(Hypertension. 1996;27:184-189.)
© 1996 American Heart Association, Inc.
Articles |
From the Department of Medicine, St George Hospital, University of New South Wales, Sydney, NSW, Australia.
Correspondence to Prof J.A. Whitworth, Department of Medicine, St George Hospital, Kogarah, NSW 2217, Australia. E-mail jwhitworth@unsw.edu.au.
| Abstract |
|---|
|
|
|---|
Key Words: adrenocorticotropic hormone arginine blood pressure rats corticosterone hypertension, experimental
| Introduction |
|---|
|
|
|---|
ACTH injection raises BP in rats,8 9 10 and the rise depends on intact adrenal glands.9 Inhibition of NO synthesis with oral N-nitro-L-arginine raises BP in SD rats and has an additive effect on ACTH-induced hypertension.11 These results are compatible with the notion that the hypertension induced by ACTH is not a consequence of NO inhibition but could also be explained by partial inhibition of NO by both treatments. Glucocorticoids are known to inhibit the expression of an inducible NO synthase in vascular endothelial cells but are reported not to affect the constitutive enzyme.12 L-NAME, an NO synthase inhibitor, increased corticosterone secretion dose dependently in the rat, suggesting that adrenal steroidogenesis was negatively regulated by endogenous NO.13
In 1991, Chen and Sanders14 reported that exogenous L-Arg decreased BP to normotensive levels in Dahl salt-sensitive rats but did not modify BP in salt-resistant rats. In contrast, L-Arg did not alter the development of hypertension in spontaneously hypertensive rats.14 The present study examined the effects of D- and L-Arg on ACTH-induced increases in BP and serum corticosterone concentration in SD rats.
| Methods |
|---|
|
|
|---|
Experimental Protocols
Rats were randomly divided into six
groups (n=10 for each).
Group 1 (sham treatment) rats received 0.9% NaCl (0.25 mL/kg SC) twice
daily at 10 AM and 6 PM for 10 days (T1 through
T10). Group 2 (ACTH treatment) rats were injected subcutaneously twice
daily at 10 AM and 6 PM with synthetic
ACTH (0.5 mg/kg per day, 0.25 mL/kg) (Synacthen Depot,
CIBA-Geigy) for 10 days (T1 through T10). Group 3 (L-Arg+sham
treatment) rats were fed 50 g of food containing 0.6% L-Arg daily at
10:30 AM and received 0.9% NaCl by injection as for group
1. The food was made by mixing 24 g of L-Arg (free base) powder (Sigma
Chemical Co) with a commercial food powder (4000 g, Gordon's Specialty
Stock Feeds). Group 4 (L-Arg+ACTH treatment) rats were fed with L-Arg
as for group 3 and injected with ACTH as for group 2. Group 5
(D-Arg+sham treatment) rats were fed as for group 3 with D-Arg (free
base) (Sigma) instead of L-Arg. Group 6 (D-Arg+ACTH treatment) rats
were fed D-Arg as for group 5 and injected with ACTH as for group
2.
BP Measurement
SBP was recorded on alternate days by the
tail-cuff
method (Narco Biosystems, Inc) in conscious rats. At least four
consecutive cycles (inflation/deflation) were performed on each rat,
and the mean of the last three recordings, among which there
was not more than 10 mm Hg difference, was taken as the SBP. The
recordings taken over the 6 control days, were used as baseline
values.
Organ Weight Measurement
At death, adrenal, kidney, and heart
weights were measured and
expressed relative to body weight (grams organ weight per 100 g body
weight).
Biochemical Estimations
All urine, plasma, and serum samples
were stored at
-20°C until analysis. Plasma and urine samples were
centrifuged at 3000 rpm for 10 minutes and diluted 1:5 with
distilled water; sodium and potassium concentrations were measured by
flame photometry (model I.L 943 flame photometer, Coulter Pty
Ltd).
