Full text of DOI:10.1007/BF03345510

J. Endocrinol. Invest. 25: 769-772, 2002
Serum leptin levels are not influenced by arginine and
insulin infusion and by acute changes of GH
G. Radetti*, C. Tinelli**, C. Paganini*, M. Draghi***, D. Scarcella****, E. Bozzola***,
G. Aimaretti*****, G. Rondini***, and L. Tatò****
*Department of Pediatrics, Regional Hospital of Bolzano, Bolzano; **Biometric Unit-IRCCS San Matteo,
Pavia; ***Department of Pediatrics, University of Pavia, Pavia; ****Department of Pediatrics, University
of Verona, Verona; *****Division of Endocrinology and Metabolism, University of Turin, Turin, Italy
ABSTRACT. The aim of this study was to evalu-
ate the relationship between GH and leptin in a
group of short children and adolescents. Leptin
and GH serum levels were measured before and
during pharmacological stimulation tests (argi-
nine and insulin) in a group of 45 children (30
male, 15 female), mean age 8.6 3.9 yr, affected
by idiopathic isolated GH deficiency (GHD), and
in a group of 27 children (15 male, 12 female),
age 10.9 3.3 yr, with constitutional growth de-
lay. Results showed that basal and peak leptin
levels as well as the AUC were significantly high-
er in GHD patients compared to controls (p<0.05)
and correlated with BMI SDS (p<0.0001) in GHD
patients. No change in leptin serum levels was
observed during either stimulation test. No cor-
relation was found, however, between basal lep-
tin serum levels and basal, peak and the AUC of
GH during the tests. Moreover, no correlation
was found between the acute changes of serum
GH concentration during both stimulation tests
and leptin serum levels. The results suggest that
leptin and GH secretion is not correlated and
that leptin serum levels mainly reflect the
amount of fat tissue, which is higher in GHD pa-
tients.
(J. Endocrinol. Invest. 25: 769-772, 2002)
©2002, Editrice Kurtis
INTRODUCTION
ter of debate. Sudden changes of GH following argi-
nine infusion do not seem to alter leptin serum lev-
els (9), while acute GH treatment led to an increase
in leptin levels after 24 h in elderly (10) and young
patients affected by GH deficiency (GHD) (11), fol-
lowed by a significant decrease after 72 h (12).
Chronic GH treatment has been shown to reduce
leptin levels in GHD children (13) and to have no ef-
fect in elderly GHD patients (10).
The aim of our study was thus to verify, in a group of
45 children affected by GHD and in 27 controls, 1)
whether a basal leptin value could predict the re-
sponse of GH to a pharmacological stimulus (arginine
or insulin); 2) the relationship between GH and leptin
serum levels during the test; and 3) the effect of argi-
nine and insulin infusion on leptin serum values.
It is becoming clear that leptin should no longer be
considered as just a hormone modulating appetite
control and energy expenditure, but rather as an hy-
pothalamic neuromodulator controlling the secre-
tion of many pituitary hormones (1). Leptin has been
shown to play a major role in sexual development in
both animals (2) and humans (3, 4), and to influence
spontaneous GH secretion in rats (5) and IGF-I gene
expression in the liver, independently of GH (6).
It has been suggested that leptin could inhibit GH
secretion in humans, the latter being inversely cor-
related to body fat (7). Moreover, an inverse rela-
tionship between leptin and GH has been demon-
strated (8), although there is no direct evidence of
the role of leptin in inhibiting GH secretion. Whether
GH can influence serum leptin levels is still a mat-
MATERIAL AND METHODS
Subjects
Key-words: Leptin, GH, GH deficiency, arginine infusion, insulin-induced
hypoglycaemia.
Seventy-two children were investigated because of short
stature: 45 of them (30 boys, 15 girls) were considered to be
GHD, while the remaining 27 (15 boys, 12 girls) were only
growth retarded and served as controls. Their auxological da-
ta are shown in Table 1.
Correspondence: Dr. Giorgio Radetti, Dipartimento di Pediatria,
Ospedale Regionale, Via L. Boehler 5, 39100 Bolzano, Italia.
E-mail: giorgio.radetti@asbz.it
Accepted May 2, 2002.
769

AITT and GH changes do not influence leptin secretion
say coefficients of variation (CV) were less than 8.3 and 6.2%,
respectively.
Table 1 - Auxological parameters of GH-deficient patients and
controls.
