Full text of DOI:10.1385/BTER:77:2:97

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Tissue and Blood Levels
of Zinc, Copper, and Magnesium
in Nitric Oxide Synthase
Blockade-Induced Hypertension
,1
2
1
˙
ÜMIT KEMAL S¸ENTÜRK,* IRFAN KAPUTLU, FILIZ GÜNDÜZ,
1
OKTAY KURU, AND OSMAN GÖKALP2
1Department of Physiology and 2Department of Pharmacology,
Akdeniz University Faculty of Medicine, Antalya, Turkey
Received March 7, 2000; Revised May 2, 2000;
Accepted May 21, 2000
ABSTRACT
The aim of this study was to determine the levels of tissue and
blood zinc (Zn), copper (Cu), magnesium (Mg) in nitric oxide (NO)
synthase blockade-induced hypertension. A group of albino rats
received a NO synthase inhibitor, NG-nitro-L-arginine-methyl ester
(L-NAME, 60 mg/kg/d) in their drinking water for 21 d. L-NAME
intake caused a progressive rise in this group’s resting mean arterial
blood pressure compared to a control group (p < 0.01). There were no
differences between the groups with regard to tissue and blood lev-
els of Zn or Cu; however, Mg concentrations were significantly lower
in the hypertensive rats’ erythrocytes (20.2% reduction from control
levels), cerebral cortex (17.0%), heart (9.1%), renal cortex (12%), renal
medulla (16.7%), and in the tissues of the caval vein (23.7%), mesen-
teric artery (29.8%), renal artery (18.4%), and renal vein (22.1%). There
were no significant Mg concentration changes in the hypertensive
group’s plasma, cerebellum, liver, duodenum, or aortal tissue. These
findings suggest that Mg depletion may play a role in the blood pres-
sure rise that occurs in the model of chronic NO synthase inhibition-
induced hypertension.
Index Entries: Nitric oxide; nitric oxide synthase; hypertension;
zinc; copper; magnesium.
*Author to whom all correspondence and reprint requests should be addressed.
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INTRODUCTION
The production of nitric oxide (NO) by endothelial cells has been
demonstrated to be an important factor in the regulation of blood flow
and arterial pressure in mammals (1). NO exerts a basal tonic relaxing
action on systemic vasculature, and acute chronic inhibition of NO syn-
thase (NOS), the enzyme that produces NO from L-arginine, induces
blood pressure elevation in all species that have been examined to date.
Chronic treatment with orally active NOS inhibitors, such as NG-nitro-L-
arginine-methyl ester (L-NAME), has attracted significant interest as a
model of hypertension. Treatment of rats with L-NAME causes a time-
and dose-dependent increase in blood pressure (1–3).
Many investigators have tried to identify links between elements
and blood pressure (BP) in an attempt to understand the causes of, and
develop possible treatments for, hypertension. Altered tissue or blood
levels of zinc (Zn), copper (Cu), and magnesium (Mg) have been
reported in some experimental hypertension models and in humans with
essential hypertension. One study documented higher red blood cell Zn
concentration in essential hypertensive patients (4), and the same finding
has been noted in erythrocyte and cardiac tissues from spontaneously
hypertensive rats (SHR) (5). In the case of Cu, studies have yielded con-
flicting results, but some have reported elevated levels in hypertensive
human and hypertensive rat models (6–8). Magnesium, a potent inhibitor
of vascular smooth-muscle contraction, also plays a role in the regulation
of blood pressure as a vasodilator (9,10). Mg deficiency has been consid-
ered as a risk factor for hypertension (11) and low levels of Mg were
reported in essential hypertensive patients and in hypertensive animal
models (9).
Although relation of elements and hypertension were studied exten-
sively in different points of view in experimental models and hyper-
tensive patients, to our knowledge there is no information about the
possible alterations in Zn, Cu, Mg concentrations in NO-deficiency hy-
pertension model. We sought to investigate the levels of tissue and blood
Zn, Cu, and Mg in NOS blockade-induced hypertension in rats.