Serum Corticosterone Measurement
Serum samples were collected
in refrigerated plain Vacutainer
tubes 2.5 hours after ACTH injection and stored at -20°C after
centrifugation (3500 rpm for 15 minutes). Serum
corticosterone was measured by radioimmunoassay (DPC Coat-A-Count rat
corticosterone kit). The sensitivity of the assay is approximately 5.7
ng/mL, and the interassay and intra-assay variations were 4.8% and
4%, respectively, at mean values of 421 and 427 ng/mL.
Statistical Analysis
Results are expressed as mean±SEM
and were analyzed by
two-way repeated measures ANOVA for comparison of all groups
together and individual treatment groups with the appropriate control
group as well as for analysis of a single treatment group over
time. Pretreatment days were pooled to give a mean pooled control.
Student's t tests were performed to compare the group mean
of control days with each treatment day and the data between groups.
The probability value for Student's t test was modified by
the Hochberg method of multiple comparisons.
| Results |
|---|
|
|
|---|
|
Group 1: Sham Treatment
Sham treatment did not change SBP or
urinary Na+ or
K+ excretion but was associated with increased body weight,
urine volume, water intake, and food intake (Figs 1
and
2
). Food intake was 28±1 g (pooled
control) and ranged from 29±1 to 32±1 g during treatment. Serum
corticosterone concentration at death was 424±43 ng/mL (Fig
3
).
|
|
|
Group 2: ACTH Treatment
ACTH treatment increased SBP (from
127±2 to 165±6 mm Hg,
P<.001) and also reduced body weight and increased water
intake and urine volume (Figs 1
and 2
). Food
intake was 28±1 g (pooled
control) and ranged from 24±1 to 32±1 g during treatment.
Urinary
Na+ excretion increased on days T1, T5, and T7, with no
change in urinary K+ excretion (Fig 2
). Serum
corticosterone concentration at death was 1071±117 ng/mL (Fig
3
).
Group 3: L-Arg+Sham Treatment
SBP, urine volume, and
food intake did not change during L-Arg
treatment, whereas body weight increased and water intake decreased on
days T1 and T3 (Figs 1
and 4
). Food intake was
29±1 g
(pooled control) and ranged from 29±1 to 32±2 g during
treatment.
L-Arg ingested varied from 612±25 (T1) to 616±18 (T9) mg/kg per
day.
Urinary Na+ excretion decreased only on day T5, and urinary
K+ excretion consistently decreased (Fig 4
).
Serum
corticosterone concentration at death was 238±25 ng/mL (Fig
3
).
|
Group 4: L-Arg+ACTH Treatment
SBP was unchanged during
L-Arg+ACTH treatment, whereas body
weight decreased, and urine volume and water intake increased (Figs
1
and 4
). Food intake was 27±1 g (pooled
control) and ranged from 24±2
to 33±1 g during treatment. L-Arg ingested varied from 746±22
(T1) to
669±27 (T9) mg/kg per day. Urinary Na+ and
K+
excretions remained unchanged (Fig 4
). Serum corticosterone
concentration at death was 739±95 ng/mL (Fig 3
).
Group 5: D-Arg+Sham Treatment
SBP, urine volume, urinary
Na+ excretion, and
food intake did not change significantly during D-Arg treatment, but
body weight increased and water intake decreased on day T3 (Figs
1
and 5
). Food intake was 28±1 g (pooled
control) and ranged
from 25±0 to 29±1 g during treatment. D-Arg ingested varied from
554±74 (T1) to 582±18 (T9) mg/kg per day. Urinary
K+
excretion increased from day T5 on (Fig 5
). Serum
corticosterone
concentration at death was 393±23 ng/mL (Fig 3
).
|
Group 6: D-Arg+ACTH Treatment
SBP increased (from
124±1 to 152±5 mm Hg,
P<.001) during D-Arg+ACTH treatment; body weight decreased,
and urine volume and water intake increased (Figs 1
and
5
). Food intake
was 30±1 g (pooled control) and ranged from 25±0 to 34±2
g during
treatment. D-Arg ingested varied from 763±39 (T1) to 679±43 (T9)
mg/kg per day. Urinary Na+ excretion increased on days T5
and T7, as did urinary K+ excretion on days T3 through T9
(Fig 5
). Serum corticosterone concentration at death was
695±72 ng/mL
(Fig 3
).