GH levels were determined by using chemiluminescent enzyme
immunometric assay with a commercial kit (Immulite Growth
Hormone, DPC Diagnostic Products Corporation, Los Angeles,
CA, USA). The detection limit of the assay was 0.01 ng/ml; the in-
tra- and inter-assay CV were less than 6.5 and 6.2%, respectively.
To eliminate the inter-assay variation, all samples were mea-
sured in duplicate in the same assay.
Patients
45
Controls
27
Subjects
Male/Female
Age (yr)
30/15
15/12
8.6 3.9
75.6
10.9 3.3
59.3
% pre-pubertal
Height SDS
BMI SDS
-1.7 1.2
0.4 2.3
-0.8 1.4
-1.7 1.0
-0.4 1.2
-0.95 0.48
Statistical analysis
The results are expressed as mean and SD. Logarithmic trans-
formation was employed to normalize the distribution of leptin.
One-way analysis of variance (ANOVA) was used to determine
significant differences in leptin and GH concentrations between
patients and controls and a factorial model was used to adjust
for the covariate BMI SDS and age. The AUC during stimulation
tests was calculated according to the trapezoidal rule. Corre-
lations between variables was performed by Pearson r coeffi-
cient. A p value of less than 0.05 was considered to be statisti-
cally significant. All tests were two-sided. Analyses were per-
formed with Statistica for Windows software (StatSoft, Inc. 2000,
Tulsa, OK, U.S.A.)
Target height SDS
Height and Target height SDS according to Tanner (22); BMI SDS ac-
cording to Rolland-Cachera (23).
The diagnosis of GHD was based on the following criteria: height
<-2 SDS or <10th centile when corrected for parental target (ac-
cording to J.M. Tanner’s “Parents-allowed-for charts”) (14);
height velocity-SDS <25th centile for chronological age when
measured for more than 1 yr; bone age delay >2 yr compared
to chronological age; peak GH <10 μg/l in at least 2 consecutive
conventional pharmacological tests (15). No patient suffered
from any organic GHD, panhypopituitarism or multiple pituitary
hormone deficiency, all being affected by idiopathic isolated
GHD, as confirmed by a complete endocrine assessment and
pituitary MRI.
RESULTS
During both stimulation tests with insulin and argi-
nine (Tables 2 and 3), basal GH was similar in GHD
patients and controls, whereas peak GH and the
AUC were significantly lower in patients compared
to controls.
Basal and peak leptin levels were significantly high-
er in GHD patients compared to controls (Tables 2
and 3).
Study protocol
Serum leptin and GH levels were evaluated, after an overnight
fast between 08:00 h and 09:00 h at basal level and 30, 60 and
90 min following an arginine (0.5 g/bw iv) and an insulin (0.1
U/bw iv) infusion.
Leptin levels did not change significantly during
both stimulation tests despite a significant increase
in GH levels (Fig. 1).
Methods
Leptin levels were measured by RIA using a commercial kit
(Human Leptin RIA Kit, Linco Research Inc., St. Louis, MO, USA).
The sensitivity of the assay was 0.5 ng/ml; the intra- and inter-as-
Basal leptin significantly correlated with the BMI
Table 2 - GH and leptin secretory pattern in GH-deficient (GHD) patients and controls during the arginine stimulation test.
Basal GH
(ng/ml)
Peak GH
(ng/ml)
AUC GH
(ng/ml/30’)
Basal leptin
(ng/ml)
Peak leptin
(ng/ml)
AUC leptin
(ng/ml/30’)
GHD
Controls
p
0.86 0.91
0.94 0.66
NS
5.04 2.36
16.54 4.55
<0.001
15.77 7.90
47.95 18.42
<0.001
6.10 6.14
2.93 2.11
<0.05
6.13 6.10
3.56 3.24
<0.05
28.92 24.52
20.12 23.82
NS
Table 3 - GH and leptin secretory pattern in GH-deficent (GHD) patients and controls during the insulin stimulation test.
Basal GH
(ng/ml)
Peak GH
(ng/ml)
AUC GH
(ng/ml/30’)
Basal leptin
(ng/ml)
Peak leptin
(ng/ml)
AUC leptin
(ng/ml/30’)
GHD
Controls
p
0.81 0.81
0.86 0.89
NS
5.59 2.39
19.72 9.10
<0.001
18.14 9.92
62.48 24.43
<0.001
4.71 2.36
3.23 3.82
<0.05
5.58 2.48
3.82 4.12
<0.05
25.43 13.71
16.84 10.78
NS
770

G. Radetti, C. Tinelli, C. Paganini, et al.
20
15
10
5
GH
Leptin
age of body fat rather than a direct consequence
of GH excess (16).