MATERIALS AND METHODS
Forty male albino rats (Akdeniz University Animal Care and Usage
Unit, Antalya, Turkey) weighing 250–290 g were used in two steps of this
experimental study. Twenty rats in the control group were given stan-
dard rat chow (manufactured by Korkutelim Co.) and tap water ad libi-
tum, and the 20 animals in the hypertensive group received 60 mg/kg/d
L-NAME (Sigma Chemical Company, St. Louis, MO) in their drinking
water for 21 d. Each gram of standard rat chow contained 10.5 µg of Zn,
1.52 µg of Cu, and 900 µg of Mg. To monitor the expected rise in blood
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pressure, all L-NAME-treated rats were subjected to weekly training for
blood pressure measurement by the tail-cuff method (May BPHR-200,
Commat Company, Turkey), as described in our previous study (12).
Step 1. At the end of 21 d, 24 animals (12 from each group) were
anesthetized with urethane (1 g/kg). In each animal, we drew
a blood sample from the abdominal aorta and then removed
tissues for study. We measured the concentrations of Zn, Cu,
and Mg in the plasma, cerebral cortex, cerebellum, heart, liver,
duodenum, and the kidney cortex and medulla.
Step 2. After the analysis was completed for Step 1, we decided
to run another phase of the study based on these results. The
remaining 16 animals (8 from each group) were anesthetized
in the manner described above, and we drew a blood sample
and removed the aorta, caval vein, mesenteric artery, renal
artery, and renal vein. These tissues and erythrocytes were
analyzed for Mg levels only.
For the analysis process, dry tissue samples were digested with
concentrated HNO3 at 65˚C until the mixture became clear. After the
digestion process, we used a Zeeman-effect atomic absorption spectro-
photometer (Hitachi Z-8000) equipped with a flame and furnace to mea-
sure the element concentrations in each tissue, plasma, or erythrocyte
sample.
We applied the Student’s t-test for statistical analysis, and all results
are expressed as mean SD; p values < 0.05 were accepted as significant.
RESULTS
During the feeding period, there were no differences between the
two groups with regard to daily water and food consumption or weight
gain. Figure 1 illustrates the effect that L-NAME treatment had on the
animals’ blood pressure. The mean arterial blood pressure increased
progressively in the L-NAME-treated rats, reaching 176.5 19.7 mm Hg
(n = 20) at the end of the treatment period, compared to 110.6 9.5 mm
Hg in the untreated controls (n = 20).
Step 1. Tables 1 and 2 list the plasma and tissue levels of Zn,
Cu, and Mg for the two groups. There were no significant dif-
ferences between hypertensive and control rats with regard to
plasma and tissue levels of Zn and Cu; however, some of the
hypertensive rats’ tissues contained significantly less Mg than
the same tissues in their untreated counterparts. The tissues
with statistically lower Mg levels were cerebral cortex (17.0%
reduced from control levels), heart (9.1% reduced), renal cor-
tex (12% reduced), and renal medulla (16.7% reduced).
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Fig. 1. Changes in mean arterial pressure induced by L-NAME. Values are
mean SD; n = 20 per group. **p < 0.01, control versus hypertensive group.
Table 1
Tissue (µmol/g Dry Weight) and Plasma (µmol/L) Zinc and Copper Levels
of Control and Hypertensive Groups
Note: Values are mean SD; n = 12 per group. *p < 0.05; **p < 0.01, control ver-
sus hypertensive group.
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Table 2
Tissue (µmol/g Dry Weight) and Plasma (µmol/L) Magnesium
Levels of Control and Hypertensive Groups
Note: Values are mean SD; n = 12 per group. *p < 0.05; **p < 0.01, con-
trol versus hypertensive group.
Table 3
Artery and Vein (µmol/g Dry Weight), Erythrocyte (µmol/g hb)
Magnesium Levels of Control and Hypertensive Groups
Note: Values are mean SD; n = 8 per group. *p < 0.05; **p < 0.01, con-
trol versus hypertensive group.
Step 2. Heart and kidney Mg levels were significantly lower in
the hypertensive group, and because these organs are known to
play important roles in blood pressure regulation, we focused
specifically on vascular Mg alterations in the second phase of
the experiment (Table 3). When the two groups were compared,
Mg levels were significantly lower in the hypertensive rats’ ery-
throcytes (20.2% reduced from control levels) and tissues of the
caval vein (23.7% reduced), mesenteric artery (29.8% reduced),
renal artery (18.4% reduced), and renal vein (22.1% reduced).
DISCUSSION
Currently, we know much more about the roles that elements play
in hypertension than about how hypertension affects the levels of these
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S¸entürk et al.
elements. The latter has generally been studied in animal hypertension
models. To our knowledge, ours is the first study to investigate the lev-
els of Zn, Cu, and Mg in NOS blockade-induced hypertension, a model
that has gained popularity in recent years because of its potential paral-
lels with human cardiovascular changes. The results of many studies
indicate that NO plays an important role in regulating arterial pressure
(1). Essential hypertension is a medical problem of growing importance,
and a recently proposed theory suggests that NO deficiency is one of the
mechanisms behind this condition (2,3).
