Plasma aldosterone and corticosterone responses to adrenocorticotropin, angiotensin, potassium, and stress in spontaneously hypertensive rats

The responses of plasma aldosterone and corticosterone to ACTH, angiotensin II (AII), and potassium chloride (KCl) infusion and the aldosterone, corticosterone and PRA responses to immobilization stress were studied in 2-month-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) normotensive controls. Basal levels of plasma aldosterone and corticosterone were greater and PRA was less in the SHR than in the WKY. Aldosterone and corticosterone responses to graded AII were similar in both groups. Aldosterone and corticosterone responses to graded doses of KCl and ACTH, however, were significantly greater in SHR than in WKY normotensive rats. Plasma corticosterone, PRA, and aldosterone responses to immobilization stress were reduced in SHR compared to WKY. At 2 months of age, blood pressure was definitely elevated in SHR and was associated with low PRA and relatively high basal levels of aldosterone and corticosterone. Discordance between the renin-angiotensin system and mineralocorticoid secretion in the SHR may be due to enhanced adrenal sensitivity to factors such as ACTH and potassium. Suppressed PRA in SHR may be due, in part, to increased mineralocorticoid secretion, resulting in sodium retention and intravascular volume expansion.     

Aldosterone breakthrough during angiotensin II receptor blockade in hypertensive patients with diabetes mellitus

BACKGROUND: Aldosterone is an important pathogenetic factor, independent of the renin-angiotensin system in cardiovascular and renal disease. Aldosterone breakthrough during angiotensin-converting enzyme (ACE) inhibitor therapy was reported in hypertension, diabetes mellitus, and chronic renal disease. It is unclear whether the angiotensin II receptor blocker (ARB) causes aldosterone breakthrough in patients with hypertension and diabetes mellitus, and whether aldosterone breakthrough contributes to renal injury in these patients. METHODS: We prospectively studied 95 hypertensive patients with diabetes mellitus. Patients were treated with candesartan (8 mg/day, n = 47) or valsartan (80 mg/day, n = 48) for 15 months. Blood pressure (BP), urinary albumin excretion (UAE), biochemical markers, plasma aldosterone concentration (PAC), and plasma renin activity (PRA) were measured before and at 3, 6, 12, and 15 months of treatment. Nine patients who exhibited aldosterone breakthrough after treatment with ARB were placed on spironolactone (25 mg/day) for 3 months, and BP, UAE, and biochemical markers were measured after treatment. RESULTS: Although the overall PAC was significantly decreased (P < .05) in each group, it eventually increased in 21 (candesartan, 11 patients; valsartan, 10 patients) of 95 patients (22%; aldosterone breakthrough). Blood pressure, PRA, and biomedical markers did not differ between the two groups during treatment. Although UAE was significantly decreased in patients with or without aldosterone breakthrough at 6 months, it was increased again at 15 months of treatment in patients with aldosterone breakthrough. Treatment with spironolactone markedly reduced UAE in these patients. CONCLUSIONS: Aldosterone breakthrough was seen to be equal in hypertensive patients with diabetes mellitus treated with candesartan or valsartan. Aldosterone blockade therapy may be effective in preventing renal injury in hypertensive patients with aldosterone breakthrough.     

Potassium homeostasis in chronic experimental diabetes mellitus in rats

To examine potassium homeostasis in diabetes mellitus, we observed the effect of dietary potassium loading on the renin-angiotensin-aldosterone system and potassium balance in streptozotocin-induced diabetic rats. In diabetic rats with 26.51 +/- 1.89 mmol/l of serum glucose, the plasma renin activity (PRA), plasma aldosterone (PA), immunoreactive insulin (IRI) and urinary excretion of prostaglandin E2 (PGE2) were all significantly lower than in control rats, but the plasma potassium and renal function were not significantly different. With potassium loading, both control and diabetic rats showed a similar increase in plasma potassium and urinary potassium excretion and a decrease in PRA, but the IRI, plasma corticosterone and urinary excretion of PGE2 exhibited no significant change. On the other hand, the PA was significantly increased only in the control rats, and not in the diabetic rats on potassium loading. Based up on these results, it is suggested that potassium homeostasis is well maintained in diabetic rats with normal renal function in spite of an attenuated response of aldosterone secretion to dietary potassium loading and insulin deficiency.     

Effects of angiotensin II, adrenocorticotropin, and potassium on aldosterone production in adrenal zona glomerulosa cells from streptozotocin-induced diabetic rats

Hyporeninemic hypoaldosteronism has been shown to occur in streptozotocin-induced chronic diabetic rats with normokalemia. To test the nature of the aldosterone deficiency, we investigated the responses of aldosterone production to angiotensin II (AII), ACTH, and potassium in adrenal zona glomerulosa cells from diabetic rats at 6 weeks after an injection of streptozotocin compared with those in the cells from control rats. In diabetic rats, plasma glucose was high and plasma immunoreactive insulin was low. Diabetic rats also had low levels of PRA and plasma AII, low levels of plasma aldosterone, and normal levels of plasma corticosterone and plasma potassium. The zona glomerulosa width was narrower in diabetic rats than in control rats. Basal aldosterone production, when corrected to an uniform number of cells per group, was similar in the cells from control and diabetic rats. Cells from diabetic rats showed a less sensitive and lower response of aldosterone production to AII, increases in the threshold and the ED50, and a decrease in the maximal AII-stimulated aldosterone level. ACTH, however, caused a similar effect on aldosterone production in the cells from control and diabetic rats. Cells from diabetic rats exhibited a less sensitive response of aldosterone production to potassium and a tendency to be low in the maximal potassium-stimulated aldosterone level, presumably attributable to the impairment of adrenal zona glomerulosa cells to AII. We conclude that the hypoaldosteronism observed in our diabetic rats may be secondary to the deficiency of AII.     

Effect of upright posture on the aldosterone responses to dopamine, metoclopramide, angiotensin II, and adrenocorticotropin

Aldosterone secretion in man is stimulated by potassium (K), ACTH, and angiotensin II (AII) and inhibited by dopamine (DA). In normal sodium-replete supine individuals, aldosterone secretion is under maximum tonic inhibition by DA and is not inhibited further by DA administration. Sodium depletion alters plasma aldosterone responses to secretogogues. Upright posture, another physiological stimulus to aldosterone secretion, recently was demonstrated to sensitize the adrenal cortex to inhibition of aldosterone secretion by a large quantity of DA (4.0 micrograms/kg X min). The effect of upright posture on aldosterone responses to other secretogogues is unknown. In this study, we investigated the effect of upright posture on aldosterone responses to low infusion rates of DA, to the DA antagonist metoclopramide (M) and to AII and ACTH. Fourteen normal men eating a normal sodium diet were studied. In eight, PRA, plasma aldosterone (PAC), plasma cortisol (F), and serum K concentrations were determined after 4 h of upright posture and infusion of vehicle (D5W) or DA at 0.1, 0.4, and 2.0 micrograms/kg X min. Six other normal men were kept supine for 3 h and, on separate days, upright for 3 h and given iv M (10-mg bolus dose), AII (1 and 4 pmol/kg X min for 30 min), and ACTH (20 and 120 mU/h for 30 min). PAC, PRA, F, and K were measured before and after these three secretogogues were administered. In the presence of vehicle, mean PAC increased by 15.1 +/- 4.3 (+/- SEM) ng/dL after 4 h of upright posture. In the presence of DA infused at 0.1, 0.4, and 2.0 micrograms/kg X min, the PAC response to upright posture was decreased to 9.7 +/- 2.5 (P = NS), 7.5 +/- 3.9 (P less than 0.05), and 8.1 +/- 2.0 (P less than 0.05) ng/dL, respectively. This occurred without a decrease in PRA, F, or K. The stimulation of PAC 10 and 20 min after a 10-mg bolus dose of M was 9.6 +/- 3.3 and 9.3 +/- 2.6 ng/dL, respectively, in supine subjects and 8.3 +/- 2.3 and 10.8 +/- 3.4 ng/dL 10 and 20 min after the M dose in upright subjects. The responses of PAC to ACTH and AII also were unchanged after 3 h of upright posture. We conclude that upright posture sensitizes the adrenal cortex to inhibition of aldosterone secretion by DA without affecting other modifiers of aldosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Aldosterone enhances angiotensin II receptor binding and inositol phosphate responses.

Clinical states in which angiotensin II is increased are often associated with increases in mineralocorticoids. To determine the effects of mineralocorticoids on angiotensin II action, we examined the effects of aldosterone on angiotensin II receptor expression and function in cultured rat vascular smooth muscle cells. Incubation with aldosterone resulted in concentration- and time-dependent increases in angiotensin II receptor number, without changes in binding affinity. For example, incubation with 1 microM aldosterone for 40 hours resulted in 59% increases in angiotensin II receptor number. Increases in angiotensin II receptors were dependent on protein synthesis as evidenced by the time dependency of upregulation and inhibition by cycloheximide. Incubation with aldosterone resulted in enhanced angiotensin II-stimulated phospholipase C activation, as demonstrated by increases in angiotensin II-induced inositol phosphate responses in proportion to the increases in receptor number. In addition, aldosterone prevented angiotensin II-induced downregulation of angiotensin II surface receptors and angiotensin II desensitization of inositol phosphate formation. In summary, aldosterone 1) directly increased angiotensin II receptor number, 2) increased angiotensin II-stimulated inositol phosphate responses, and 3) prevented angiotensin II-induced downregulation and desensitization. In conclusion, aldosterone may potentiate the pressor responses of angiotensin II via effects on angiotensin II receptors.     

The role of adrenocorticotropin in the cortisol and aldosterone responses to angiotensin II in conscious dogs

The role of ACTH in the cortisol and aldosterone responses to iv angiotensin II (AII) infusion, (5, 10, and 20 ng kg-1 min-1) in dogs was evaluated by examining the effect of AII infusion in conscious dogs pretreated with dexamethasone to suppress endogenous ACTH secretion. AII infusion in untreated dogs produced dose-related increases in plasma cortisol and aldosterone concentrations. The plasma ACTH concentration also increased. Dexamethasone treatment lowered the basal cortisol concentration from 1.7 +/- 0.1 to 0.7 +/- 0.1 micrograms/dl (P less than 0.05) and the ACTH concentration from 52 +/- 3 to 41 +/- 4 pg/ml (P less than 0.05), and abolished the cortisol response to all doses of AII, indicating that ACTH was necessary for the response. On the other hand, the basal aldosterone concentration was not significantly affected by dexamethasone, although the aldosterone response to the highest dose of AII was reduced. Additional experiments were performed to determine if the cortisol and aldosterone responses to AII (20 ng kg-1 min-1) in dexamethasone-treated dogs are restored if the ACTH concentration is maintained near control levels by iv infusion of synthetic alpha ACTH-(1-24) (0.3 ng kg-1 min-1). AII still failed to increase the plasma cortisol concentration in this group of dogs; however, the aldosterone response was fully restored. To evaluate the effect of elevated ACTH levels on the steroidogenic effects of AII, dogs were treated with dexamethasone and a higher dose of ACTH (0.4 ng kg-1 min-1). This dose of ACTH increased the plasma cortisol concentration from 1.7 +/- 0.1 to 3.5 +/- 0.8 micrograms/dl (P less than 0.05), but did not significantly affect the plasma aldosterone concentration. In the presence of constant elevated levels of ACTH, AII (10 and 20 ng kg-1 min-1) increased the plasma cortisol concentration in dexamethasone-treated dogs, although the response to the 10 ng kg-1 min-1 dose was smaller than the response in untreated dogs. Infusion of AII at 5 ng kg-1 min-1 did not increase the plasma cortisol concentration. In contrast, the increased plasma aldosterone produced by AII infusion in dexamethasone-treated dogs was not altered in the presence of elevated ACTH levels. Finally, AII infusion did not alter the clearance of cortisol. Collectively, these results demonstrate that an increase in plasma ACTH is necessary for the cortisol response to AII infusion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intracerebroventricular atrial natriuretic peptide infusion augments the adrenocorticotropin and angiotensin II responses to hemorrhage in sheep

The central actions of atrial natriuretic peptide (ANP) in rats include inhibition of arginine vasopressin (AVP) release, and less consistently, ACTH suppression and hypotension. To explore any such inhibitory actions on basal and stimulated levels of AVP and ACTH, we have studied the effect of intracerebroventricular (ICV) infusion of ANP on the hemodynamic and hormonal response to acute hemorrhage in conscious sheep. Two groups of 5 sheep received rat ANP(101-126) by ICV infusion (0.5 microgram bolus followed by 0.5 microgram/h for 3 h, or 5 micrograms bolus followed by 5 micrograms/h for 3 h) as well as artificial cerebrospinal fluid control infusions in random order. One hour after the start of the ICV infusion, acute hemorrhage (15 ml/kg BW within 10 min) was performed. Basal levels before hemorrhage of mean arterial pressure (MAP), heart rate and plasma hormones were unaltered by either dose of ICV ANP. After hemorrhage, the fall in MAP and rise in heart rate were similar in each group. However, compared to control infusions the response to hemorrhage of ACTH (433 +/- 147 to 2,175 +/- 588 vs. control 541 +/- 103 to 893 +/- 244 ng/l; p less than 0.016) and angiotensin II (AII) (18 +/- 3 to 94 +/- 23 vs. control 18 +/- 4 to 58 +/- 8 pmol/l; p less than 0.001) were significantly greater during high-dose ANP infusion. Although peak AVP levels more than doubled those observed on the control day, the increase did not reach statistical significance (p less than 0.1053). Plasma concentration of cortisol, aldosterone, epinephrine and norepinephrine were not significantly different in control and ANP-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gradual reactivation of vascular angiotensin I to angiotensin II conversion during chronic ACE inhibitor therapy in patients with diabetes mellitus

Aims/hypothesis In chronic heart failure there is gradual reactivation of vascular tissue angiotensin I (AI) to angiotensin II (AII) conversion over time in patients taking chronic ACE inhibitor therapy. However, it remains unknown whether the same overall phenomenon occurs in other patients taking chronic ACE inhibitor therapy, such as patients with type 2 diabetes mellitus. Methods We studied 30 patients with type 2 diabetes mellitus (mean age 43.5 ± 10.8 years), all of whom received lisinopril (20 mg/day) as part of their normal treatment. Over the course of the 18 month study, we made measurements at 0, 9 and 18 months. These measurements included plasma values for components of the renin–angiotensin–aldosterone system. In addition, we infused AI and AII into the brachial arteries of patients to assess vascular tissue AI to AII conversion. Results There were no significant changes in plasma renin activity, ACE, AI, AII or aldosterone during the study. In contrast, vascular AI to AII conversion was significantly (p = 0.01) greater at 18 months than at 0 months. There was no change over time in the response to infused AII. Conclusions/interpretation We have shown in vivo that vascular tissue AI to AII conversion gradually increases over time in patients with type 2 diabetes being treated with lisinopril. Further studies are required to determine whether this reactivation detracts from the cardioprotective effects of chronic ACE inhibitor therapy in diabetic patients, and if so, how best to overcome it.     

Impaired angiotensin II regulation of renal C-type natriuretic peptide mRNA expression in experimental diabetes mellitus

OBJECTIVE: Abnormalities in the regulation of natriuretic peptides (NP) associated with major diseases such as hypertension, heart failure, and diabetes mellitus (DM) have been reported. We investigated levels of mRNA for the vasodilator C-type natriuretic peptide (CNP) in the renal cortex of streptozotocin (STZ)-diabetic rats and the influence of an angiotensin II inhibition. METHODS: DM was induced in Wistar rats by a single STZ injection. Rats were kept for 12 weeks. Additionally, the influence of the ACE inhibitor ramipril (Ram: 3 mg/kg/day) and the AT1 receptor antagonist losartan (Los: 20 mg/kg/day) on CNP expression in the STZ-diabetic and control groups was studied (each group n=6). Animals were characterized by their mean arterial blood pressure, plasma glucose levels, and renal function (each group n=9). After extraction of total renal cortical RNA, CNP expression was analyzed by Northern blots. RESULTS: Renal function was impaired in STZ-diabetic rats which has been improved by Ram and Los treatment. Untreated STZ-diabetic rats showed no difference in renal CNP expression compared to untreated controls. Ram and Los treatments led to an increase in renal cortical CNP mRNA in both diabetic and non-diabetic rats. This effect was weaker in STZ-diabetic rats (Ram: control 5.4-fold, STZ 3.5-fold; Los: control 4.2-fold, STZ 1.9-fold). CONCLUSION: These results clearly demonstrate a direct regulatory effect of the renin-angiotensin system (RAS) on renal mRNA levels of CNP. We suggest that RAS inhibition not only prevents the generation of angiotensin II (AngII) but also leads to a stimulation of CNP expression. We conclude that AngII suppresses CNP expression via the AT1 receptor and this mechanism is impaired in STZ-diabetic rats.     

Diminished aldosterone responses to angiotensin II and adrenocorticotropin in hypocalcemic subjects: restoration of responsiveness with normocalcemia

ACTH-, angiotensin II (AII)-, and K+-mediated aldosterone responses in vitro are dependent on extracellular and intracellular Ca concentrations. This study examined in vivo the relationship of changes in ambient serum calcium (serum Ca) to ACTH- and AII-mediated aldosterone release in hypoparathyroid subjects. Plasma aldosterone (PA) responses to graded dose infusions of ACTH and AII were examined in hypoparathyroid (HypoPTH) patients before (n = 8) and after correction of hypocalcemia (n = 6) and compared to responses in 20 normotensive normocalcemic subjects. ACTH and AII were infused for 90 min at rates increasing from 12.5 to 50 mIU/30 min and 0.5 to 2.0 ng/kg X min, respectively. Pretreatment mean serum Ca was 6.8 +/- 0.2 (+/- SEM) mg/dl, and it rose to 9.3 +/- 0.2 mg/dl after 3-8 weeks of vitamin D administration. In the untreated HypoPTH patients, basal mean PA (5.4 +/- 1.3 ng/dl) was lower (P less than 0.01) than in the normal subjects (10.6 +/- 0.6 ng/dl) or treated HypoPTH patients (9.5 +/- 1.8 ng/dl). There was a marked reduction in PA responses to ACTH at all doses in the untreated HypoPTH patients compared to the normal subjects. With normalization of serum Ca in four patients, the mean peak PA response to ACTH (25.1 +/- 6.0 ng/dl) was not significantly different from normal (28.9 +/- 1.7 ng/dl). During graded dose AII infusion in five untreated HypoPTH patients, mean PA levels increased from 6.9 +/- 1.2 to 11.6 +/- 2.2 ng/dl; when the serum Ca was normal, the corresponding values were 8.7 +/- 1.8 and 20.2 +/- 3.61 ng/dl. There was a positive correlation (r = 0.475; P less than 0.05) between basal PA and serum Ca levels. In addition, maximum changes in mean arterial pressure in response to AII infusions were significantly greater after correction of hypocalcemia. These observations indicate that in HypoPTH patients, extracellular Ca concentrations can influence humoral aldosterone response to ACTH and AII and pressor responses to AII.     

Differential plasma beta-endorphin, beta-lipotropin, and adrenocorticotropin responses to stress in rats

This study was designed to compare the amounts of ACTH, beta-endorphin (beta END), and beta-lipotropin (beta LPH) that are present in plasma under basal conditions and after single and repeated administration of a discrete 2-min restraint stress both in intact and in chronically adrenalectomized rats. In intact rats, application of a 2-min restraint stress produced rapid parallel increases in plasma concentrations of radioimmunoassayable ACTH and beta END/beta LPH (the total of beta END-like immunoreactivities), with peaks 2.5-5 min after onset of the stress and return almost to basal concentrations by 30 min. Gel exclusion chromatography [Sephadex G-50 (fine)] and subsequent RIA revealed that plasma obtained from control nonstressed intact rats contained much greater quantities of beta END (94% of the total beta END/beta LPH immunoreactivity) than beta LPH. In contrast, equal amounts of beta END and beta LPH were present in plasma of intact rats 2.5-10 min after onset of the 2-min restraint stress. Chronically adrenalectomized rats lacking glucocorticoid-negative feedback had significantly higher basal plasma concentrations of beta END/beta LPH and ACTH than those present in intact rats. Furthermore, the plasma responses of both beta END/beta LPH and ACTH to stress were markedly enhanced in chronically adrenalectomized rats compared to the corresponding responses in intact rats. Gel exclusion chromatography revealed that both the higher basal concentration and the enhanced plasma beta END/beta LPH response to stress in adrenalectomized rats resulted primarily from increases in the beta LPH component, with lesser increases in the beta END component. In contrast to the proportion in intact rats, in chronically adrenalectomized rats, beta END represented about 27% of the total beta END/beta LPH immunoreactivity in the basal state and about 18% 5-10 min after the onset of restraint stress. In intact rats, the plasma ACTH responses to a subsequent stress applied 5 min (a time when peak plasma levels of hormones are present) or 30 min (a time when the plasma hormone concentrations have returned to prestress levels) after the initial stress and the plasma beta END/beta LPH response to a second stress applied at 30 min were equal to the corresponding hormone responses to a single stress. In contrast, the plasma beta END/beta LPH response to the subsequent stress applied 5 min after the initial stress was significantly potentiated in intact rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

Aldosterone in colonic potassium adaptation in rats

The influence of adrenalectomy and administration of aldosterone on potassium secretion by colonic epithelium was studied in vivo in rats, particularly in relation to potassium adaptation (induced by feeding a potassium-rich diet) and the response to acute i.v. administration of a potassium load. Adrenalectomy (rats maintained on dexamethasone and saline) impaired the development of potassium adaptation or considerably reduced it if the rats had been previously adapted. The partial adaptation observed in the adrenalectomized rats may be related to the increased plasma potassium concentration developed when these rats received the potassium-rich diet. Within 2 h of acute aldosterone administration, the response of the potassium secretion rate to acute potassium loading in adrenalectomized rats was significantly improved. When aldosterone (2 micrograms/day per 100 g body weight, given by osmotic minipump) was added to the replacement treatment, the plasma concentration of potassium was similar to that of the intact rats, and both potassium adaptation and the response to the acute potassium load were completely restored. Transepithelial potential difference and sodium transport were not stimulated, being similar to the values in intact rats. Considerable changes in potassium secretion induced by acute potassium loading did not significantly affect sodium transport. The findings suggest that the sodium and potassium epithelial pathways are, to a large extent, independently influenced by aldosterone. Aldosterone appears to be essential for complete adaptation and, in a relatively low dose, can completely restore potassium adaptation and the response to acute potassium loads in adrenalectomized rats.     

Aldosterone breakthrough during angiotensin II receptor antagonist therapy in stroke-prone spontaneously hypertensive rats

Aldosterone breakthrough during ACE inhibitor therapy has been reported. This study investigates changes in plasma aldosterone concentration (PAC) and its mechanism and effects on target organ damage during long-term angiotensin II type 1 (AT1) receptor antagonist (AT1A) therapy in hypertensive rats. An AT1A (candesartan, 1 mg/kg per day PO) was administered in stroke-prone spontaneously hypertensive rats from 4 weeks of age for 34 weeks. PAC was significantly decreased during the first 4 weeks but showed aldosterone breakthrough after 8 weeks of AT1A administration. Plasma angiotensin II concentration was significantly elevated, whereas no change was seen in plasma ACTH or serum potassium. The mechanism(s) of aldosterone breakthrough were investigated by giving high doses of candesartan (3 mg/kg per day PO), dexamethasone (200 microg/kg per day IP), or the AT2 antagonist (PD123319, 10 mg/kg per day SC) during the last week of the 24-week AT1A treatment period. Dexamethasone and AT2 antagonist but not high-dose AT1A produced a significant decrease in PAC, with a larger decrease produced by the AT2 antagonist. To clarify the effects of the residual aldosterone, effects of coadministration of low-dose spironolactone (10 mg/kg per day SC), an aldosterone antagonist, on left ventricular hypertrophy and expression of brain natriuretic peptide mRNA were determined. Low-dose spironolactone further improved left ventricular hypertrophy and brain natriuretic peptide mRNA expression despite no additional depressor effect. These results suggest that aldosterone breakthrough occurs during long-term AT1A therapy, mainly by an AT2-dependent mechanism. Residual aldosterone may attenuate the cardioprotective effects of AT1A.     

Aldosterone receptor antagonism reduces urinary C-reactive protein excretion in angiotensin II–infused,hypertensive rats

Elevated C-reactive protein (CRP) may contribute to elevated arterial pressure in angiotensin (Ang) II–dependent hypertension. However, the in vivo effects of Ang II and of mineralocorticoid receptor (MR) antagonism on CRP during Ang II–dependent hypertension have not been examined. In addition, urinary CRP excretion as a method to monitor the progression of Ang II–induced inflammation has not been evaluated. Urine samples were collected from 3 groups (n = 10/group) of rats: normotensive control, Ang II–infused (60 ng/minute), and Ang II + eplerenone (epl; 25 mg/day). A diet containing epl (0.1%) was provided after 1 week of Ang II infusion. After 28 days, Ang II increased systolic blood pressure (SBP) from 136 ± 5 to 207 ± 8 mm Hg; this response in SBP was not altered after MR antagonism (215 ± 6 mm Hg). Ang II infusion increased plasma CRP from 14 ± 2 to 26 ± 3 μg/mL and increased urinary immunoreactive CRP (irCRP) excretion nearly 8-fold (143 ± 26 vs. 1102 ± 115 ng/day). Treatment with eplerenone reduced plasma CRP by 25% and urinary irCRP by 34% in Ang II–infused rats, suggesting that aldosterone contributes to the CRP-associated inflammatory response in Ang II–dependent hypertension. The increase in SBP preceded the increase in irCRP excretion by at least 4 days, suggesting that CRP does not significantly contribute to increased arterial BP in Ang II–dependent hypertension. The blockade of MR reduced plasma CRP and urinary irCRP excretion, demonstrating the contribution of aldosterone to the Ang II–induced generation of CRP. Furthermore, urinary CRP may serve as a noninvasive index for monitoring cardiovascular inflammation during hypertension.     