We found a significant correlation between leptin
and BMI in GHD patients, suggesting that the in-
creased leptin levels merely represent the increased
fat mass of these subjects lacking the lipolitic ac-
tion of GH (17).
Leptin therefore appears to be an unlikely modu-
lator of GH secretion. In a recent paper (18), how-
ever, where leptin and GH secretion were analyzed
and time-cross-correlated over 24 h in a group of
short-normal pre-pubertal children, it was shown
that GH secretion leads leptin secretion in a positive
way by 5 and 2 h for boys and girls, respectively,
suggesting a positive direct leptin releasing effect
of GH on adipocytes. The same Authors indicate in
that paper that there is a significant correlation over
time with leptin leading GH at lag times 11 and 8.5
h for boys and girls, respectively. Thus, it seems
that leptin might still be a possible candidate for
modulation of GH secretion; this however could not
be demonstrated by our work, since the study pe-
riod was too short.
0
0
25
50
75
100
Time (min)
Fig. 1 - Mean (SD) of GH and leptin serum levels during arginine
and insulin stimulation tests in the 72 subjects.
SDS in GHD patients (r=0.70; p<0.0001) (Fig. 2),
but not in controls (r=0.35; p=NS). Furthermore, no
correlation was found between basal serum leptin
and basal values, peak and AUC of GH during both
tests.
DISCUSSION
Moreover, serum leptin was not influenced either
by arginine or insulin administration, confirming that
neither arginine (9) nor insulin (18) are able to stim-
ulate leptin secretion in the short term. A longer
period of exposure to insulin is probably needed
in order to evoke a response; this is supported by
clinical studies reporting a correlation between in-
sulin and leptin serum concentration (19), and by
in vitro studies of fat cell cultures showing that in-
sulin directly stimulates leptin secretion (20).
In conclusion, our findings obtained from a large
group of children, seem to suggest that leptin and
GH secretion are not correlated and that leptin
serum levels mainly reflect the amount of fat tissue,
which is increased in GHD patients.
The results of our study, in agreement with a pre-
vious report (9), fail to support the hypothesis of a
relationship between GH and leptin secretion, at
least over a short-term period. In fact, we could not
find either a correlation between basal leptin lev-
els and various parameters of GH secretion during
the stimulation tests, or between the profiles of GH
and leptin during the tests.
Acute GH administration has been previously
shown to affect leptin serum levels in absence of a
change in body composition (10-12); changes were
observed however only 24 h after GH administra-
tion.
Long-term studies failed to show a direct influence
of GH on leptin secretion. The decrease in leptin
levels observed after one year of GH treatment in a
group of GHD children was not apparent anymore
when expressed per unit fat mass (13); also in
acromegalic subjects the reduction in leptin ap-
pears to be more the result of a reduced percent-
ACKNOWLEDGMENT
We thank Dr. L. Gentili for his assistance in reviewing the English
version of the manuscript.
10
5
15
10
50
0
0
r=0.70; p<0.0001
r=0.35; NS
-5
-5
Fig. 2 - Correlation between BMI SDS
and basal leptin in GHD patients and
controls.
0
10
20
30
0
10
20
30
Basal leptin (ng/ml)
Basal leptin (ng/ml)
771

AITT and GH changes do not influence leptin secretion
REFERENCES
12. Lissett C.A., Clayton P.E., Shalet S.M. The acute leptin re-
sponse to GH. J. Clin. Endocrinol. Metab. 2001, 86: 4412-
4415.
1. Blum W.F. Leptin. The voice of the adipose tissue. Horm.
Res. 1997, 48: 2-8.
13. Matsuoka H., Fors H., Bosaeus I., Rosberg S., Albertsson-
Wikland K., Bjarnason R. Changes in body composition
and leptin levels during growth hormone (GH) treatment in
short children with various GH secretory capacities. Eur. J.
Endocrinol 1999, 140: 35-42.
2. Chehab F.F, Lim M.E., Lu R. Correction of the sterility de-
fect in homozygous obese female mice by treatment with
the human recombinant leptin. Nat. Gen. 1996, 12: 318-
320.
3. Montague C.T., Farooqi I.S., Whitehead J.P., et al. Con-
genital leptin deficiency is associated with severe early-
onset obesity in humans. Nature 1997, 387: 903-908.
14. Tanner J.M. Foetus into man: physical growth from con-
ception to maturity, 2nd ed. Castelmead Publications,
Ware, 1989.
4. Clement K., Vaisse C., Lahlou N., et al. A mutation in the
human leptin receptor gene causes obesity and pituitary
dysfunction. Nature 1998, 392: 398-401.
15. Cowell C.T. Short stature. In: Brook C.G.D. (Ed.), Clinical
paediatric endocrinology, 3rd ed. Blackwell Science,
Oxford, 1994, p. 136.
5. Carro E., Senaris R., Considine R., Casanueva F.F., Dieguez
C. Regulation of in vivo growth hormone secretion by lep-
tin. Endocrinology 1997, 138: 2203-2206.
16. Miyakawa M., Tsushima T., Murakami H., Isozaki O.,
Demura H., Tanaka T. Effect of growth hormone (GH) on
serum concentrations of leptin: study in patients with
acromegaly and GH deficiency. J. Clin. Endocrinol. Metab.
1998, 83: 3476-3479.
6. Thomas M.J., Pitts S.H., Siwitz W. Leptin stimulates hepatic
insulin-like growth factor (IGF)-I gene expression in vivo. In:
Endocrine Society, 79th Annual Meeting of the Endocrine
Society, Minneapolis, Minnesota, 1997, OR 40-42, p. 123.
17. Wabitsch M., Hauner H., Heinze E., Teller W.M. The role of
growth hormone/insulin-like growth factors in adipocyte
differentiation. Metabolism 1995, 44: 45-49.
7. Veldhuis J.D., Iranmanesh A., Ho K.K.Y., Waters M.J.,
Johnson M.L., Lizzaralde G. Dual defects in pulsatile GH
secretion and clearance subserve the hyposomatotropism
of obesity in man. J. Clin. Endocrinol. Metab. 1991, 72:
51-59.
18. Ghizzoni L., Mastorakos G., Street M.E., et al. Leptin, cor-
tisol, and GH secretion interactions in short normal pre-
pubertal children. J. Clin. Endocrinol. Metab. 2001, 86:
3729-3734.
8. Gill M.S., Toogood A.A., O’Neill P.A., et al. Relationship
between growth hormone status, serum leptin and body
composition in healthy and GH-deficient elderly subjects.
Clin. Endocrinol. (Oxf.) 1997, 47: 161-167.
19. Dagogo-Jack S., Fanelli C., Paramore D., Brothers J., Landt
M. Plasma leptin and insulin relationships in obese and
nonobese humans. Diabetes 1996, 45: 695-698.
20. Considine R.V., Sinha M.K., Heiman M.L., et al. Serum im-
munoreactive-leptin concentrations in normal-weight and
obese humans. N. Engl. J. Med. 1996, 334: 292-295.
9. Bennek C., Gehrt I., Keller A., et al. Arginine infusion
and/or acute changes of growth hormone levels do not
acutely alter leptin serum levels. J. Pediatr. Endocrinol.
Metab. 1999, 12: 847-851.
21. Wabitsch M., Jensen P.B., Blum W.F., et al. Insulin and cor-
tisol promote leptin production in cultured human fat cells.
Diabetes 1996, 45: 1435-1438.
10. Gill M.S., Toogood A.A., Jones J., Clayton P.E., Shalet S.M.
Serum leptin response to the acute and chronic adminis-
tration of growth hormone (GH) to elderly subjects with
GH deficiency. J. Clin. Endocrinol. Metab. 1999, 84: 1288-
1295.
22. Tanner J.M., Whitehouse R.H., Takaishi M. Standards from
birth to maturity for height, weight, height velocity and
weight velocity: British children. Arch. Dis. Child. 1966, 41:
613-635.
11. Nørrelund H., Gravholt C.H., Englaro P., et al. Increased
levels but preserved diurnal variation of serum leptin in
GH-deficient patients: lack of impact of different modes
of GH administration. Eur. J. Endocrinol. 1998, 138: 644-
652.
23. Rolland-Cachera M.F., Cole T.J., Sempé M., Tichet J.,
Rossignol C., Charraud A. Body mass index variations: cen-
tile from birth to 87 years. Eur. J. Clin. Nutr. 1991, 45: 13-
21.
772