We administered the NOS inhibitor L-NAME to rats orally via their
drinking water and induced a progressive rise in blood pressure over
3 wk of treatment. Our comparison of tissue and plasma concentrations
of the three elements showed that the hypertensive and normotensive
rats had similar blood and tissue concentrations of Zn and Cu, but that
the hypertensive animals had significantly lower levels of Mg in their
erythrocytes, cerebral cortex, heart, renal cortex and medulla, and in tis-
sues of the caval vein, mesenteric artery, renal artery, and renal vein.
Zinc is a cofactor in several enzymatic systems that are involved in
regulating blood pressure. These include the phosphodiesterase, phos-
pholipase C, carbonic anhydrase, and angiotensin-converting enzyme
systems, the latter being of particular importance (13). The Ca-ATPase
pump is also affected by zinc excess. Data from other studies in experi-
mental hypertension models have shown that hypertensive rats have ele-
vated Zn levels in their erythrocytes and tissues (5,8,14); however, this
was not the case in our experiment. As mentioned, we also found that
our hypertensive and control animals had similar Cu concentrations in
their blood and tissues. Although there is conflicting evidence as to how
Cu contributes to hypertension, it is generally accepted that SHR have
elevated Cu levels in their blood and tissues (7,14).
We noted some important differences when we compared the results
with our NOS blockade-induced hypertension model to previous find-
ings with other experimental hypertension models and to studies on
essential hypertension in humans. These other reports suggested that
blood pressure elevation causes the changes that were observed in blood
and tissue concentrations of Zn and Cu, but in our model, the levels of
Zn and Cu were similar in the hypertensive and control rats. Our study
did show that Mg levels are affected by elevated blood pressure, but the
fact that Zn and Cu were not affected raises suspicions about these other
authors’ conclusions. It may be that blood pressure elevation itself does
not alter Zn and Cu levels, but that agents used to induce hypertension
in these models or some metabolic alterations in hypertension state are
the responsible factors.
Concerning Mg levels, most clinical and experimental studies have
demonstrated that elevated blood pressure leads to a reduction in blood and
tissue concentrations of this element (9,15–19). In accord with these find-
ings, our work clearly demonstrates that hypertension reduces erythrocytes
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Minerals in NO-Induced Hypertension
103
and tissue concentrations of Mg in a NOS blockade-induced hypertension
model. The first phase of the study showed that, compared to the
untreated group, Mg levels were reduced in the hypertensive rats’ cerebral
cortex, heart, and renal cortex and medulla. When, based on these results,
we focused more specifically on Mg concentration changes in the vascular
system, we also found reduced levels in erythrocytes and in tissues from
the caval vein, mesenteric artery, renal artery, and renal vein.
Clinical studies on essential hypertension in humans have demon-
strated subnormal levels of Mg in serum, erythrocytes, and platelets (17)
and decreased free intracellular Mg in lymphocytes (18) and erythrocytes
(19). Although their results have not been confirmed by others, Kjeldsen
et al. (20) found increased Mg levels in the erythrocytes of patients with
essential hypertension, and Leblondel and Allain (14) found elevated lev-
els in the brain and heart tissue of SHR. However, similar to other stud-
ies, the latter authors did report reduced blood and serum Mg levels in
SHR. Hypomagnesemia is a common finding in SHR, and a series of
investigations have documented mildly reduced levels in cerebrum,
heart, lung, kidney, muscle, and bone tissues (9,15,16). Our results con-
cur with these findings in terms of the reported locations (brain, heart,
kidney) and degrees of reduction (9.1–17.0%) in Mg concentrations. We
found even more striking Mg reductions in the vessel tissue we studied,
but could not compare these results with other findings because no other
research to date has focused on the relationship between hypertension
and vessel tissue Mg levels.