Intergroup Comparisons
Group 1 (Sham Treatment) With
Group 2 (ACTH
Treatment)
SBP was consistently higher during ACTH than sham
injection (Figs 1
and 2
). In rats receiving
ACTH, water intake, urine
volume, and plasma Na+ concentration were higher and body
weight and plasma K+ concentration lower. ACTH produced
marked increases in adrenal, kidney, and heart weights and serum
corticosterone concentration compared with sham injection.
Group 1 (Sham Treatment) With Group 3 (L-Arg+Sham
Treatment)
No differences were observed in SBP or metabolic
effects between groups 1 and 3. Plasma and urinary K+ and
serum corticosterone concentrations were lower, and heart weight was
higher in L-Argtreated rats.
Group 1 (Sham
Treatment) With Group 5 (D-Arg+Sham
Treatment)
No significant differences were observed in SBP, urine
volume,
body weight, kidney weight, urinary Na+ and K+
excretions, or serum corticosterone concentration between groups 1 and
5. Compared with sham-treated rats, D-Argtreated rats showed
decreased water and food intakes and lower plasma Na+ and
K+ concentrations and adrenal weights.
Group 2 (ACTH Treatment) With Group 4 (L-Arg+ACTH
Treatment)
SBP was lower in rats treated with L-Arg+ACTH compared
with rats
treated with ACTH alone (Fig 1
). Urine volume, food intake,
adrenal
weight, urinary Na+ excretion, and plasma K+
concentration did not differ significantly. Water intake was lower
during L-Arg on days T5 and T7. The L-Arg+ACTHtreated group
lost less weight, and urinary K+ excretion was lower in
L-Argtreated rats on days T1, T5, and T7.
L-Arg+ACTHtreated rats had higher heart weights and lower plasma
Na+ concentrations, kidney weights, and serum
corticosterone concentrations.
Group 2 (ACTH Treatment)
With Group 6 (D-Arg+ACTH
Treatment)
SBP was similar in groups 2 and 6, except for day T6, when
it was
lower in D-Arg+ACTHtreated rats (Fig 1
). Body
weight, food intake,
adrenal weight, urinary Na+ excretion, and plasma
Na+ concentration did not differ. Urine volume was lower in
the D-Arg+ACTH group on days T5 and T7 and water intake was lower on
days T1 through T9, but urinary K+ excretion was
higher in D-Argtreated rats on days T5, T7, and T9.
D-Arg+ACTHtreated rats also had higher heart weights and lower
plasma K+ concentrations, kidney weights, and serum
corticosterone concentrations.
Group 3
(L-Arg+Sham Treatment) With Group 4
(L-Arg+ACTH Treatment)
SBP was increased in the L-Arg+ACTH
group compared with the
L-Arg+sham group on days T4 and T10 (Figs 1
and
4
). Urine volume
was higher in L-Arg+ACTHtreated rats, as was water intake,
but body weight was lower. Food intake was initially increased in
L-Arg+ACTHtreated rats on day T1 but subsequently became lower
than
that of L-Arg+sham rats. Similar amounts of L-Arg were ingested. In the
L-Arg+ACTH group, adrenal, kidney, and heart weights were higher, as
was serum corticosterone concentration, but plasma K+
concentration was lower. Urinary Na+ excretion was
increased in L-Arg+ACTHtreated rats on days T3, T5, and T9 as
well as urinary K+ excretion on days T3 and T5.
Group 5 (D-Arg+Sham Treatment) With Group 6
(D-Arg+ACTH
Treatment)
SBP was higher in the D-Arg+ACTH group (Figs
1
and 5
), as was
water intake and urine volume. Body weight was lower in
D-Arg+ACTHtreated rats, and although food intake was similar,
D-Arg+ACTHtreated rats ingested more drug than D-Arg+sham
rats.
