Production of aldosterone and its precursor steroids by the adrenal zona glomerulosa in dextran sulfate-treated rats

Heparin and heparinoids are known to produce selective aldosterone deficiency in man and experimental animals. To assess the nature of the hypoaldosteronism caused by heparin and heparinoids, we investigated the production of aldosterone and its precursor steroids in response to angiotensin II (AII), ACTH or potassium in adrenal zona glomerulosa cells from dextran sulfate-treated rats compared with that in the cells from vehicle-treated rats. Dextran sulfate-treated rats had a decrease in plasma aldosterone and a reduction in the width of the zona glomerulosa 4 weeks after the treatment (40 mg/day, intramuscularly). In these rats, PRA and plasma AII tended to be high, and plasma corticosterone was normal. Basal aldosterone production, when corrected to a uniform number of cells per group, was similar in cells from dextran sulfate- and vehicle-treated rats. The cells from dextran sulfate-treated rats had a less sensitive and lower response of aldosterone production to AII; an increase by 4 orders of magnitude in the threshold dose for AII and a decrease in the maximal AII-stimulated level. The maximal AII-stimulated levels, but not the basal levels, of pregnenolone, corticosterone and 18-hydroxycorticosterone production were low in the cells from dextran sulfate-treated rats. ACTH produced a similar stimulatory effect on aldosterone production in the cells from dextran sulfate- and vehicle-treated rats. The cells from dextran sulfate-treated rats had a less sensitive and lower response of aldosterone production to potassium; an increase by one order of magnitude in the threshold dose for potassium and a decrease in the maximum potassium-stimulated level, presumably because of the glomerulosa hyporesponsiveness to AII. These results suggest that long-term treatment with dextran sulfate in rats produces selective impairment of adrenal zona glomerulosa cells, involving the specific receptors and the aldosterone biosynthesis, to AII in addition to a reduction in the glomerulosa width.     

Effects of angiotensin II, ACTH, and KCl on the adrenal renin-angiotensin system in the rat

Angiotensin II, ACTH and potassium chloride were administered to rats for 6 days and the effects on adrenal renin-like activity and adrenal angiotensin II/III immunoreactivity were investigated. Rats infused with angiotensin II (140 pmol/min) either ip or sc showed increases in adrenal angiotensin II/III immunoreactivity (p less than 0.05) and plasma aldosterone concentration (p less than 0.05), but no change in adrenal renin-like activity. Captopril treatment of angiotensin II-infused rats caused a slight decrease in angiotensin II/III immunoreactivity which did not reach statistical significance. In contrast, rats treated with ACTH (Cortrosyn-Z, 3 IU/day, sc) showed an increase in adrenal renin-like activity (p less than 0.01), but no significant change in adrenal angiotensin II/III immunoreactivity. Rats treated with KCl in drinking water showed increases (p less than 0.05) in adrenal renin-like activity, adrenal angiotensin II/III immunoreactivity, and plasma aldosterone. These results suggest that angiotensin II, ACTH and potassium, three major regulators of aldosterone secretion by the adrenal gland, have different effects on the adrenal renin-angiotensin system when administered in vivo.     

Aldosterone production by isolated adrenal glomerulosa cells: stimulation by physiological concentrations of angiotensin II.