Placental ultrastruct in rats with experimental diabetes mellitus

The placenta of Wistar rats with various forms of diabetes mellitis was studied by electron microscopy. Metabolic disturbances characteristic of alloxan diabetes mellitus failed to derange the trophoblast ultrastructure during the existence of placenta and produced no changes in the ultrastructure of the fetal vessels similar to the changes in the capillary ultrastructure of other organs and tissues in this pathology.     

Aldosterone production by isolated glomerulosa cells: modulation of sensitivity to angiotensin II and ACTH by extracellular potassium concentration.

The influence of extracellular potassium concentration on adrenal sensitivity to angiotensin II and ACTH was studied in isolated canine adrenal glomerulosa cells. When potassium was absent from the incubation medium, the aldosterone response to angiotensin II or ACTH was completely abolished. At physiologic angiotensin II concentrations (2.5 x 10(-11) M), aldosterone formation increased 4-fold when potassium concentration was increased from 2.5 to 5.0 mM, and rose 6-fold as potassium was increased from 2.5 to 7.5 mM. In the absence of angiotensin II, the same changes in potassium concentration increased aldosterone production only to 2-fold and 3.5-fold, respectively. The effect of potassium concentration upon the aldosterone response to ACTH was similar but less marked. The concentration and binding affinity of angiotensin II receptor sites in glomerulosa cells were not changed by increasing potassium concentrations from 0 to 7.5 mM. These observations demonstrate that the aldosterone response to the glomerulosa cell to angiotensin II is potassium-dependent within the physiological range for each of these stimuli. Such an interaction suggests that the in vivo effect of potassium upon aldosterone secretion includes a significant modulating action upon adrenal sensitivity to angiotensin II, as well as a direct action of potassium upon the adrenal glomerulosa cell.     

Comparative effect of angiotensin II, potassium, adrenocorticotropin, and cyclic adenosine 3',5'-monophosphate on cytosolic calcium in rat adrenal cells

The present study compares changes in cytosolic calcium and steroidogenesis when rat adrenal cells are stimulated with potassium (K+), angiotensin II (AII), ACTH, and (Bu)2cAMP (cAMP). The calcium-sensitive fluorescent dye, quin 2, was used to determine cytosolic calcium concentrations. K+ and AII both induced parallel increases in cytosolic calcium and aldosterone output. Removal of external calcium from the incubation media or addition of nifedipine inhibited the rise in cytosolic calcium in response to these two secretagogues. Inhibition of release of intracellularly-bound calcium by incubating the cells with 8-(N-N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride or dantrolene sodium reduced the rise in cytosolic calcium in response to these two secretagogues by 40-50%. In contrast, neither ACTH nor cAMP altered cytosolic calcium levels in the glomerulosa cells, even though quin 2-loaded cells showed a normal steroidogenic response to these agents. Thus, there was a dissociation between the cytosolic calcium response and steroidogenesis during cAMP stimulation of glomerulosa cells. Fasciculata cells incubated in the presence of increasing concentrations of cAMP, ACTH, K+, or AII failed to demonstrate an increase in cytosolic calcium, although the cells had a normal steroidogenic response to ACTH and cAMP. These results suggest that the responses of fasciculata and glomerulosa cells to secretagogues have different dependencies on calcium. The fasciculata cell has little calcium dependency while the glomerulosa cell has a variable dependency. In the glomerulosa cell, both AII and K+ induced similar responses in steroid output and cytosolic calcium, suggesting an important role for cytosolic calcium as a mediator of the steroidogenic effect of these secretagogues. Furthermore, part of the increase in cytosolic calcium induced by these agents is due to release of intracellularly bound calcium and part from increased calcium flux across the cell membrane. The absence of such dependency with cAMP suggests that an increase in intracellular calcium levels is not required for increased steroidogenesis in glomerulosa cells.