D-Arg+ACTH treatment produced greater adrenal, kidney, and heart
weights and higher serum corticosterone and plasma Na+
concentrations. Plasma K+ was lower during ACTH.
Group 6 (D-Arg+ACTH Treatment) With Group 4
(L-Arg+ACTH
Treatment)
SBP was higher in D-Arg+ACTHtreated rats (Fig
1
). Drug intake,
metabolic effects, organ weights, urinary Na+
excretion, and serum corticosterone concentration did not differ
significantly between the two groups. Plasma Na+
concentration and urinary K+ excretion were higher in
D-Arg+ACTHtreated rats.
| Discussion |
|---|
|
|
|---|
L-Arg infusion induced short-lasting hypotension in both normotensive and essential hypertensive men and in normotensive rats.18 19 20 In humans, L-Arg infused into the left cubital vein over 30 minutes caused rapid-onset decreases in both SBP and diastolic pressure; with cessation of the infusion, BP returned to baseline after 20 minutes.18 However, in high doses both D- and L-Arg have vasodilator effects in the human forearm.21 In conscious unrestricted rats, a bolus of L-Arg produced a marked, dose-related but short-lasting hypotensive effect, which was blocked by pretreatment with atropine.19
We found that oral L-Arg attenuated the rise in BP produced by ACTH. It did not affect BP in control male SD rats, consistent with most previous reports.5 16 The decrease in urinary potassium excretion in the L-Arg+sham group may have been a consequence of a lower plasma potassium concentration, implying that potassium is moving into the cells or being sequestered in the gut, and was unrelated to urine output, food or water intakes, and serum corticosterone concentration. D-Arg did not modify ACTH hypertension (apart from day T6), indicating that the L-Arg effect is stereospecific. The amounts of D- and L-Arg given in our experiment were consistent with those in the previous study by Chen and Sanders,14 and the amounts of drug ingested were similar in all groups, indicating that the SBP and metabolic effects observed were not a consequence of fluctuating food intake.
In 1989, Palacios et al22 reported that incubation of adrenal cytosol with L-Arg stimulated guanylate cyclase activity accompanied by the formation of NO and citrulline, and this effect of L-Arg was inhibited by hemoglobin and NG-monomethyl-L-arginine, demonstrating that rat adrenals contain a constitutive NO synthase in both the cortex and medulla. The findings that L-Arg directly stimulated adrenal NO synthesis in vitro suggested that the L-ArgNO pathway may participate in the regulation of the secretion or action of glucocorticoids. In 1991, Adams et al13 reported that L-NAME increased corticosterone secretion dose dependently in the SD rat, suggesting that adrenal steroidogenesis was negatively regulated by endogenous NO.
In the present study, oral L-Arg but not D-Arg decreased serum corticosterone in sham-treated rats, consistent with the notion that L-Arg has effects on steroidogenesis attributable to NO.13 22 In contrast, both L- and D-Arg decreased serum corticosterone in ACTH-treated rats. This decrease could reflect increases in hepatic blood flow and hence corticosterone clearance, as at high doses both drugs are vasoactive.21 However, serum corticosterone concentrations in the L-Arg+ACTHtreated rats were still markedly increased compared with control rats and similar to those in D-Arg+ACTHtreated rats. Thus, the effect of L-Arg in preventing ACTH-induced hypertension is unlikely to reflect the blunting of ACTH-stimulated corticosterone secretion. However, the observations do raise the possibility that the role of L-Arg in other forms of hypertension, such as Dahl salt-sensitive hypertension, may in part reflect decreasing steroid production. In the Dahl/Rapp rat, oral L-Arg completely prevented salt-sensitive hypertension.13 This inhibition of salt-sensitive hypertension by L-Arg was prevented by dexamethasone,23 suggesting a role for dexamethasone-suppressible NO synthesis in the prevention of the hypertension. However, as L-Arg decreases steroid production, the role of dexamethasone might be permissive.