Integrating our findings with those of other authors, we suggest that
several mechanisms may explain the Mg changes that occur in NOS
blockade-induced hypertension; however, these do not satisfactorily
account for the alterations that have been documented in SHR. First, we
can state with certainty that the reduced Mg concentrations observed in
our study did not result from dietary insufficiency, because the treated
and untreated rats consumed similar amounts of food. Typically, Mg
deficiency results from Mg loss from the gastrointestinal tract or the kid-
ney (21). It is possible that L-NAME might have a specific negative
impact on Mg absorption, but Mg deficiency resulting from any malab-
sorptive process in the hypertensive rats seems unlikely, as there was no
significant difference between the groups in terms of weight gain.
As mentioned, Mg loss can also occur through magnesuria. Reabsorp-
tion of Mg in the proximal tubule is affected by the load of filtered Na (21),
and some investigations have noted that animals treated with L-NAME
have an elevated level of filtered Na (3,22). Thus, L-NAME intake may
cause magnesuria. In addition, parathyroid hormone is known to stimulate
Mg transport in the thick ascending limb of the loop of Henle (23), and a
study in humans has shown that NO modulates parathyroid hormone
secretion (24). If a NOS blockage affects parathyroid hormone secretion,
this may result in magnesuria. Renal interstitial diseases and those that
affect the tubules or glomeruli have been associated with renal Mg wasting
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(21). Glomerulosclerosis, which can be caused by chronic NOS inhibition
(2,25), may also lead to renal Mg loss in L-NAME-treated animals.
Finally, Mg redistribution can take place through the action of cer-
tain hormones, with no resultant net loss of Mg. Studies have shown that
L-NAME treatment causes a rise in blood levels of corticosterone, adreno-
corticotropic hormone, thyroxine, and testosterone (26,27). In addition to
these hormones, Erlich and Rosendhal (28) suggested that chronic NOS
inhibition may lead to hyperinsulinemia, and insulin appears to be one
of the most important factors in the regulation of plasma and intracellu-
lar Mg concentrations (21).
Although research has not definitively explained the reasons behind
the Mg changes that occur in NOS blockade-induced hypertension, a
number of studies have suggested that a Mg deficit should be considered
a cardiovascular risk factor (29). Mg may play an important role in the
modulation of peripheral resistance. Both in vitro and in vivo experiments
have shown that Mg deficiency increases vascular tone (14). Altura et al.
(30) showed that, compared to normal rats, Mg-deficient rats have re-
duced arteriolar, venular, and precapillary lumen sizes, and fewer micro-
vessels overall. These effects might be the result of the elevated tissue Ca
levels that arise secondary to Mg deficiency. This enhanced Ca influx is
thought to occur via the Na/Ca-exchange mechanism (31). Furthermore,
some studies claim that the increased Ca influx into endothelial cells that
occurs as a consequence of decreased Mg levels increases the basal level of
NO release (32–34). Although there is still controversy over the effect
of Mg alteration on NO, Laurant and Berthelot have suggested that NO
may be involved in Mg-induced vascular relaxation (35). The findings in
endothelium are unclear, but it is certain that reduced Mg concentration
in smooth-muscle cells boosts Ca influx into these cells and increases vas-
cular tone (10,32,33). This effect could explain the connection between
hypertension and Mg deficiency and why this deficiency accelerates the
development of hypertension in SHR (36).
The vessel tissue of the hypertensive group in our study exhibited
markedly reduced Mg levels. This finding may indicate that a drop in
Mg accelerates, or acts in, the induction of hypertension by chronic NOS
inhibition because of L-NAME. The positive effect of dietary Mg content
on blood pressure in humans and animals is already known (36). Mg
supplementation has also been shown to significantly lower blood pres-
sure levels in deoxycorticosterone (DOCA)–salt hypertensive rats and
SHR (10,37). In the light of this, it is reasonable to suggest that Mg sup-
plementation might also have a beneficial effect on blood pressure levels
in NOS blockade-induced hypertension.
In summary, we found that in a NOS blockade-induced hyper-
tension model, hypertension does not significantly alter blood and tis-
sue Zn and Cu concentrations. Interestingly, however, we report the
first finding of a significant deficit in erythrocyte and tissue Mg levels
in this rat model of hypertension. These data suggest that tissue Mg
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Minerals in NO-Induced Hypertension
105
may contribute to the hypertension that develops under conditions of
chronic NOS inhibition.
ACKNOWLEDGMENT
This work was supported by the Scientific and Technical Research
˙
Council of Turkey (TUBITAK) grant 198S101, SBAG-AYD-220.
REFERENCES
1. J. Navarro, A. Sanchez, J. Saiz, L. M. Ruilope, J. Garcia-Estan, C. Romero, et al., Hor-
monal, renal, and metabolic alterations during hypertension induced by chronic inhi-
bition of NO in rats, Am. J. Physiol. 267, R1516–R1521 (1994).
