitary (58), the existence
of GABA/BDZ receptors in the pituitary gland (88)
suggested a direct modulatory role of GABA and/or
BDZ on corticotrope secretion induced by ACTH
secretagogues other than CRH.
738

Benzodiazepines and pituitary function
Table 1 - Influence of benzodiazepine (BDZ) receptors on anterior pituitary hormones.
GABA/BDZ receptors
PB receptors
ACTH
GH
↓ (20-23, 40-48, 58-69, 71, 73-79, 80, 89)
↑ (24, 25, 38)
= (49-52)
↑ (32, 62, 63, 90-94, 101-104, 108, 111, 136)
↓ (68, 100, 105, 106)
= (95-99, 135)
↑ (39)
Gonadotropins
PRL
↓ (26, 117-121)
↓ (108)
↓ (127)
↑ (59, 88, 108, 122)
↑ (62, 126, 136)
↓ (127-130)
= (116,125,135)
TSH
= (32, 102, 127, 130, 137)
↓ (109)
No data available
↓ inhibitory effect, ↑ stimulatory effect, =no effect. Notice: GABA/BDZ receptors are the central BDZ receptors; PB receptors are peripheral BDZ receptors
(PBR) that have been shown also in the central nervous system.
gesting a peculiar stimulatory role of PBR in the
modulation of HPA axis. On the other hand, al-
though PBR activation stimulates steroidogenesis
in the adrenal gland, some studies showed an in-
hibitory effect of diazepam on ACTH-induced
steroidogenesis in animals (24). In agreement with
this hypothesis, we have demonstrated that AL sig-
nificantly blunts the adrenal response to low ACTH
doses in humans (76). However, it is noteworthy
that endozepines play a key role in the stimulation
of steroidogenesis in the adrenal gland by activat-
ing PBR (24, 25). Based on this evidence, it has
been hypothesized that DBI may be involved in the
long-term trophic effect of ACTH on adrenal gland
though it unlikely mediates the short-term adrenal
response to ACTH (25). Taken all together, these
data show how complex are effects of PBR activa-
tion on HPA axis and suggest that their activation
has different effects depending on different recep-
tor localization and/or different ligands.
From a clinical point of view, it is well known the pe-
culiar efficacy of AL in the management of panic dis-
orders and depression, probably due to its marked
inhibiting effect on HPA axis (21-23). On the other
hand, it has to be pointed out that BDZ may be a use-
ful tool to investigate GABAergic as well as HPA ac-
tivity in some pathophysiological conditions. To this
regard, it has been demonstrated that BDZ do not
modify ACTH hypersecretion in patients with Cu-
shing’s disease (77, 89), suggesting that GABA is un-
able to influence corticotrope secretion in this con-
dition. Moreover, we have previously shown that AL
possesses a less potent blunting effect on ACTH and
F response to hexarelin in obesity than in normal sub-
jects (89), suggesting that the inhibitory influence of
BDZ/GABA on the ACTH-releasing activity of GH sec-
retagogues is impaired in obesity.
Finally, the data above reported clearly indicate
that the effects of BDZ on HPA function should be
taken in account when endocrinological assessment
is performed in patients with suspected impaired
HPA activity; moreover, when BDZ treatment has
to be started in patients with anxiogenic disorders,
caution in the use of these drugs, especially AL,
should used in those patients with suspected hy-
poadrenalism (Table 1).
BDZ AND SOMATOTROPE FUNCTION
The first studies focusing on the activity of BDZ on
GH secretion reported controversial results. Diaze-
pam had been reported to significantly increase GH
release in normal subjects in a dose-dependent man-
ner (90-92) and similar results were found using oth-
er BDZ molecules (93). Moreover, evidence that
flumazenil, an inverse agonist of the GABA/BDZ
binding site, significantly inhibited nocturnal GH re-
lease suggested a tonic stimulatory influence of GA-
BA/BDZ on GH secretion (94).
Other Authors failed to confirm a positive effect of
BDZ on somatotrope function; neither diazepam af-
fected either morning or nocturnal spontaneous GH
release and nor BDZ, such as triazolam, flurazepam
or bretanezil had any significant effect (95-99). Even
an inhibitory effect of BDZ on somatotrope secre-
tion was reported after administration of the BDZ
agonist midazolam (100). As marked inter-subject
variability in the GH response to BDZ has been
found (101, 102), this could probably explain the
controversial data reported above.
Clear stimulatory effect of BDZ on GH secretion
has been demonstrated in the studies addressing
the effects of AL. In fact, it clearly increases GH se-
cretion in both rats and humans, showing in the
739

E. Arvat, R. Giordano, S. Grottoli, et al.
latter dose-related effect (62, 63, 103, 104). When
evaluated in equipotent doses in rats, AL showed
higher GH-releasing effect than diazepam, once
again indicating the peculiarity of this benzodi-
azepine (104).
pothalamic level. This hypothesis based on the ev-
idence that central BDZ receptor ligands show little
or no effect on GH release in both normal and tu-
moral rat somatotroph cells in vitro (39, 109) and
that BDZ treatment does not modify the GH re-
sponse to GHRH in either normal subjects or pa-
tients with panic disorder (110).
Although BDZ possess per se stimulatory effect on
spontaneous GH secretion, it is remarkable that
they are paradoxically able to blunt GH response
to some provocative stimuli. AL, in fact, blunts the
GH response to hexarelin, a synthetic GH secreta-
gogue (68) as well as to meta-chlorophenylpipera-
zine, a serotonin receptor agonist (105) (Fig. 2).
Moreover, diazepam had been shown able to re-
duce the GH response to L-DOPA and apomor-
phine in normal subjects (106). The explanation of
the paradoxical effects of BDZ on somatotrope se-
cretion (stimulatory on spontaneous but inhibitory
on stimulated GH secretion) is still unclear but, any-
way, indicates a tight interplay between GABA/BDZ
and the major neural systems controlling soma-
totrope function. In agreement with this hypothesis,
it has also been demonstrated that GABA, which
positively influences spontaneous GH secretion,
blunts the GH responsiveness to insulin-induced
hypoglycemia (107).
As far as the mechanisms underlying the BDZ ef-
fects on GH secretion are concerned, it has been
shown that GABA antagonists are able to inhibit
GH response to BDZ while BDZ receptor antago-
nists are able to reverse the effects of both BDZ ag-
onists and inverse agonists on GH secretion (108).
Thus, this indicated that BDZ actually act through
GABA/BDZ receptor activation to modulate GH re-
lease.
AL-induced GH rise is blocked in rats by yohim-
bine and idazoxane, two α2 antagonists (104), sug-
gesting that the effect of this BDZ on GH release
could involve the α2 adrenoceptor activation, al-
though AL does not bind α2 receptors (63). A
dopaminergic mediation of BDZ effect on GH re-
lease has also been suggested, as the GH re-
sponse to diazepam is significantly reduced by
dopaminergic antagonists (111). Finally, the evi-
dence that both GABA and BDZ inhibited so-
matostatin release from some rat central areas in
vitro (112) led to hypothesize a somatostatin-me-
diated action of GABA/BDZ system in the modu-
lation of somatotrope function. However, against
this hypothesis is the evidence that neuroactive
substances acting via inhibition of somatostatin re-
lease show potentiating effect on GHRH-induced
GH rise (113), while BDZ do not demonstrated any
effect on this response in humans (110).
Although direct effect of BDZ on somatotrope cells
had not been found by some Authors (39,109), BDZ
agonists have been shown to be able to potentiate
the GH rise induced by GABA agonists in rat pitu-
itary (32), suggesting direct stimulatory modulation
of BDZ on GH release. Moreover, GABA im-
munoreactivity has been found in rat somatotrope
cells, suggesting an autocrine and/or paracrine ef-
fect of GABA on somatotrope function (114).
Interestingly, TRH-induced GH rise has been re-
ported to be inhibited by BDZ pretreatment in rat
pituitaries, as consequence of the competition for
pituitary TRH receptors (32, 115). This evidence in-
dicates that BDZ may also negatively modulate GH
release in the pituitary gland by acting on recep-
tors other than GABA/BDZ ones. In this context,
PBR seem involved in the BDZ modulation of so-
matotrope function at pituitary level; in fact, the ex-
posure of tumoral GH3 cells to a PBR agonist in-
creases GH secretion (39), suggesting a stimulato-
ry influence of these binding sites on GH secretion.
The possibility that the GH-releasing activity of BDZ
has some clinical impact seems very unlikely. From
the diagnostic point of view, the great intraindivid-
ual variability in the GH response to BDZ in normal
subjects strongly reduces their reliability as provo-
cative stimuli to evaluate the secretory capacity of
somatotrope cells in the suspect of GH deficiency
(101, 102, 116) (Table 1).
The influence of BDZ on GH secretion is likely to
be mediated at the hypothalamic and/or suprahy-
AL
100
80
60
40
20
0
HEX
AL+HEX
HEX
-90
0
30
60
90
120
Time (h)
Fig. 2 - Mean ( SE) GH responses to Hexarelin (HEX, 2.0 μg/kg
i.v. at 0 min) preceded by either placebo or alprazolam (AL,
0.02 mg/kg, orally, at -90 min) in normal subjects.
740

Benzodiazepines and pituitary function
BDZ AND GONADOTROPE, LACTOTROPE AND
THYROTROPE FUNCTION
Gonadotrope function
on gonadotropin secretion. It has been demonstrat-
ed that PBR activation is followed by the inhibition
of gonadotrope function in animals (108). On the
other hand, a modulatory role of GnRH, PRL and go-
nadal steroids on both central and peripheral BDZ
receptor expression has been found in different tis-
sues. In fact, hypothalamic, pituitary and adrenal PBR
expression is reduced during pregnancy and lacta-
tion in rats (123), as well as in platelets of pregnant
women (124), thus suggesting a negative influence of
hypothalamic-pituitary-gonadal axis as well as of PRL
on PBR function. On the contrary, the hormonal
changes occurring during pregnancy were found as-
sociated with an increase of PBR density in ovary and
uterus (123), suggesting a tissue-dependent effect
of the hypothalamic-gonadal axis on the expression
of these receptors. In agreement with this hypothe-
sis, BDZ receptor expression was increased in the
hippocampus but decreased in both hypothalamus
and pituitary during pregnancy in rats (123).
A BDZ influence on the activity of the hypothalam-
ic-pituitary-gonadal axis has been shown and it is
mainly mediated by GABA/BDZ receptor binding.
GABA plays a major role in the control of go-
nadotropin release, by acting at different levels.
Besides the extensive network of GABA-containing
fibers in the hypothalamus, which are likely to interact
with GnRH-secreting neurons, (34, 35), GABAergic
receptors have been demonstrated in the pituitary
gland, which probably mediate a direct influence of
GABA on gonadotrope cells (11, 88).
The activation of the GABA-A receptor complex by
GABA, GABA agonists, barbiturates as well as en-
dogenous and synthetic BDZ inhibits GnRH gene
expression in rat medial preoptic area (117-119)
and that this effect is completely antagonized by
GABA-A/BDZ antagonists (26, 117-119). Thus, GA-
BA/BDZ receptor activation is likely to exert a ton-
ic inhibitory influence on GnRH-secreting neurons.
On the other hand, direct effect of GABA on go-
nadotrope function has also been described (88).
The presence of either inhibitory or excitatory in-
fluence of GABA receptors on gonadotrope cells
has been shown; the activation of the latter ones
potentiates the effect of GnRH on the intracellular
mechanisms leading to gonadotropin secretion
(88). Thus, it has been hypothesized that the stim-
ulatory effect of BDZ/GABA on gonadotrope func-
tion may reflect a pituitary action while the in-
hibitory influence could reflect mediation by cen-
tral BDZ/GABA receptors (108).
In agreement with the hypothesis of a dual effect
of GABA/BDZ on gonadotrope function, some in
vivo studies demonstrated an inhibitory effect of
BDZ on LH release (120, 121), while other Authors
showed a positive effect of BDZ on LH secretion
(59, 108). Moreover, some studies in humans sho-
wed that AL increases LH pulse amplitude in nor-
mal women in early follicular phase and restores LH
pulsatility in women with hypothalamic stress-relat-
ed amenorrhea (122). As the stress-induced CRH
rise seems involved in the pathogenesis of hy-
pothalamic amenorrhea, it has been suggested that
AL would prevent the inhibition of LH release in hy-
pothalamic amenorrhea through reduction of the
stress-induced hyperactivation of the HPA axis
(122); this would point out the importance of some
BDZ, such as AL, in stress-related pathophysiolog-
ical conditions.
Taken all together, the data above mentioned in-
dicate a complex and differentiated modulatory in-
fluence of BDZ on the activity of hypothalamic-pi-
tuitary-gonadal axis, which, in turn, modulates in
different ways and at different levels the activity of
BDZ themselves (Table 1).
Lactotrope function
The influence of BDZ on PRL secretion is still con-
troversial: stimulatory, inhibitory or lacking influ-
ences have, in fact, been reported.
Very high diazepam doses have been found to
stimulate PRL release in schizophrenic patients but
other BDZ showed slight or no effect on either
basal or stimulated PRL release (116, 125, 126). On
the contrary, a stimulatory action of both acute and
chronic AL administration on basal PRL levels has
been shown in normal subjects as well as in patients
with panic disorder, respectively (62,126).
Evidence for BDZ inhibitory effect on both basal
and stimulated PRL secretion has been reported in
both animals (127-129) and humans (130).
The mechanisms by which BDZ modulate PRL se-
cretion are likely to involve GABAergic mediation.
