Acute and chronic dose-response relationships for angiotensin, aldosterone, and arterial pressure at varying levels of sodium intake.
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We examined the acute and chronic dose-response relationships between intravenously infused angiotensin II (A II) and the resulting changes in arterial pressure and plasma aldosterone concentration at varying levels of sodium intake. Sequential analysis of plasma aldosterone at each A II infusion rate resulted in an acute dose-related increase in plasma aldosterone which was markedly attenuated after the first 24 hours of infusion, the final level being directly related to the dose of A II and inversely related to sodium intake. A II infused at 5,15, and 23 ng/kg per min was associated with an initial increase (2nd to 8th hour) in plasma aldosterone to 2,6, and 9 times control values, respectively, in dogs receiving 40 mEq Na+/day. But, after the 1st day, aldosterone averaged only 1, 1.7, and 3 times control values for the next 2 weeks at the same rates of A II infusion. Dogs receiving 120 mEq Na+/day during A II infusion exhibited only a transient increase in plasma aldosterone during the 1st day. Sustained hypertension developed over a period of a week at all doses of A II at normal and high sodium intake, but did not occur at any dose of A II in sodium-depleted dogs. Increasing sodium intake from 40 to 120 mEq/day resulted in higher levels of hypertension, 125% compared to 140% of ocntrol values for dogs infused with A II, 5.0 ng/kg per min. We conclude that primary angiotensin-induced hypertension need not be associated with increased levels of plasma aldosterone, which appears to remain elevated only with amounts of A II greater than those required to sustain a significant degree of hypertension. (+info)
Low calorie diet enhances renal, hemodynamic, and humoral effects of exogenous atrial natriuretic peptide in obese hypertensives.
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The expression of the natriuretic peptide clearance receptor is abundant in human and rat adipose tissue, where it is specifically inhibited by fasting. In obese hypertensives, plasma atrial natriuretic peptide (ANP) levels were found to be lower than in obese normotensives. Therefore, the increased adipose mass might influence ANP levels and/or its biological activity. The aim of the present study was to evaluate whether the humoral, hemodynamic, and renal effects of exogenous ANP in obese hypertensives might be enhanced by a very low calorie diet. Eight obese hypertensives received a bolus injection of ANP (0.6 mg/kg) after 2 weeks of a normal calorie/normal sodium diet, and blood pressure (BP), heart rate, ANP, cGMP, plasma renin activity, and aldosterone were evaluated for 2 hours before and after the injection. Diuresis and natriuresis were measured every 30 minutes. The patients then started a low calorie/normal sodium diet (510 kcal/150 mmol/d) for 4 days, and then the ANP injection protocol was repeated. The low calorie diet induced a slight weight loss (from 90.6+/-1.1 to 87. 7+/-1.2 kg; P<0.01), which was accompanied by increase of cGMP excretion (from 146.0+/-10.1 to 154.5+/-9.5 nmol/24 h; P<0.05) together with a reduction of BP (P<0.01 versus basal levels). ANP injection after diet was followed by an increase of ANP levels similar to that observed before diet, but plasma cGMP, diuresis, and natriuresis increased significantly only after diet. Similarly, the decrease of BP after ANP administration was significantly higher after diet (change in mean arterial pressure, -6.4+/-0.7 versus -4. 0+/-0.6 mm Hg; P<0.05) as well as that of aldosterone (P<0.01). These data show that a low calorie diet enhances the humoral, renal, and hemodynamic effects of ANP in obese hypertensives and confirm the importance of caloric intake in modulating the biological activity of ANP, suggesting that the natriuretic peptide system can play a role in the acute changes of natriuresis and diuresis associated with caloric restriction. (+info)
Aldosterone excretion rate and blood pressure in essential hypertension are related to polymorphic differences in the aldosterone synthase gene CYP11B2.
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Significant correlation of body sodium and potassium with blood pressure (BP) may suggest a role for aldosterone in essential hypertension. In patients with this disease, the ratio of plasma renin to plasma aldosterone may be lower than in control subjects and plasma aldosterone levels may be more sensitive to angiotensin II (Ang II) infusion. Because essential hypertension is partly genetic, it is possible that altered control of aldosterone synthase gene expression or translation may be responsible. We compared the frequency of 2 linked polymorphisms, one in the steroidogenic factor-1 (SF-1) binding site and the other an intronic conversion (IC), in groups of hypertensive and normotensive subjects. In a larger population, the relationship of aldosterone excretion rate to these polymorphisms was also evaluated. In 138 hypertensive subjects, there was a highly significant excess of TT homozygosity (SF-1) over CC homozygosity compared with a group of individually matched normotensive control subjects. The T allele was significantly more frequent than the C allele in the hypertensive group compared with the control group. Similarly, there was a highly significant relative excess of the conversion allele over the "wild-type" allele and of conversion homozygosity over wild-type homozygosity in the hypertensive group compared with the control group. In 486 subjects sampled from the North Glasgow Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) population, SF-1 and IC genotypes were compared with tetrahydroaldosterone excretion rate. Subjects with the SF-1 genotypes TT or TC had significantly higher excretion rates than those with the CC genotype. The T allele was associated with higher excretion rates than the C allele. However, no significant differences were found in excretion rate between subjects of different IC genotype. Urinary aldosterone excretion rate may be a useful intermediate phenotype linking these genotypes to raised BP. However, no causal relationship has yet been established, and it is possible that the polymorphisms may be in linkage with other causative mutations. (+info)
Sodium requirement of adult cats for maintenance based on plasma aldosterone concentration.
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The sodium requirement of adult cats for maintenance was determined using a randomized block design of eight dietary sodium treatments (0.1, 0.4, 0.5, 0.66, 0.8, 1.2, 1.6 or 2.0 g Na/kg in a casein-lactalbumin-based purified diet) administered for periods of 4 wk. A total of 35 adult specific-pathogen-free domestic shorthaired cats (26 males and 9 females, 1.5-3 y of age) was given an equilibration diet (2 g Na/kg) for 14 d before assignment (or reassignment) to the treatments. A total of 12 cats (8 males, 4 females) was randomly assigned to the lowest six levels of sodium, and four cats to the highest two sodium levels. Cats consuming the diet containing 0.1 g Na/kg had significantly elevated aldosterone concentration in plasma, and packed cell volume. In addition, these cats exhibited anorexia, body weight loss, reduced urinary specific gravity and sodium excretion, and had a negative sodium balance. However, adult cats did not develop polydypsia and polyuria reported in sodium-deficient kittens. Cats given the diet containing 0.66 g Na/kg did not have an increased packed cell volume, but aldosterone concentration in the plasma was significantly elevated. However, cats given diets containing >/=0.8 g Na/kg had plasma aldosterone concentrations +info)
Epithelial sodium channel regulated by aldosterone-induced protein sgk.
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Sodium homeostasis in terrestrial and freshwater vertebrates is controlled by the corticosteroid hormones, principally aldosterone, which stimulate electrogenic Na+ absorption in tight epithelia. Although aldosterone is known to increase apical membrane Na+ permeability in target cells through changes in gene transcription, the mechanistic basis of this effect remains poorly understood. The predominant early effect of aldosterone is to increase the activity of the epithelial sodium channel (ENaC), although ENaC mRNA and protein levels do not change initially. Rather, the open probability and/or number of channels in the apical membrane are greatly increased by unknown modulators. To identify hormone-stimulated gene products that modulate ENaC activity, a subtracted cDNA library was generated from A6 cells, a stable cell line of renal distal nephron origin, and the effect of candidates on ENaC activity was tested in a coexpression assay. We report here the identification of sgk (serum and glucocorticoid-regulated kinase), a member of the serine-threonine kinase family, as an aldosterone-induced regulator of ENaC activity. sgk mRNA and protein were strongly and rapidly hormone stimulated both in A6 cells and in rat kidney. Furthermore, sgk stimulated ENaC activity approximately 7-fold when they were coexpressed in Xenopus laevis oocytes. These data suggest that sgk plays a central role in aldosterone regulation of Na+ absorption and thus in the control of extracellular fluid volume, blood pressure, and sodium homeostasis. (+info)
Primary aldosteronism with aldosterone-producing adrenal adenoma in a pregnant woman.
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A 30-year-old pregnant woman complained of muscle weakness at 29 weeks' gestation. She was hypertensive with severe hypokalemia. Lower plasma renin activity and higher aldosterone level than the normal values in pregnancy suggested primary aldosteronism. A cesarean delivery was performed at 31 weeks' gestation because of pulmonary congestion. The neonatal course was uncomplicated. The laparoscopic adrenalectomy for a 2.0-cm right adrenal adenoma resulted in normalizing of her blood pressure and serum potassium level. Although primary aldosteronism is rare, especially during pregnancy, it should be always considered as one of etiologies of hypertension in pregnancy. (+info)
Aldosterone, not estradiol, is the physiological agonist for rapid increases in cAMP in vascular smooth muscle cells.
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BACKGROUND: Steroid-induced gene regulation in the endocrine tissues and vascular wall is achieved through the interaction of specific receptor proteins and promoters of target genes. In addition to these delayed steroid actions, rapid effects of steroids have been reported in various tissues that were clearly incompatible with the classic theory of genomic steroid action. METHODS AND RESULTS: Because high doses of 17beta-estradiol have been shown to modulate intracellular cAMP levels in vascular smooth muscle cells, steroid-induced stimulation of adenylate cyclase stimulation and phosphorylation of cAMP response element binding protein was investigated in porcine coronary artery vascular smooth muscle cells. Aldosterone induces a approximately 1.5- to 2.5-fold increase in intracellular cAMP levels (EC50 approximately 0.01 to 0.1 nmol/L) within 1 minute, whereas 17beta-estradiol and hydrocortisone act only at supraphysiological concentrations (10 micromol/L). Aldosterone-induced changes in intracellular cAMP are calcium dependent; they are not blocked by inhibitors of mineralocorticoid receptors, transcription, or protein synthesis. In addition, aldosterone induces a time-dependent phosphorylation of cAMP response element binding protein with potential transcriptional importance. CONCLUSIONS: A nongenomic modulation of vascular smooth muscle cells by aldosterone is consistent with the data that aldosterone, not estrogen, is the physiological stimulus for cAMP. (+info)
Comparison of two aquaretic drugs (niravoline and OPC-31260) in cirrhotic rats with ascites and water retention.
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kappa-Opioid receptor agonists (niravoline) or nonpeptide antidiuretic hormone (ADH) V2 receptor antagonists (OPC-31260) possess aquaretic activity in cirrhosis; however, there is no information concerning the effects induced by the chronic administration of these drugs under this condition. To compare the renal and hormonal effects induced by the long-term oral administration of niravoline, OPC-31260, or vehicle, urine volume, urinary osmolality, sodium excretion, and urinary excretion of aldosterone (ALD) and ADH were measured in basal conditions and for 10 days after the daily oral administration of niravoline, OPC-31260, or vehicle to cirrhotic rats with ascites and water retention. Creatinine clearance, serum osmolality, ADH mRNA expression, and systemic hemodynamics were also measured at the end of the study. Niravoline increased water excretion, peripheral resistance, serum osmolality, and sodium excretion and reduced creatinine clearance, ALD and ADH excretion, and mRNA expression of ADH. OPC-31260 also increased water metabolism and sodium excretion and reduced urinary ALD, although the aquaretic effect was only evident during the first 2 days, and no effects on serum osmolality, renal filtration, and systemic hemodynamics were observed. Therefore, both agents have aquaretic efficacy, but the beneficial therapeutic effects of the long-term oral administration of niravoline are more consistent than those of OPC-31260 in cirrhotic rats with ascites and water retention. (+info)