2. M. O. Riberio, E. Antunes, G. Nucci, S. M. Lovisolo, and R. Zatz, Chronic inhibition
of nitric oxide synthesis, a new model of arterial hypertension, Hypertension 20,
298–303 (1992).
3. Jr R. D. Manning, L. Hu, and J. F. Reckelhoff, Role of nitric oxide in arterial pressure
and renal adaptations to long-term changes in sodium intake, Am. J. Physiol. 272,
R1162–R1169 (1997).
4. G. Frithz and G. Ronquist, Increased red cell content of Zn2+ in essential hyperten-
sion, Acta Med. Scand. 205, 647–649 (1979).
5. J. G. Henrotte, M. Santarromana, G. Franck, and R. Bourdon, Blood and tissue zinc
levels in spontaneously hypertensive rats, J. Am. Coll. Nutr. 9, 340–343 (1990).
6. G. Vivoli, P. Borella, P. Bergomi, and G. Fantuzzi, Zinc and copper levels in serum,
urine, and hair of humans in relation to blood pressure, Sci. Total Environ. 66, 55–64
(1987).
7. A. Berthelot, C. Luthringer, and A. Exinger, Trace elements during the development
of hypertension in the spontaneously hypertensive rat, Clin. Sci. 72, 515–518 (1987).
8. M. S. Clegg, F. Ferrel, and C. L. Keen, Hypertension-induced alterations in copper
and zinc metabolism in Dahl rats, Hypertension 9, 624–628 (1987).
9. S. Wallach and R. L. Verch, Tissue magnesium in spontaneously hypertensive rats,
Magnesium 5, 33–38 (1986).
10. P. Laurant, J. P. Kantelip, and A. Berthelot, Dietary magnesium supplementation
modifies blood pressure and cardiovascular function in mineralocorticoid–salt hyper-
tensive rats but not in normotensive rats, J. Nutr. 125, 830–841 (1995).
11. H. Karppanen, Epidemiologic evidence for considering magnesium deficiency as a
risk factor for cardiovascular diseases, Magnesium Bull. 12, 80–86 (1990).
12. I. Kaputlu, G. Sadan, B. Karayalcin, and A. Boz, Beneficial effects of pentoxifylline on
cyclosporine-induced nephrotoxicity, Clin. Exp. Pharmacol. Physiol. 24, 365–369 (1997).
13. B. L. Vallee and K. H. Falchuk, The biochemical basis of zinc physiology, Physiol. Rev.
73, 79–118 (1993).
14. G. Leblondel and P. Allain, Altered element concentrations in tissues of sponta-
neously hypertensive rats, Biomed. Pharmocother. 42, 121–129 (1988).
15. N. Saito, G. C. Abbu, Y. Konishi, S. Nishiyama, and T. Okada, Magnesium, calcium
and trace elements in spontaneously hypertensive rats, Clin. Exp. Pharmacol. Physiol.
22(Suppl. 1), S212–S214 (1995).
16. J. G. Henrotte, G. Franck, M. Santarromana, and R. Bourdon, Tissue and blood mag-
nesium levels in spontaneously hypertensive rats, at rest and stressful conditions,
Magnesium Res. 4, 91–96 (1991).
17. R. M. Touyz, F. J. Milne, and S. G. Reinach, Intracellular Mg2+, Ca2+, Na2+ and K+ in
platelets and erythrocytes of essential hypertension patients: relation to blood pres-
sure. Clin. Exp. Hypertens. 14, 1189–1209 (1992).
Biological Trace Element Research
Vol. 77, 2000

106
S¸entürk et al.
18. K. Kisters, M. Tepel, C. Spieker, K. H. Dietl, M. Barenbrock, K. H. Rahn, et al.,
Decreased cellular Mg2+ concentrations in a subgroup of hypertensives-cell models
for the pathogenesis of primary hypertension. J. Hum. Hypertens. 11, 367–372 (1997).
19. L. M. Resnick, R. K. Gupta, and J. H. Laragh, Intracellular free magnesium in ery-
throcytes of essential hypertension: relation to blood pressure and serum divalent
cations. Proc. Natl. Acad. Sci. USA 81, 6511–6515 (1984).
20. S. E. Kjeldsen, O. M. Sejersted, P. Frederichsen, P. Leren, and I. K. Eide, Increased ery-
throcyte magnesium content in essential hypertension, Scand. J. Clin. Lab. Invest. 50,
395–400 (1990).
21. R. K. Rude, Magnesium metabolism and deficiency, Endocrinol. Metab. Clin. North Am.
22, 377–395 (1993).
22. T. Nakamura, A. M. Alberola, F. J. Salazar, Y. Saito, T. Kurashina, J. P. Granger, et al.,
Effects of renal perfusion pressure on renal interstitial hydrostatic pressure and Na+
excretion: role of endothelium-derived nitric oxide, Nephron 78, 104–111 (1998).
23. C. de Rouffignac, B. Mandon, M. Wittner, and A. di Stefano, Hormonal control of
renal magnesium handling, Miner. Electrolyte Metab. 19, 226–231 (1993).
24. F. E. Kaiser, M. Dorighi, J. Muchnick, J. E. Morley, and P. Patrick, Regulation of
gonadotropins and parathyroid hormone by nitric oxide, Life Sci. 59, 987–992 (1996).
25. A. Zanchi, N. C. Schaad, M. C. Osterheld, E. Grouzmann, J. Nussberger, H. R. Brun-
ner, et al., Effect of chronic NO synthase inhibition in rats on renin–angiotensin sys-
tem and sympathetic nervous system, Am. J. Physiol. 268, H2267–H2273 (1995).
26. M. Giordino, M. Vermeulen, A. S. Trevani, G. Dran, G. Andonegui, and J. R. Geffner,
Nitric oxide synthase inhibitors enhance plasma levels of corticosterone and ACTH,
Acta Physiol. Scand. 157, 259–264 (1996).
27. M. Haluzik, J. Nedvidkova, V. Kopsky, J. Jahodova, B. Horejsi, and V. Schreiber,
The changes of the thyroid function and serum testosterone levels after long-term
L-NAME treatment in male rats, J. Endocrinol. Invest. 21, 234–238 (1998).
28. Y. Erlich and T. Rosenthal, Chronic hypertension leads to hyperinsulinemia in
Sprague–Dawley rats treated with nitric oxide synthase inhibitor, Am. J. Hypertens. 11,
1129–1133 (1998).
29. R. M. Mclean, Magnesium and its therapeutic uses-a review, Am. J. Med. 96, 63–76
(1994).
30. B.M. Altura, B.T. Altura, A. Gebrewold, H. Ising, and T. Ghünter, Magnesium defi-
ciency and hypertension: correlation between magnesium-deficient diets and micro-
circulatory changes in situ, Science 223, 1315–1317 (1984).
31. A. Zhang, B. T. Altura, and B. M. Altura, Endothelial cells are required for inhibition
of contractile responses induced by reduction in extracellular magnesium and
sodium ions in rat aortic smooth muscle. Microcirc. Endothelium Lymphatics 6, 427–435
(1990).
32. C. Szabo, V. Berczi, F. Schneider, A. G. Kovach, and E. Monos, Role of endothelium
in the response of the vein wall to magnesium withdrawal, Pflugers Arch. 420,
140–145 (1992).
33. D. D. Ku and H. S. Ann, Differential effects of magnesium on basal and agonist-
induced EDRF relaxation in canine arteries, J. Cardiovasc. Pharmacol. 17, 999–1006
(1991).
34. I. T. Mak, A. M. Komarov, T. L. Wagner, R. E. Stafford, B. F. Dickens, and W. B.
Weglicki, Enhanced NO production during Mg deficiency and its role in mediating
red blood cell glutathione loss, Am. J. Physiol. 271, C385–C390 (1996).
35. P. Laurant and A. Berthelot, Influence of endothelium on Mg2+-induced relaxation in
noradrenaline-contracted aorta from DOCA–salt hypertensive rat, Eur. J. Pharmacol.
258, 167–172 (1994).
36. P. Laurant, S. Robin, and A. Berthelot, Magnesium deficiency increases vasoconstric-
tor activity without affecting blood pressure of aged spontaneously hypertensive rats,
Magnes. Res. 10, 107–117 (1997).
37. M. Adachi, Y. Nara, M. Mano, and Y. Yamori, Effect of dietary magnesium supple-
mentation on intralymphocytic free calcium and magnesium in stroke-prone sponta-
neously hypertensive rats, Clin. Exp. Hypertens. 16, 317–326 (1994).
Biological Trace Element Research
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