A dual effect of GABA on PRL release has been
demonstrated: one stimulatory, likely to occur at
hypothalamic level, and one inhibitory, which seems
to be mediated at pituitary level. In agreement with
the central positive action of GABA on PRL release
is the evidence that the injection of GABA-A ago-
nists in the hypothalamus induces a clear rise in PRL
levels in rats (131). This effect seems mediated by
the inhibition of the tubero-infundibular dopamin-
ergic system; important GABA-dopamine interac-
tions in CNS, namely in the hypothalamus, are pre-
While there is clear evidence for the involvement of
PBR in the synthesis of gonadal steroids, few data
are so far available on the effects of these receptors
741

E. Arvat, R. Giordano, S. Grottoli, et al.
sent and inhibitory action of GABA and BDZ on do-
paminergic neurotransmission has been demon-
strated (132, 133).
(GABA/BDZ and PBR) led to hypothesize the exis-
tence of natural ligands with a physiological role.
The isolation of the family of endozepines, natural
ligand of both GABA/BDZ and PBR, allowed to
demonstrate the existence of a new system deeply
involved in many central, neuroendocrine and pe-
ripheral actions specifically mediated by GABA/BDZ
or PBR activation. As classical BDZ mainly bind GA-
BA/BDZ binding sites, their effects are likely to re-
flect the GABA/BDZ-mediated actions of endo-
zepines. However, unlike classical BDZ, endoze-
pines strongly control the processes of steroido-
genesis in all steroidogenetic tissues through PBR
activation. In CNS, PBR activation stimulates the
synthesis of the neurosteroids, which, in turn, mod-
ulate GABAergic neurotransmission by acting on
GABA/BDZ receptors. So, a tight interplay between
GABA, BDZ and neurosteroids became apparent
in the brain. Among the neuroendocrine activities
of BDZ, the inhibitory effect on the HPA function
seems to be the most important. Noteworthy,
among the various BDZ, AL showed the most
marked inhibitory effect on both spontaneous and
stimulated HPA activity, in agreement with its pe-
culiar efficacy in panic disorders and depression,
where the HPA hyperactivation seems to be in-
volved in pathophysiology of the disease. For these
reasons, BDZ, especially AL, may be a good tool to
study HPA neuroregulation. Moreover, the effects
of these substances have to be taken into account
when endocrinological investigations are per-
formed as well as before treating patients with sus-
pected adrenal impairment.
It had been hypothesized that PBR could mediate
the inhibitory effect of BDZ on PRL secretion at pi-
tuitary level. Actually, PBR ligands display pituitary
BDZ binding with more affinity than central BDZ/GA-
BA agonists (1). However, more recent data showed
that PBR ligands have no effect on PRL release from
pituitary gland, while central BDZ/GABA agonists
inhibit both basal and stimulated PRL secretion in
vitro, thus indicating that the GABA/BDZ receptor
complex mediates the pituitaric effects of BDZ on
PRL release (127).
Finally, direct positive influence of GABA on PRL
release has also been shown, indicating a complex
influence of GABA/BDZ on PRL secretion mediated
at different levels (134).
From a clinical point of view, the effect, if any, of
chronic BDZ treatments on PRL levels and/or the ef-
fects of BDZ in conditions of hyperprolactinemia are
scanty and do not indicate a strong influence of
these substances on the mechanisms deeply con-
trolling PRL (130, 135, 136); thus, further studies are
needed to clarify the real physiological and clinical
impact of BDZ in the control of lactotrope function
(Table 1).
Thyrotrope function
The influence of BDZ on thyrotrope function does not
appear remarkable but data available so far are scanty.
BDZ have been reported to inhibit TSH respon-
siveness to pharmacological stimulations in animals
(130). Moreover, BDZ have been reported to be
able to blunt the TSH response to TRH in rat pitu-
itaries through a competition for the TRH receptor
(109). On the contrary, other in vitro studies did not
confirm the inhibitory effect of BDZ on either basal
or TRH-stimulated TSH release (32, 127).
Studies in humans showed that neither acute nor
protracted BDZ administration modified basal or
TRH-stimulated TSH secretion in normal subjects
or in patients with anxiogenic disorders, respec-
tively (102, 130, 137). Nevertheless, it is of interest
that thyroid hormones seem to influence the bind-
ing and function of the brain GABA/BDZ receptor
complex, suggesting an interplay between the hy-
pothalamo-pituitary-thyroid axis and GABA/BDZ
activity in the CNS (138), (Table 1).
ACKNOWLEDGMENTS
The Authors wish to thank Prof. Franco Camanni, Dr. Barbara
Maccagno, Josefina Ramunni, Lidia Di Vito, Laura Gianotti,
Fabio Lanfranco, Micaela Pellegrino for their participating in
the studies mentioned in this paper and Dr. Angela Bertagna,
Mrs. Anna Barbero and Marina Taliano for their skillful tech-
nical assistance.
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