Action of (1-des(aspartic acid), 8-isoleucine) angiotensin II upon the pressor and steroidogenic activity of angiotensin II.

The vascular and steroidogenic responses to (1-Sarcosine, 8-Isoleucine)-, and to (1-Des (Aspartic acid), 8-Isoleucine) angiotensin II were compared in bilaterally nephrectomized, ACTH-suppressed dogs receiving constant infusions of angiotensin II. Aldosterone secretion rate was significantly inhibited by pretreatment with 200 ng/Kg/min of the heptapeptide, (1-Des(Aspartic acid), 8-Isoleucine) ang II, but not by similar doses of the octapeptide, (1-Sarcosine, 8-Isoleucine) ang II. In contrast, the pressor action of ang II was unaffected by (1-Des (Aspartic acid), 8-Isoleucine) ang II though significant inhibition occurred with relatively small doses of (1-Sarcosine, 8-Isoleucine) ang II. This study suggests that: (a) angiotensin receptors in adrenal cortex and vascular smooth muscle are functionally different, and (b) (1-Des(Aspartic acid),8-Isoleucine) angiotensin II is a specific antagonist of steroidogenic effect of ang II.     

Biological activity of des-asp1-angiotensin II (angiotensin III) in man.

Effects of des-asp1-angiotensin II (angiotensin III) on blood pressure and aldosterone secretion were examined in man. Angiotensin III was equipotent with val5-angiotensin II amide in the stimulation of aldosterone production, but had only 20% of the pressor activity of the later. These results are consistent with those previously reported by other investigators in animals.     

Regulation of sodium balance and blood pressure by the AT(1A) receptor for angiotensin II

To examine the role of the angiotensin II (AT)(1A) receptor in the regulation of blood pressure and sodium balance, we measured systolic blood pressure responses in AT(1A) receptor-deficient (Agtr1a-/-) and wild-type (Agtr1a+/+) mice while dietary sodium content was systematically altered. On a 0.4% sodium diet, systolic blood pressures were significantly lower in Agtr1a-/- than in +/+ mice. In Agtr1a+/+ mice, changing dietary sodium content did not affect blood pressure. In contrast, when Agtr1a-/- mice were fed a high-salt diet (6% NaCl), their systolic blood pressures increased significantly from 79+/-4 to 94+/-4 mm Hg (P<0.006). The low blood pressures of Agtr1a-/- mice decreased further while on a low-salt diet from 82+/-3 to 69+/-3 mm Hg (P<0.03). On the high-salt diet, urinary sodium excretion increased to similar levels in Agtr1a+/+ and -/- mice. Although urinary sodium excretion was substantially reduced in both groups during the low-salt diet, cumulative sodium balances became negative in Agtr1a-/- mice despite a 6-fold increase in urinary aldosterone. We infer, therefore, that the reduced blood pressures in Agtr1a-/- mice on a normal diet are caused by depletion of sodium and extracellular volume. Their "sodium sensitivity" suggests a critical role for renal AT(1A) receptors to modulate sodium handling.     

Regulation of blood pressure by the type 1A angiotensin II receptor gene.

The renin-angiotensin system plays a critical role in sodium and fluid homeostasis. Genetic or acquired alterations in the expression of components of this system are strongly implicated in the pathogenesis of hypertension. To specifically examine the physiological and genetic functions of the type 1A receptor for angiotensin II, we have disrupted the mouse gene encoding this receptor in embryonic stem cells by gene targeting. Agtr1A(-/-) mice were born in expected numbers, and the histomorphology of their kidneys, heart, and vasculature was normal. AT1 receptor-specific angiotensin II binding was not detected in the kidneys of homozygous Agtr1A(-/-) mutant animals, and Agtr1A(+/-) heterozygotes exhibited a reduction in renal AT1 receptor-specific binding to approximately 50% of wild-type [Agtr1A(+/+)] levels. Pressor responses to infused angiotensin II were virtually absent in Agtr1A(-/-) mice and were qualitatively altered in Agtr1A(+/-) heterozygotes. Compared with wild-type controls, systolic blood pressure measured by tail cuff sphygmomanometer was reduced by 12 mmHg (1 mmHg = 133 Pa) in Agtr1A(+/-) mice and by 24 mmHg in Agtr1A(-/-) mice. Similar differences in blood pressure between the groups were seen when intraarterial pressures were measured by carotid cannulation. These studies demonstrate that type 1A angiotensin II receptor function is required for vascular and hemodynamic responses to angiotensin II and that altered expression of the Agtr1A gene has marked effects on blood pressures.     