It has been assumed in a number of studies that oral L-Arg modulates BP by increasing vasodilator NO synthesis.14 23 24 Several reports indicated that there might be some impairment of NO synthesis in some varieties of hypertension.14 25 26 There are at least two types of NO synthase.7 One is constitutive and Ca2+/calmodulin dependent and releases NO for short periods in response to receptor or physiological stimulation.7 The other enzyme is inducible and Ca2+ independent and synthesizes NO for long periods.7 It is induced by endotoxin and some cytokines, and this induction is inhibited by glucocorticoids.7 12 27 Given that the effects of L-Arg in preventing and reducing ACTH hypertension in the rat do not appear to be a consequence of metabolic effects and are not simply explained by decreases in serum corticosterone concentrations, steroid-induced inhibition of NO activity leading to loss of vasodilatation is a likely candidate mechanism, but we did not examine this proposition in the present study.
In summary, oral L-Arg but not D-Arg decreased ACTH-induced increases in BP in SD rats. L-Arg decreased serum corticosterone concentrations in sham rats, and both L- and D-Arg reduced serum corticosterone in ACTH-treated rats. The effects of L-Arg on ACTH-induced hypertension cannot be attributed simply to changes in ACTH-stimulated corticosterone production.
| Selected Abbreviations and Acronyms |
|---|
|
| Acknowledgments |
|---|
Received June 27, 1995; first decision August 29, 1995; accepted October 24, 1995.
| References |
|---|
|
|
|---|
2. Palmer RM, Ferrige AG, Moncada S. Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor. Nature. 1987;327:524-526. [Medline] [Order article via Infotrieve]
3. Marletta MA. Nitric oxide: biosynthesis and biological significance. Trends Biochem Sci. 1989;14:488-492. [Medline] [Order article via Infotrieve]
4. Aisaka K, Gross SS, Griffith OW, Levi R. NG-methyl arginine, an inhibitor of endothelium-derived nitric oxide synthesis, is a potent pressor agent in the guinea pig: does nitric oxide regulate blood pressure in vivo? Biochem Biophys Res Commun. 1989;160:881-886. [Medline] [Order article via Infotrieve]
5.
Rees DD, Palmer RM, Moncada S. Role of
endothelium-derived nitric oxide in the regulation
of blood pressure. Proc Natl Acad Sci U S A. 1989;86:3375-3378.
6.
Gardiner SM, Compton AM, Bennett T, Palmer RM, Moncada
S. Control of regional blood flow by
endothelium-derived nitric oxide.
Hypertension. 1990;15:486-492.
7. Moncada S, Palmer RM, Higgs EA. Nitric oxide: physiology, pathophysiology and pharmacology. Pharmacol Rev. 1991;43:109-142. [Medline] [Order article via Infotrieve]
8.
Vazir H, Whitehouse BJ, Vinson GP, McCredie E.
Effects of prolonged ACTH treatment on adrenal steroidogenesis and
blood pressure in rats. Acta Endocrinol Copenh. 1981;97:533-542.
9. Whitworth JA, Hewitson TD, Ming L, Wilson RS, Scoggins BA, Wright RD, Kincaid-Smith P. Adrenocorticotrophin-induced hypertension in the rat: hemodynamic, metabolic and morphological characteristics. J Hypertens. 1990;8:27-36. [Medline] [Order article via Infotrieve]
10. Whitworth JA, Hewitson TD, Cornwallis C. Corticotrophin effects on blood pressure and fluid and electrolyte homeostasis in five strains of rats. Am J Hypertens. 1992;5:302-313. [Medline] [Order article via Infotrieve]
11. Li M, Dusting GJ, Whitworth JA. Inhibition of NO synthesis has an additive effect on hypertension induced by ACTH in conscious rats. Clin Exp Pharmacol Physiol. 1992;19:675-681. [Medline] [Order article via Infotrieve]
12.
Radomski MW, Palmer RM, Moncada S.
Glucocorticoids inhibit the expression of an inducible, but not the
constitutive, nitric oxide synthase in vascular
endothelial cells. Proc Natl Acad Sci
U S A. 1990;87:10043-10047.
13. Adams ML, Nock B, Truong R, Cicero TJ. Nitric oxide control of steroidogenesis: endocrine effects of NG-nitro-L-arginine and comparisons to alcohol. Life Sci. 1991;50:35-40.