The production of aldosterone by isolated canine zona glomerulosa cells was measured after the incubation of cell suspensions with angiotensin II and ACTH, and during changes in extracellular potassium concentration. Adrenal cell suspensions were prepared by collagenase digestion and physical dispersion of the capsular layer of the dog adrenal cortex, and aldosterone production was determined by direct radioimmunoassay of cell incubation media. The isolated dog adrenal cells were highly responsive to angiotensin II, with aldosterone production significantly stimulated by concentrations of the octapeptide as low as 10(-11)M. Thus, the steroidogenic response of zona glomerulosa cells was consistently observed at peptide concentrations within the physiological range of angiotensin II in dog plasma, i.e., 2.0-5.0 X 5.0 X 10(-11)M. The maximum aldosterone response of 3-8 times the basal level of steroid production was induced by 3 X 10(-10)M angiotensin II, and a decrease in aldosterone production occurred at peptide concentrations above 10(-9)M. The aldosterone response of isolated adrenal cells to ACTH was consistently less sensitive than their response to angiotensin II, by a factor of 10-20 fold. Aldosterone production was significantly increased by 10(-10)M ACTH, and reached a maximum at 10(-8)M ACTH. By contrast with angiotensin II, ACTH usually evoked a higher maximal level of aldosterone production, and did not produce a decline in steroidogenesis at peptide concentrations above the level which caused maximum stimulation of aldosterone formation. Changes in the potassium concentration of cell incubation media were also accompanied by marked effects upon aldosterone synthesis which was abolished in the absence of potassium and became detectable in the presence of 0.5 mM K+. After remaining constant between 2.5 and 4.0 mM K+, aldosterone production rose sharply above 4.5 mM K+ and reached a maximum at 8 mM K+. These observations provide direct evidence that aldosterone production by zona glomerulosa cells is influenced by changes in angiotensin II levels within the normal plasma range.     

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.     

Effects of prolonged cyclosporine-A treatment on the morphology and function of rat adrenal cortex

The effects of prolonged (30 day) treatment with daily therapeutical doses of cyclosporine A (CSA) (20 mg/kg) on the function and morphology of adrenal cortex were studied in adult male rats. CSA-treated animals developed a notable hypertension, along with a striking rise in PRA, which was not coupled with significant changes in the plasma concentrations of aldosterone and corticosterone (hyperreninemic hypoaldosteronism). Morphometry showed that zona glomerulosa (ZG) and zona fasciculata, and their parenchymal cells were atrophic. Isolated capsular (ZG) and inner (zona fasciculata/reticularis) cells displayed reduced basal and stimulated secretory responses. However, while the response of ZG cells to angiotensin II was almost completely suppressed (96%), basal steroid secretion of isolated cells, as well as the aldosterone and corticosterone response of ZG cells to potassium and ACTH, and corticosterone production of inner cells in response to ACTH were decreased by only about 30-40%. The hypothesis is advanced that CSA exerts a dual effect on rat adrenal cortex: 1) a general inhibitory effect on the growth and steroidogenic capacity of adrenocortical cells, which manifests itself only after very prolonged treatment and may be caused by an impairment of protein synthesis; and 2) an acute effect involving the specific blockade of the angiotensin-II-induced stimulation of the secretory activity of ZG cells.     

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.     

Prolonged infusions of Ile5-angiotensin-II in sodium replete and deplete man: effects on aldosterone, ACTH, cortisol, blood pressure, and electrolyte balance.

Angiotensin II (Ile5) was infused for 72 h into 4 sodium replete (3 ng/kg/min) and 8 sodium deplete (3 or 6 ng/kg/min) healthy young men after appropriate control periods, and the effects on aldosterone secretion, plasma cortisol, ACTH, renin activity, plasma and urinary electrolytes, and blood pressure were assessed. Sustained contrived elevation of plasma angiotensin II levels in sodium replete subjects to the range of moderate sodium depletion led to a sustained increase in plasma and urinary aldosterone levels, which further and significantly increased between the 1st and 2nd days of angiotensin II infusion, when gross sodium retention during infusion was prevented. This additional increase may be explained as the expression of a "trophic" effect of angiotension II on the zona glomerulosa. In the sodium deplete state, the absolute increment of aldosterone secretion for a given elevation of angiotensin II levels diring infusion was larger than in sodium replete subjects. This confirms the conclusions from previous short-term angiotensin II infusion experiments that sodium deficiency sensitizes the zona glomerulosa against angiotensin II. The "trophic" effect of angiotensin II on the adrenal gland seems to be one mechanism by which the sensitization is brought about, but insufficient for its full explanation. Since plasma ACTH and cortisol, plasma sodium and potassium concentrations, and potassium blance did not change significantly across sodium depletion or angiotensin II infusion, the mechanism of sensitization awaits its full elucidation. The effect of angiotensin II on blood pressure was blunted by soidum depletion. The opposite shifts in sensitivity against angiotensin II of the zona glomerulosa and of resistance blood vessels with changes in the sodium state seem to be an effective and important means in the regulation of body sodium.     

Effect of angiotensin II on aldosterone and its precursor steroid production in adrenal zona glomerulosa cells from heparin-treated rats

To assess the nature of the heparin-induced aldosterone deficiency, we investigated the stimulatory effect of angiotensin II (AII) on aldosterone and its precursor steroids in adrenal zona glomerulosa cells from heparin-treated rats compared with those in the cells from vehicle-treated rats. Heparin-treated rats had low plasma aldosterone levels, high plasma renin activity and plasma AII levels, and normal plasma corticosterone level 6 weeks after the treatment (1500 IU/kg, twice daily). Basal aldosterone production, when corrected to a uniform number of cells per group, was similar in the cells from heparin- and vehicle-treated rats. The cells from heparin-treated rats had a less sensitive and lower response of aldosterone production to AII; an increase by 4 orders of magnitude in the threshold dose for AII and a decrease in the maximum AII-stimulated level. The maximum AII-stimulated levels, but not the basal levels, of pregnenolone, corticosterone and 18-OHB production were low in the cells from heparin-treated rats. ACTH caused a similar stimulatory effect on aldosterone production in the cells from heparin- and vehicle-treated rats. The cells from heparin-treated rats had a less sensitive and lower response of aldosterone production to potassium; an increase by one order of magnitude in the threshold dose for potassium and a decrease in the maximum potassium-stimulated level, presumably because of the glomerulosa hyporesponsiveness to AII. These results suggest that our heparin-treated rats have selective impairment of adrenal zona glomerulosa cells, involving the specific receptors and the aldosterone biosynthesis, to AII.     

Primary Aldosteronism: Effects of Inhibition of ACTH and Potassium Administration on Plasma Aldosterone Concentration

The relative roles of ACTH, angiotensin and potassium in influencing aldosterone secretion in primary aldosteronism were assessed by direct or indirect means. In untreated patients with primary aldosteronism caused either by adrenal adenoma or hyperplasia plasma aldosterone and cortisol concentrations fluctuated in unison and dexamethasone reduced both hormones markedly. Only when renin-angiotens in system was greatly activated and plasma potassium normalized by medical treatment was dexamethasone less successful in lowering plasma aldosterone concentration. Potassium infusion of 10, 20 and 30 mEq/hr in patients with adenoma failed to elicit any increase in plasma aldosterone concentration despite significant increases in plasma potassium levels. These results suggest that patients with primary aldosteronism due to adrenal adenoma are relatively more sensitive to small changes in plasma ACTH level than those in plasma angiotensin or potassium levels. In recumbent patients with adrenal hyperplasia ACTH also modulates plasma aldosterone concentration.     

Primary Aldosteronism: Effects of Inhibition of ACTH and Potassium Administration on Plasma Aldosterone Concentration

The relative roles of ACTH, angiotensin and potassium in influencing aldosterone secretion in primary aldosteronism were assessed by direct or indirect means. In untreated patients with primary aldosteronism caused either by adrenal adenoma or hyperplasia plasma aldosterone and cortisol concentrations fluctuated in unison and dexamethasone reduced both hormones markedly. Only when renin-angiotensin system was greatly activated and plasma potassium normalized by medical treatment was dexamethasone less successful in lowering plasma aldosterone concentration. Potassium infusion of 10,20 and 30 mEq/hr in patients with adenoma failed to elicit any increase in plasma aldosterone concentration despite significant increases in plasma potassium levels. These results suggest that patients with primary aldosteronism due to adrenal adenoma are relatively more sensitive to small changes in plasma ACTH level than those in plasma angiotensin or potassium levels. In recumbent patients with adrenal hyperplasia ACTH also modulates plasma aldosterone concentration.     

Modulation of aldosterone secretion in frusemide-induced hypokalaemia

To study the effect of hypokalaemia in the regulation of aldosterone secretion, repeated injections of frusemide (3 mg/kg) plus saline with or without simultaneous infusion of potassium chloride (1 mEq/kg/h) were performed in 24 conscious female rabbits for 7 h. Without potassium supplementation, the plasma renin activity (PRA) remained elevated throughout the study, while an initial increase (1 h to 3 h) in plasma aldosterone (PA) gradually returned to normal with reduction of the serum potassium. In rabbits on potassium supplements to prevent the development of hypokalaemia, both PRA and PA remained elevated. The incremental aldosterone response to administration of potassium chloride, angiotensin II or ACTH, was considerably smaller in potassium-depleted rabbits than in potassium-repleted rabbits. These results suggest that serum potassium modulates the effects of angiotensin II or ACTH on aldosterone secretion, and that a certain level of potassium is necessary to maintain the aldosterone secretory capacity of the adrenal gland.     

Regulation of the adrenal renin angiotensin system in cultured bovine zona glomerulosa cells: effect of catecholamines.

The renin-angiotensin system consists of two main enzymes, renin and angiotensin-converting enzyme, which lead to the formation of angiotensin-II. Angiotensin-II is a potent vasoconstrictor and stimulates the production of aldosterone. In this study we examined the effect of ACTH, potassium, (Bu)2cAMP (dbcAMP), and catecholamines on the adrenal renin-angiotensin system. To study the production of renin and aldosterone in vitro, we developed a monolayer culture of bovine zona glomerulosa cells in serum-free medium. Collagenase-dispersed zona glomerulosa cells were incubated in Pasadena Foundation for Medical Research-4 medium containing 10% fetal calf serum for 72 h, and the medium was replaced with serum-free medium for the next 24 h of the experimental period. The cells during this 24 h were exposed to various doses of ACTH, potassium, dbcAMP, and sympathomimetic agents. ACTH and dbcAMP stimulated aldosterone secretion, and this secretion was associated with an increase in renin activity in cells and medium. Aldosterone was also stimulated by high doses of potassium, and potassium had a stimulatory effect on the secretion of renin in medium. Catecholamines had a weak stimulating effect on aldosterone secretion and were potent stimulators of adrenal renin activity in cells and medium. Dopamine had no significant effect on basal aldosterone secretion or renin activity in cells and medium. In conclusion, these data indicate that adrenal renin is synthesized in bovine zona glomerulosa cells in vitro, and that ACTH and dbcAMP stimulate adrenal renin and aldosterone production. Furthermore, adrenal renin, like renal renin, may be under the control of the sympathetic nervous system.     

Mechanisms of inhibition of aldosterone secretion by adrenocorticotropin

The mechanisms by which prolonged administration of ACTH causes a decrease in aldosterone secretion were studied in the rat. After 6 days of treatment with ACTH (2 U/day), blood corticosterone was elevated and plasma aldosterone was decreased in rats maintained on either a normal or low sodium diet. PRA was also decreased, probably secondary to increased sodium and/or fluid retention. In collagenase-dispersed glomerulosa cells from adrenals of ACTH-treated rats, angiotensin II receptors were markedly decreased, as were the in vitro aldosterone responses to angiotensin II, ACTH, 8-bromo-cAMP, and potassium. However, the production of deoxycorticosterone and precursor steroids was increased, indicating the presence of a block in the late aldosterone biosynthetic pathway. Measurement of the activity of biosynthetic enzymes of the steroidogenic pathway in isolated mitochondria revealed an 80% increase in side-chain cleavage enzyme in both glomerulosa and fasciculata mitochondria from ACTH-treated rats. Although ACTH injection also increased 11-hydroxylase activity in the fasciculata zone, this enzyme was reduced by 50% in capsular mitochondria. The 18-hydroxylase activity in adrenal capsular mitochondria was markedly decreased by ACTH treatment in both normal and sodium-restricted animals. The importance of ACTH-induced steroidogenesis in the development of altered glomerulosa cell function was indicated by the ability of aminoglutethimide to prevent the inhibitory effects of ACTH on angiotensin II receptors and PRA. It is likely that the observed inhibition of the renin-angiotensin system is responsible for the decrease in angiotensin II receptors and 18-hydroxylase, since both are highly dependent on the trophic effect of angiotensin II. The specific lesions produced in adrenal glomerulosa cells by long term ACTH treatment include decreased levels of angiotensin II receptors, 11-hydroxylase, and 18-hydroxylase. These changes are secondary to the suppression of renin-angiotensin activity and are responsible for the impaired aldosterone secretion that results from prolonged treatment with ACTH. (Endocrinology 108: 522, 1981)     

Suppression of aldosterone biosynthesis by treatment of rats with adrenocorticotropin: comparison with glucocorticoid effects.

The treatment of rats with a high dose of ACTH resulted within 4 days in a marked suppression of aldosterone and deoxycorticosterone outputs by capsular adrenal tissue ("zona glomerulosa") incubated with and without serotonin and in decreased conversions of tritiated corticosterone and deoxycorticosterone to aldosterone and 18-hydroxycorticosterone, but in strikingly increased capsular adrenal conversions of tritiated deoxycorticosterone to corticosterone and 18-hydroxy deoxycorticosterone. ACTH also suppressed aldosterone biosynthesis in rats kept on a sodium-deficient diet. Corticosterone or dexamethasone, when added to the drinking fluid for 2 weeks, induced only small decreases in aldosterone biosynthesis from endogenous or exogenous precursors. Moreover, they significantly decreased the capsular adrenal conversion of added deoxycorticosterone to corticosterone and 18-hydroxydeoxycorticosterone. These results indicate that during prolonged ACTH treatment, the zona glomerulosa cell may be converted to a functional zona fasciculata type of cell. High levels of circulating mineralocorticoids and glucocorticoids seem to be minor contributory factors in the long term suppression of aldosterone biosynthesis by ACTH.     

Role of the renin-angiotensin system in the regulation of late steps in aldosterone biosynthesis by sodium intake of potassium-deficient rats

The role of the renin-angiotensin system in the adaptation of late steps in aldosterone biosynthesis to sodium intake was studied in potassium-deficient rats. Capsular portions of adrenal glands were incubated with [3H]corticosterone and conversion to aldosterone and 18-hydroxycorticosterone was measured by double isotope dilution and multiple paper chromatography. Sodium loading of sodium- and potassium-depleted rats resulted in a rapid and extensive fall in PRA but only in a delayed and gradual suppression of aldosterone biosynthesis. Treatment with the converting enzyme inhibitor, captopril, did not affect aldosterone biosynthesis in rats with established sodium and potassium deficiency, but blocked the stimulation of the conversion of corticosterone to aldosterone and 18-hydroxycorticosterone by sodium restriction of potassium-depleted rats. Infusion of a high dose of angiotensin II into potassium-deficient rats stimulated aldosterone biosynthesis depending upon the concurrent sodium intake. Accordingly, the renin-angiotensin system plays an important but limited role in the control of late steps of aldosterone biosynthesis by sodium intake. Angiotensin II seems to be essential for the induction but not for the maintenance of a high activity of the enzyme(s) involved in the conversion of corticosterone to aldosterone during combined sodium and potassium restriction. The sensitivity of the zona glomerulosa to the long term stimulatory action of angiotensin II varies with the sodium intake and appears to be regulated by the plasma potassium concentration and unknown other mediators.     

Effects of prolonged infusions of potassium chloride, adrenocorticotrophin or angiotensin II upon serum aldosterone concentration and the conversion of corticosterone to aldosterone in rats.

The temporal relation between alterations in serum aldosterone and in the conversion of labelled corticosterone to aldosterone by incubated adrenal tissue was studied in conscious rats receiving long-term infusions of KCl, ACTH or angiotensin II. When potassium-deficient rats were given KCl, a marked increase in serum aldosterone was observed only after 12 h, i.e. at a time when the conversion of corticosterone to aldosterone had become normal. After 24 h of ACTH infusion into sodium- and potassium-replete rats the serum aldosterone was markedly elevated, whereas the conversion of corticosterone to aldosterone was significantly decreased. After 48 h of continued ACTH infusion the serum aldosterone returned to normal and there was a further decrease in the conversion rate. A 24-h angiotensin II infusion into sodium- and potassium-replete rats induced significant increases in both the serum aldosterone and the conversion. After 48 h of continued angiotensin infusion the serum aldosterone returned to normal while the conversion and the blood pressure remained elevated. These results indicate that the activity of the enzymes involved in the final steps of aldosterone biosynthesis may become rate-limiting for the secretion of aldosterone during potassium deficiency and during prolonged ACTH treatment. On the other hand, the observed transiency of aldosterone stimulation by exogenous angiotensin II was not due to a suppression of the final steps of aldosterone biosynthesis and remains unexplained.     

Selective inhibition by des-1-Asp-8-lle-angiotensin ii of the steroidogenic response to restricted sodium intake in the rat.

Angiotensin III (des-1-Asp-angiotensin II) is a potent steriodogenic agent in many species. The effects of the heptapeptide in the adrenal zona glomerulosa are resistant to blockade by C-terminally substituted analogues of angiotensin II (1-Sar-8-Ile- or 1-Sar-8-Ala-octapeptides). For this reason, the effects of 7-Ile-angiotensin III, a C-terminally substituted analogue of the heptapeptide, and 1-Sar-8-Ile-angiotensin II on aldosterone biosynthesis in rabbit adrenal cortical cell suspensions and on urinary aldosterone excretion in sodium-deprived rats were studied. In the vitro studies, 7-Ile-angiotensin III was a better antagonist of angiotensin II- or angiotensin III-induced steroidogenesis than was 1-Sar-8-Ile-angiotensin II. In the rats, subcutaneously administered 1-Sar-8-Ile-angiotensin II (0.9 mumoles/kg) produced prolonged blockade of the pressor responses to exogenous angiotensin II. 70Ile-angiotensin III (0.9 mumoles/kg) had no effect on resting blood pressure or on blood pressure responses to angiotensin II infusions. At the doses studied, however, 7-Ile-angiotensin III caused a marked decrease (50%) in aldosterone excretion in sodium-deprived rats, but 1-Sar-8-Ile-angiotensin II had no effect on aldosterone excretion. In the sodium-deprived rats, the administration of 7-Ile-angiotensin Ile was not associated with an acute increase in plasma renin activity, but treatment with 1-Sar-8-Ile-angiotensin II resulted in a sixfold increase in plasma renin activity, but otensin III was not associated with an acute increase in plasma renin activity, but treatment with 1-Sar-8-Ile-angiotensin II resulted in a sixfold increase in plasma renin activity. These results are consistent with a role for angiotensin III in the control of aldosterone biosynthesis.     

Zonal distribution and regulation of adrenal renin in a transgenic model of hypertension in the rat.

The hypertensive transgenic rat [TGR (mRen-2)27] is a genetic model of hypertension in which transfection of the Ren-2 mouse renin gene into rats results in severe hypertension. These transgenic rats express a high level of renin in the adrenal gland, and the hypertension is ameliorated by treatment with angiotensin-converting enzyme inhibitors. In this study we investigated the distribution of adrenal renin in the TGR rat and examined the regulation of adrenal renin in a monolayer culture of adrenal cells. High concentrations of active renin and prorenin were found in the adrenal capsular (glomerulosa) and decapsular (fasciculata-medullary) portions of the TGR adrenal. This is in contrast with the Sprague-Dawley (S-D) rat, in which adrenal renin is found mostly in the active form and located primarily in the glomerulosa cells. The zonal distribution of aldosterone was also different in the TGR, with substantial amounts of aldosterone in the zona fasciculata as well as in the glomerulosa, while in the S-D rat, aldosterone is limited to the zona glomerulosa. In the primary monolayer culture of glomerulosa cells, TGR cells had significantly higher levels of active renin and prorenin and showed an increased response to ACTH and high potassium in the medium. Renin activity in the medium was predominantly in the form of prorenin and significantly higher than that in the S-D rat. Cultured fasciculata cells from TGR also produce renin that is stimulated by ACTH, but not by a high potassium concentration. Renin activity in the adrenal homogenate, medium, and plasma from TGR rats was completely inhibited by the renin inhibitor (CP 71362; 1 microM), but only slightly inhibited (12.3 +/- 3%) by a monoclonal antibody that inhibits renin activity from S-D rat tissues by 79.2 +/- 2.5%, suggesting that renin in the plasma and adrenal glands from TGR appears to derive primarily from mouse renin. In conclusion, the TGR (mRen-2)27 rats have higher than normal levels of adrenal renin, and the cultured cells show an exaggerated renin response to ACTH and potassium. The distribution of the renin enzyme in the adrenal zones of the TGR is similar to the distribution of mouse adrenal renin.     

Pomc knockout mice have secondary hyperaldosteronism despite an absence of adrenocorticotropin

Aldosterone production is controlled by angiotensin II, potassium, and ACTH. Mice lacking Pomc and its pituitary product ACTH have been reported to have absent or low aldosterone levels, suggesting that ACTH is required for normal aldosterone production. However, this is at odds with the clinical finding that human aldosterone deficiency is not a component of secondary adrenal insufficiency. To resolve this, we measured plasma and urine electrolytes, together with plasma aldosterone and renin activity, in Pomc(-/-) mice. We found that these mice have secondary hyperaldosteronism (elevated aldosterone without suppression of renin activity), indicating that ACTH is not required for aldosterone production or release in vivo. Exogenous ACTH stimulates a further increase in aldosterone in Pomc(-/-) mice, whereas angiotensin II has no effect, and the combination of angiotensin II and ACTH is no more potent than ACTH alone. These data suggest that aldosterone production and release in vivo do not require the action of ACTH during development or postnatal life and that secondary hyperaldosteronism in Pomc(-/-) mice is a consequence of glucocorticoid deficiency.     

Zona glomerulosa morphology and function in streptozotocin-induced diabetic rats

Streptozotocin-induced diabetic rats showed a significant lowering in both PRA (-31%) and basal plasma aldosterone concentration (-59%), coupled with a notable atrophy of the zona glomerulosa (-30%) and its parenchymal cells (-36%). Kalaemia and the blood level of ACTH were not affected. Insulin infusion reversed all the streptozotocin-evoked effects. Analogous, though less conspicuous, changes were induced by experimental diabetes also in rats whose hypothalamo-hypophyseal-adrenal axis and renin-angiotensin system had been pharmacologically interrupted by the simultaneous administration of dexamethasone-captopril and maintenance doses of ACTH-angiotensin II: the drops in the basal plasma aldosterone concentration and in the volume of zona glomerulosa and its cells ranged from -20% to -22%. In these animals, experimental diabetes significantly depressed the aldosterone response to the acute stimulation with angiotensin II (-55%), potassium (-50%), and ACTH (-43%). These findings indicate that the well known impairment of renin release may only partially account for the antiadrenoglomerulotrophic effect of experimental diabetes in rats. The hypothesis is advanced that the chronic lack of insulin may directly depress both the growth of the zona glomerulosa and the newly synthesis of some enzymes of aldosterone synthesis.