Actions of angiotensin II antagonists upon aldosterone production by isolated adrenal glomerulosa cells.

The biological activities of angiotensin II antagonists upon basal and angiotensin II-stimulated aldosterone production were evaluated in an isolated canine glomerulosa cell preparation. The most potent competitive antagonist of angiotensin II-stimulated aldosterone production was the [Sar1, Ile8]derivative of angiotensin II. However, this peptide was also a partial agonist at concentrations required to inhibit the steroidogenic effect of angiotensin II on dog adrenal cells, and never reduced aldosterone production to basal levels. On a molar basis, the [Sar1, Ala8] and [Sar1, Gly8]derivatives of angiotensin II were relatively less potent as competitive inhibitors of angiotensin II-stimulated aldosterone production. However, the [Ala8] and [Gly8]-analogues did not exhibit significant agonist activity and were therefore more effective antagonists of angiontensin II-stimulated aldosterone production. These results suggest that increased length of the aliphatic side chain at the C-terminus of angiotensin II antagonists is accompanied by enhanced affinity for the receptor site, but also by increased agonist activity upon aldosterone synthesis. The actions of angiotensin II and [Des-Asp1]angiotensin II upon aldosterone production were inhibited identically and completely by [Sar1, Ala8]angiotensin II, and identically, though incompletely, by lower concentrations of [Sar1, Ile8]angiotensin II. The heptapeptide antagonist [Des-Asp1, Ile8]angiotensin II was much less potent than [Sar1, Ile8]angiotensin II as an inhibitor of the actions of both the heptapeptide and octapeptide agonists. The antagonist activity of six angiotensin II analogues at the adrenal level, determined by the concentration required for 50% inhibition of maximum aldosterone secretion, correlated well with their antagonist activity measured upon isolated smooth muscle. These observations demonstrate that the octapeptide antagonists are more effective than the heptapeptide antagonists upon angiotensin II-stimulated aldosterone production, and that angiotensin II receptors in smooth muscle and adrenal cortex exhibit generally similar responses to angiotensin II antagonists. Also, these results do not support the proposal that the [Des-Asp1]heptapeptide is an important intermediate in the action of angiotensin II upon adolesterone production in the adrenal glomerulosa cells. The production of aldosterone by dispersed zona glomerulosa cells in vitro provides a highly sensitive and biologically appropriate response for evaluation of the agonist and antagonist properties of angiotensin II analogues upon the adrenal gland.     

The effects of intravenous angiotensin II upon blood pressure and sodium and urate excretion in human pregnancy

Twelve women in their first 3 months of pregnancy received an i.v. saline load (3 mmol sodium/kg) and a graded infusion of angiotensin II (Ang II; i.e. 4, 8 and 16 ng/kg per min). As controls, twelve comparable pregnant subjects received the saline infusion alone. Eight non-pregnant women underwent both protocols, with doses of 2, 4 and 8 ng/kg per min Ang II, and thus acted as their own controls. Saline loading evoked proportionately similar falls in basal plasma renin (PRC) and plasma aldosterone (PAC) concentrations in pregnant and non-pregnant women. Angiotensin II evoked a dose-dependent pressor response, a graded increase in PAC and a reduction in sodium and urate excretion in both pregnant and non-pregnant women. The administration of Ang II had a proportionately greater effect on sodium and urate excretion in non-pregnant than in pregnant women; the pressor response to Ang II was also decreased in the pregnant women. The stimulation of PAC by Ang II, however, did not differ between the two groups. These results show that refractoriness to the renal and vascular effects of Ang II is present as early as the eleventh week of gestation. They also support the hypothesis that there is a degree of dissociation between the renin-angiotensin system and PAC in normal pregnancy.     

Blood pressure and plasma angiotensin II concentration after renal artery constriction and angiotensin infusion in the dog. (5-Isoleucine)angiotensin II and its breakdown fragments in dog blood.

We measured arterial plasma angiotensin II concentration, renal blood flow, and arterial blood pressure in six conscious dogs during intravenous infusion of angiotensin II (5, 10, and 20 ng/kg per min). The same measurements were made on a different occasion in the same six animals, while they were conscious, before and during constriction of a main renal artery. Arterial blood pressure and plasma angiotensin II rose and renal blood flow decreased in both experiments. The similarity of regressions for plasma angiotensin II concentration and arterial blood pressure in the two experiments strongly suggests that the rise of circulating angiotensin II after renal artery constriction is sufficient to account for the hypertension by its direct pressor action. As discussed, a different mechanism seems likely to be involved in the later stages of renal hypertension. Angiotensin II is more likely to be in the 5-isoleucine form than in the 5-valine form in the dog. In contrast to the rat, plasma concentrations of the heptapeptide (angiotensin III), hexapeptide, and pentapeptide fragments of angiotensin II are low in the dog.     

Angiotensin III stimulates aldosterone secretion from adrenal gland partially via angiotensin II type 2 receptor but not angiotensin II type 1 receptor

Angiotensin II (Ang II) and Ang III stimulate aldosterone secretion by adrenal glomerulosa, but the angiotensin receptor subtypes involved and the effects of Ang IV and Ang (1-7) are not clear. In vitro, different angiotensins were added to rat adrenal glomerulosa, and aldosterone concentration in the medium was measured. Ang II-induced aldosterone release was blocked (30.3 ± 7.1%) by an Ang II type 2 receptor (AT2R) antagonist, PD123319. Candesartan, an Ang II type 1 receptor (AT1R) antagonist, also blocked Ang II-induced aldosterone release (42.9 ± 4.8%). Coadministration of candesartan and PD123319 almost abolished the Ang II-induced aldosterone release. A selective AT2R agonist, CGP42112, was used to confirm the effects of AT2R. CGP42112 increased aldosterone secretion, which was almost completely inhibited by PD123319. In addition to Ang II, Ang III also induced aldosterone release, which was not blocked by candesartan. However, PD123319 blocked 22.4 ± 10.5% of the Ang III-induced aldosterone secretion. Ang IV and Ang (1-7) did not induce adrenal aldosterone secretion. In vivo, both Ang II and Ang III infusion increased plasma aldosterone concentration, but only Ang II elevated blood pressure. Ang IV and Ang (1-7) infusion did not affect blood pressure or aldosterone concentration. In conclusion, this report showed for the first time that AT2R partially mediates Ang III-induced aldosterone release, but not AT1R. Also, over 60% of Ang III-induced aldosterone release may be independent of both AT1R and AT2R. Ang III and AT2R signaling may have a role in the pathophysiology of aldosterone breakthrough.     

Effects of proopiomelanocortin peptides and angiotensin II on steroidogenesis in isolated aldosteronoma cells

Cells isolated from five aldosterone-producing adenomas were used to study glucocorticoid and aldosterone production in response to ACTH, angiotensin II (A II), and peptides derived from proopiomelanocortin (POMC), viz. the 16K N-terminal fragment (16K) and its derivative, gamma 3MSH and the C-terminal fragment beta-lipotropin (beta LPH) and its derivative beta-endorphin. At concentrations similar to those of ACTH and A II (10(-12)-10(-10) M), 16K, gamma 3MSH, and beta LPH selectively stimulated aldosterone production, which reached levels close to those obtained with A II. ACTH, however, was the most effective stimulant of steroidogenesis. The 16K, gamma 3MSH, and beta LPH peptides potentiated the action of ACTH, particularly in the case of aldosterone production. beta-Endorphin, whether used alone or in association with ACTH, had no effect on steroidogenesis at the dose used (10(-10) M). The principal glucocorticoid products of the adenoma cells were cortisol and corticosterone. The ratios of corticosterone to cortisol (B/F) and aldosterone to corticosterone (A/B) varied considerably from one adenoma to another, both basally and in response to ACTH. Nevertheless, within individual adenomas, the mean B/F ratio induced by ACTH [0.280 +/- 0.013 (+/- SEM)] was significantly larger than that induced by A II (0.127 +/- 0.007; P less than 0.001). By contrast, the A/B ratio in response to ACTH (0.061 +/- 0.003) was significantly smaller than that in response to A II (0.159 +/- 0.010; P less than 0.001). The values obtained with 16K (B/F, 0.106 +/- 0.010; A/B, 0.192 +/- 0.028) and gamma 3MSH (B/F, 0.122 +/- 0.012; A/B, 0.178 +/- 0.020) were close to those obtained with A II. 16K and gamma 3MSH potentiated ACTH's effect on steroidogenesis mainly by increasing the A/B ratio from 0.061 +/- 0.003 for ACTH alone to 0.100 +/- 0.008 for 16K plus ACTH (P less than 0.005) and to 0.092 +/- 0.005 for gamma 3MSH plus ACTH (P less than 0.001). The findings suggest that the stimulation of aldosterone production by 16K and gamma 3MSH in aldosteronoma cells is of the A II type and that these peptides may play a role in the genesis of primary aldosteronism.     

Changes in responses of blood pressure and several hormones to infusions of angiotensin II and angiotensin III in patients with essential hypertension

In this study, the effects of angiotensin II (A II, Asn-Arg-Val-Tyr-Val-His-Pro-Phe) and angiotensin III (A III, Arg-Val-Tyr-Ile-His-Pro-Phe) on blood pressure (B.P.), pulse rate, several hormones [plasma renin activity (PRA), plasma aldosterone (PA), ACTH, plasma cortisol (PC), urinary catecholamines and urinary aldosterone] and urinary electrolytes were investigated in 9 male patients with essential hypertension [mean age 36.2 +/- 4.1 (S.E.) years]. A II and A III infusions (8 ng/kg/min, 60 min) were started from 0900 h and blood samples were drawn before, at 15, 30, 45, 60 min after the beginning of the infusions, and at 15 min after their cessation. Urinary samples were collected within 2 hrs before and after the infusions, respectively. A II significantly increased B.P.(p less than 0.01) during the infusions, whereas A III did not increase B.P.. PRA significantly decreased after the infusions of A II and A III (p less than 0.05), but the potency of A II was significantly greater than that of A III (p less than 0.01). PA was increased after both infusions, but in response to A III, a peak was observed at 30 min after the infusion and subsequently, the levels decreased gradually. Significant differences between both responses were found at 45 and 60 min (p less than 0.05) after the infusions. ACTH was unchanged during the infusions, but PC was equipotentially suppressed during the infusions, with the suppression of A II being similar to that of A III. In the responses of urinary catecholamines, noradrenaline and dopamine were equipotentially decreased after the infusions (p less than 0.05). The results of the present study clearly indicate that several differences exist between the biological activities of A II and those of A III. Further systematic experimental studies are needed to resolve the details.     

A/C1166 gene polymorphism of the angiotensin II type 1 receptor (AT1) and ambulatory blood pressure: the Ohasama Study.

We previously investigated the relation between hypertension and each of three major genetic polymorphisms in the renin-angiotensin (AGT)-aldosterone system (R-A-A), AGT M235T, angiotensin convert enzyme (ACE) I/D, and CYP11B2 -344C/T, by means of ambulatory blood pressure (ABP) monitoring in a general Japanese population (the Ohasama Study). A/C1166 gene polymorphism in the 3' untranslated region of the angiotensin II type 1 receptor (AT1) gene is the final remaining major target in R-A-A to be examined in the Ohasama Study population. In the present study, the AT1 A/C1166 polymorphism was genotyped by the TaqMan polymerase chain reaction (PCR) method or restriction fragment length polymorphism (RFLP) in 802 Japanese subjects aged 40 and over, who were previously genotyped for the AGT M235T, ACE D/I, CYP11B2 -344C/T polymorphisms. The AA genotype, AC genotype, and CC genotype were present in 678 (84.5%), 121 (15.1%), and 3 (0.4%) of subjects, respectively. Since the frequency of the C allele was quite low (0.079), the genotypes were classified according to the presence or absence of the C allele. Although daytime blood pressure (BP) was higher in subjects with the C allele, the difference was not statistically significant after adjusting for age, gender, body mass index, and smoking status. No significant difference was noted in the prevalence of cardiovascular diseases or nocturnal BP decline between the two groups. These results indicated that AT1 A/C1166 polymorphism was not associated with any clinical parameters associated with hypertension or atherosclerosis in the Japanese population.     

Long-term effects of ACTH combined with angiotensin II on steroidogenesis and adrenal zona glomerulosa morphology in the rat

To test the hypothesis that the trophic action of angiotensin II on the adrenal zona glomerulosa may allow a sustained stimulation of aldosterone by ACTH by preventing the morphological changes of the zona glomerulosa cells into zona fasciculata-like elements we investigated the effects in rats of a 6-day treatment with ACTH (100 micrograms/kg/day) alone or combined with angiotensin II (300 ng/kg/day) on corticosterone and aldosterone production and adrenal morphology. The responsiveness of both steroids to an acute ACTH dose was also studied on the last day of long-term treatment. Morphologic data showed that prolonged ACTH treatment stimulated the growth of zona glomerulosa cells, though it transformed the tubulo-lamellar cristae of mitochondria into a homogeneous population of vesicles. Angiotensin II furthered the trophic effects of ACTH but prevented the mitochondrial transformation. Despite its ability to conserve the well differentiated aspect of the zona glomerulosa cells, the administration of angiotensin II was unable to prevent the fall in the secretion of aldosterone caused by chronic ACTH treatment and its subsequent unresponsiveness to ACTH stimulation.     

Studies on cyclic nucleotides in the adrenal gland. VIII. Effects of angiotensin on adenosine 3',5'-monophosphate and steroidogenesis in the adrenal cortex.

Effects of angiotensin II on corticoid biogenesis and cAMP levels in the zona fasciculata-reticularis (the decapsulated fraction) and the zona glomerulosa (the capsular fraction) from the rat adrenal gland have been studied. Angiotensin II exclusively stimulated steroidogenesis in the zona glomerulosa without stimulation of the cAMP system, suggesting that steroidogenic action of this polypeptide does not involve the adenylate cyclase system. Angiotensin II was also found to stimulate cAMP-phosphodiesterase activity in the zona glomerulosa. An elevation of calcium concentration in the incubation medium has been observed to be effective in stimulating the production of aldosterone and cAMP by the capsular fraction. Angiotensin II caused a significant enhancement of the steroidogenic response of the capsular fraction to increasing calcium concentration regardless of the response of the cAMP system to calcium. This steroidogenic effect of angiotensin II was completely abolished by calcium antagonists added to the incubation medium without any inhibitory effect on the calcium-induced accumulation of tissue cAMP. These results suggest that angiotensin II acts on the adrenal II acts on the adrenal glomerulosa cell to increase intracellular calcium, which in turn directly stimulates steroidogenesis concomitant with the increased activity of phosphodiesterase.