14. Chen PY, Sanders PW. L-arginine abrogates salt-sensitive hypertension in Dahl/Rapp rats. J Clin Invest. 1991;88:1559-1567.
15. Baylis C, Mitruka B, Deng A. Chronic blockade of nitric oxide synthesis in the rat produces systemic hypertension and glomerular damage. J Clin Invest. 1992;90:278-281.
16. Baylis C, Harton P, Engels K. Endothelial derived relaxing factor controls renal hemodynamics in the normal rat kidney. J Am Soc Nephrol. 1990;1:875-881. [Abstract]
17.
Kirchner KA, Scanlon PH, Dzielak DJ, Hester RL.
Endothelium-derived relaxing factor responses in
DOCA-salt hypertensive rats. Am J Physiol. 1993;265:R568-R572.
18. Nakaki T, Hishikawa K, Suzuki H, Saruta T, Kato R. L-arginine-induced hypotension. Lancet. 1990;336:696. Letter. [Medline] [Order article via Infotrieve]
19. Cernadas MR, Riesco A, Gallego MJ, Grandes S, Lopez Farre A, Casado S, Hernando L, Caramelo C. L-arginine-induced hypotension. Lancet. 1990;336:1016-1017. [Medline] [Order article via Infotrieve]
20. Hishikawa K, Nakaki T, Suzuki H, Saruta T, Kato R. L-arginine-induced hypotension. Lancet. 1991;337:683-684. [Medline] [Order article via Infotrieve]
21. Calver A, Collier J, Vallance P. Dilator actions of arginine in human peripheral vasculature. Clin Sci. 1991;81:695-700. [Medline] [Order article via Infotrieve]
22. Palacios M, Knowles RG, Palmer RM, Moncada S. Nitric oxide from L-arginine stimulates the soluble guanylate cyclase in adrenal glands. Biochem Biophys Res Commun. 1989;165:802-809. [Medline] [Order article via Infotrieve]
23.
Chen PY, Sanders PW. Role of nitric oxide
synthesis in salt-sensitive hypertension in Dahl/Rapp rats.
Hypertension. 1993;22:812-818.
24.
Dananberg J, Sider RS, Grekin RJ. Sustained
hypertension induced by orally administered nitro-L-arginine.
Hypertension. 1993;21:359-363.
25.
Linder D, Kiowski W, Buhler FR, Luscher TF.
Indirect evidence for release of
endothelium-derived relaxing factor in human
forearm circulation in vivo. Circulation. 1990;81:1762-1767.
26. Panza JA, Quyyumi AA, Brush JE, Epstein SE. Abnormal endothelium-dependent vascular relaxation in patients with essential hypertension. N Engl J Med. 1990;323:22-27. [Abstract]
27. Esplugues JV, Martinez-Cuesta MA, Barrachina MD, Calatayud S, Whittle BJR. Involvement of endogenous nitric oxide in the inhibition by endotoxin and interleukin-1ß of gastric acid secretion. J Gastroenterol Hepatol. 1994;9:S45-S49.
This article has been cited by other articles:
![]() |
J. P.F. Chin-Dusting, B. A. Ahlers, D. M. Kaye, J. J. Kelly, and J. A. Whitworth L-Arginine Transport in Humans With Cortisol-Induced Hypertension Hypertension, June 1, 2003; 41(6): 1336 - 1340. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y.-k. Lou, C. Wen, M. Li, D. J. Adams, M.-x. Wang, F. Yang, B. J. Morris, and J. A. Whitworth Decreased Renal Expression of Nitric Oxide Synthase Isoforms in Adrenocorticotropin-Induced and Corticosterone-Induced Hypertension Hypertension, April 1, 2001; 37(4): 1164 - 1170. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. A. Whitworth, G. J. Mangos, and J. J. Kelly Cushing, Cortisol, and Cardiovascular Disease Hypertension, November 1, 2000; 36(5): 912 - 916. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Hypertension Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 1996 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |