Steroid synthesis in the adrenal gland of the sea snake Hydrophis cyanocinctus: The metabolism of exogenous precursors

Sea snake (Hydrophis cyanocinctus) adrenal glands (whole homogenates, preincubated minces, or mitochondrial preparations) were incubated in vitro with exogenous radioactive precursors. Hydrophis adrenal tissue was capable of synthesizing 17-deoxycorticosteroids from exogenous cholesterol, pregnenolone, progesterone, and DOC, but not from sodium [¹⁴C]-acetate. Products identified after incubation were pregnenolone, progesterone, 11β-hydroxyprogesterone, DOC, corticosterone, 18-hydroxycorticosterone, and aldosterone. The major product was corticosterone with lesser quantities also of 18-hydroxycorticosterone and aldosterone. In the case of the mitochondrial preparation 11β-hydroxyprogesterone predominated. No evidence for the biosynthesis of cortisol from cholesterol was found. Two types of kinetic incubation were employed: One sampled the incubation medium alone, while the other sampled both medium plus tissue. It was concluded that sampling the medium only did not allow the identification of the biosynthetic pathways operating in vitro. However, from sampling both the medium and the tissue it was concluded that both the C21-C11 and C11-C21 sequences of hydroxylation operated in the conversion of progesterone to corticosterone. The data contrast with those obtained from previous studies on cobra adrenal tissue, particularly with regard to the ability of sea snake adrenals in vitro to 18-oxygenate exogenous precursors.     

Adaptation to fresh water in the sea snake Hydrophis cyanocinctus: Tissue electrolytes and peripheral corticosteroids

Groups of mature sea snakes, Hydrophis cyanocinctus, were transferred from seawater to tanks of running fresh water and sampled at 10, 16, 21, 27, 31, 35, and 51 days after transfer. The following were measured as parameters of adaptation to fresh water and compared with control (seawater maintained) animals: rate of weight loss; muscle water and ion content; blood hematocrit; plasma osmolarity; plasma Na⁺, K⁺, Cl^?, and urea concentrations. Peripheral levels of corticosterone and aldosterone were measured using competitive protein binding assay and radioimmunoassay, respectively. Adrenal in vitro 18-oxygenase activity was determined radiometrically using [³H]corticosterone. The rate of weight loss was lower in snakes in fresh water, but hematocrit and tissue water composition were unaltered. Plasma ion concentrations and total osmolarity fell significantly within 10 days and stabilized after approximately 16 days. Only after 51 days did muscle ionic composition or plasma $\text{Na}{}^{\mathrm{+}}\text{K}{}^{\mathrm{+}}$ alter. Urea was below detectable levels in all animals. Peripheral aldosterone concentrations remained at 1 to 4 μg/100 ml plasma whereas mean corticosterone titers fell significantly from 8 to 3 μg/100 ml. Adrenal in vitro 18-oxygenase activity was, however, significantly increased after 51 days of freshwater treatment. It was concluded that H. cyanocinctus is an osmoconforming euryhaline reptile, and possible roles for the adrenal in hydromineral balance are discussed.     

In vitro corticosteroidogenesis by the adrenal gland of the chicken (Gallus domesticus)

[4-¹⁴C]Pregnenolone, [4-¹⁴C]progesterone, and [4-¹⁴C]11-deoxycorticosterone were indubated with chicken adrenal tissue slices, whole homogenates, and subcellular fractions, with and without the addition of ACTH to the incubation medium. Progesterone, 11-deoxycorticosterone, corticosterone, 11β-hydroxyprogesterone, and aldosterone were identified as metabolites of these radioactive precursors. The rate of conversion of pregnenolone to progesterone by the slices and progesterone to corticosterone by the mitochondrial fraction significantly increased by the addition of ACTH to the medium. The activity of Δ⁵-3β-hydroxysteroid dehydrogenase associated with Δ⁵-Δ⁴ isomerase upon pregnenolone and the activity of 21-hydroxylase upon progesterone were concentrated in the microsomal fraction, while the activity of 11β-hydroxylase upon 11-deoxycorticosterone was in the mitochondrial fraction. No 17α-hydroxylase activity was observed.The main pathway for steroidogenesis in the chicken adrenal gland is proposed to be: pregnenolone → progesterone → 11-deoxycorticosterone → corticosterone.     

Seasonal variation in adrenal 11beta-hydroxysteroid dehydrogenase activity in the meadow vole (Microtus pennsylvanicus).

[4-¹⁴C]Progesterone is converted to corticosterone by adrenal homogenates of Microtus pennsylvanicus. The 11-keto derivative, 11-dehydrocorticosterone, is a secondary conversion product formed by the action of an adrenal 11β-hydroxysteroid (11β-OHD) dehydrogenase on corticosterone. There is a marked seasonal variation in the 11β-OHD enzyme with peak activity in late fall-winter and very low activity in early spring and summer. Adrenal 11β-OHD enzyme activity is greatest during the period when adrenal responsiveness is low and the voles are reproductively inactive.     

Sex differences in steroidogenesis by adrenal homogenates of adult possum (Trichosurus vulpecula) attributable to the steroids formed by the adrenocortical special zone of the female

A marked sex difference was found in the nature of steroid conversion products formed from [¹⁴C]progesterone by whole adrenal homogenates of adult possums. The major conversion products from adrenals of males were: cortisol in yields of 46 ± 2% and corticosterone, 25 ± 2% (mean ± SEM, n = 35). The total 5β-reduced products were <10%. With glands from females 5β-reduced products comprised >80% of the yield, the predominant steroids being 5β-pregnane-3α,17α-diol-20-one, 25 ± 4% and 5β-pregnane-3α-o1-20-one, 21 ± 3% (mean ± SEM, n = 39). The yields of cortisol was <8%. No significant difference was found in the yields of products from animals used on the day of capture from the wild, or taken from the animal house 1–12 months after capture. Studies were carried out on the separated adrenocortical special zone and cortex proper of females. Homogenized cortex proper incubated with [¹⁴C]progesterone formed mainly: cortisol, 28 ± 2%; corticosterone, 18 ± 3%; and 11β-hydroxyprogesterone, 24 ± 4% (mean ± SEM). From the same substrate the conversion products by the homogenized special zone were 5β-reduced pregnane derivates in yields >70% and reduced 5α- and 5β-androstan derivates, <15%. The products of major yield were: 5β-pregnan-3α-o1-20-one, 5β-pregnane-3α,17α-diol-20-one, and 5β-pregnane-3α,17α,20α-triol. Similarly from [17α-¹⁴C]hydroxyprogesterone and [11-¹⁴C]deoxycortisol substrates the conversion products by the special zone were mainly 5β-reduced pregnane derivates, the C19 steroids being <10%. Dissected medullary tissue had no steroidogenic activity. The addition of medullary tissue to cortex proper had no effect on the synthetic activity of the cortex. With mixtures of cortex proper and special zone the conversion products were similar to those obtained by whole adrenal homogenates. It is concluded that the dissimilarity in the adrenal steroid formation was due to the activity of the 5β-reductase, which prevailed in the female adrenal and was very low in the male adrenal. It was found that the location of the reducing enzymes was specific to the unique adrenocortical special zone which is present only in the female possum.     

11 beta-Hydroxysteroid dehydrogenase activity in the renal target cells of aldosterone

Aldosterone selectivity in mineralocorticoid target tissues has been suggested to be due to 11 beta-hydroxysteroid dehydrogenase (11-OHSD), which, by inactivating the endogenous glucocorticoids cortisol and corticosterone (CS), would allow aldosterone to bind to the mineralocorticoid receptor that has equal affinity for aldosterone and natural glucocorticoids. However, a recent immunohistochemical study failed to colocalize 11-OHSD and mineralocorticoid receptors in the kidney. The goal of this study was to determine 1) whether metabolism of CS occurs in the renal target cells of aldosterone, i.e. in cortical collecting duct cells, and 2) if it does so, whether this activity is sufficient to reduce intracellular CS levels to allow binding of aldosterone to the mineralocorticoid receptor. Cortical collecting duct cells were isolated by solid phase immunoadsorption, with a cell purity of approximately 98%. Metabolism of CS was studied in both freshly isolated cells and primary cultures grown as monolayers on permeable supports. Freshly isolated cells rapidly converted CS to 11-dehydro-CS, which was the only major metabolite detected. In intact collecting duct cells 11-OHSD had an apparent Km for CS of approximately 60 nM, a value more than 100-fold lower than the Km of 11-OHSD in the rat liver, and a maximum velocity of approximately 1.7 x 10(-14) mol/min.1000 cells. In cultured cells, when [3H]CS was applied to one side of the monolayer, almost all radioactivity on the opposite side was 11-dehydro-CS. The cells were able to almost completely metabolize CS passing through them for up to a concentration of 2.5 x 10(-7) M. Carbenoxolone, an inhibitor of 11-OHSD, reduced CS degradation by 88%. Neither freshly isolated nor cultured collecting duct cells converted [3H]11-dehydro-CS back to CS in a significant amount (less than 1%). These data provide functional evidence for 11-OHSD activity in renal aldosterone target cells and indicate that this enzyme might be a collecting duct-specific isoform of 11-OHSD which can sufficiently reduce intracellular CS concentrations to contribute to the apparent mineralocorticoid selectivity of the collecting duct.     

In vitro steroidogenesis by the nonzoned adrenocortical tissue of the skink, Tiliqua rugosa.

Steroid formation by adrenocortical tissue from the shink, Tiliqua rugosa, has been studied using established in vitro techniques. Both in conventional incubations, with timed sampling, and in incubations with dialysis, aldosterone, and corticosterone were major products. From endogenous precursors, and from [¹⁴C]acetate, yields of the two products were of the same order, whereas from [³H]pregnenolone maximal yields of corticosterone were at least tenfold greater than aldosterone. Maximal rates of steroid formation from the radioactive precursors occurred within the first few minutes of incubation, but maximal rates of steroid formation from endogenous precursors occurred significantly later, between 1–2 hr.In incubations with dialysis [¹⁴C]aldosterone was significantly less dialysable than [³H]aldosterone under all conditions, whereas [¹⁴C] and [³H]corticosterone were homogeneous. In contrast, neither aldosterone nor corticosterone formed from endogenous precursors were bound under control conditions, although binding was increased following dexamethasone pretreatment, and decreased following stimulation with Tiliqua pituitary extract (but not Synacthen), with concomitant changes in yields and specific activities.Inter alia the results suggest that products formed from [¹⁴C]acetate and from [³H]pregnenolone may be maintained in separate pools within the tissue, and this accounts for their different metabolic fates. The bound pool, penetrated only by [³H]acetate, yields more aldosterone than the free, and may be termed a “biosynthetic pool.” In addition there exists a “secretory reserve pool.” This is suggested by the difference between rates of steroid secretion from endogenous and added precursors, and also from the changes in dialysibility seen in steroids formed from endogenous precursors under different conditions of stimulation.In both the compartmental arrangement of steroids, and the production of large yields of aldosterone the adrenocortical tissue of Tiliqua shows similarities to the zona glomerulosa, but not the inner zones of the rat adrenal cortex.     

In vitro study of frog (Rana ridibunda Pallas) interrenal function by use of a simplified perifusion system III. Influence of previous hypophysectomy or dexamethasone treatment of donors upon corticosterone and aldosterone production

Effects of long-term hypophysectomy and dexamethasone treatment on interrenal function of Rana ridibunda have been studied in vitro by use of a perifusion system technique. Hypophysectomy significantly reduced secretory activity of interrenal tissue (nearly 60% reduction for both corticosterone and aldosterone biosynthesis) but did not affect interrenal responsiveness to crude homologous pituitary extract and did not modify the ratio aldosterone/corticosterone as well. Daily injections of 1 mg dexamethasone during 20 days diminished both corticosterone and aldosterone productions by interrenal tissue to about 40% of those of glands from normal animals. Dexamethasone treatment did not alter interrenal responsiveness to crude homologous pituitary extract. In addition, daily injections of 0.6% NaCl solution for 18 days (0.25 ml/animal) resulted in a specific decrease in aldosterone secretion. Aldosterone/corticosterone secretion ratios were 2.1 in normal frogs, 2.3 in hypophysectomized frogs, 2.2 in sham-hypophysectomized frogs, and 1.9 in dexamethasone-treated frogs. This ratio fell to 1.3 in saline-treated frogs. These in vitro results are consistent with previous in vivo data on anuran pituitary-interrenal relationships which had demonstrated partial independence of interrenal function from pituitary control. They also provide evidence that alteration of electrolyte balance specifically modifies aldosterone production without significant change in corticosterone biosynthesis.     

Circadian variation in activity of the duck (Anas platyrhynchos) adrenal gland

Duck adrenal glands were studied with respect to circadian activity by incubating with progesterone-4-¹⁴C at 2-hour intervals for 24 hr. The production of deoxycorticosterone, corticosterone, and aldosterone was studied in quadruplicate incubations. Results show that peak production of corticosterone and aldosterone occurred at early morning at 06.00–08.00 hr and again in the late afternoon, 16.00–20.00 hr. Production of these two hormones was at minimum at midday and midnight. Unlike the mammalian species studied which exhibit a 24-hr cycle change in adrenal activity, the duck shows a characteristic 12-hr cycle. This pattern of circadian activity of the adrenal reflects to some degree the physiology of the animals in that the peaks of adrenal activity coincide with times of maximal body activity.     

The in vitro biosynthesis of steroids from pregnenolone and cholesterol and the effects of bovine ACTH on corticoid production by adrenal glands of embryonic chicks.

Groups of 10 pairs of adrenal glands obtained from embryonic chicks which had been incubated for 15 days were maintained in vitro for up to $\text{3}\text{1}\text{2}$ hr in the presence of [³H]-pregnenolone, [³H]cholesterol, or [H]pregnenolone + ACTH. Steroids, both those synthesised and retained by the glands and those secreted into the culture medium, were separated by thin-layer chromatography and their concentrations were determined by liquid scintillation counting. The steroids assayed were: progesterone, 11-deoxycorticosterone, 17α-OH-progesterone, corticosterone, cortisol, cortisone, and aldosterone. Pregnenolone was predominantly utilized in the synthesis of 17α-OH-progesterone. Insufficient labeled cortisone and cortisol were produced to account for the 17α-OH-progesterone synthesized. The balance may be used for androgen synthesis. Labeled aldosterone also accumulated as an end product. Considerably more 11-deoxycorticosterone accumulated when cholesterol was used as the precursor. Both labeled aldosterone and cortisol (and traces of cortisone) accumulated. Hence several pathways of biosynthesis of corticosteroids are operational in the adrenal gland of the embryonic chick. Addition of ACTH to the incubation medium stimulated secretion of steroids into the medium, but did not effect levels within the glands.     

cAMP involvement in the control of corticosterone and aldosterone output in the adrenal of the frog (Rana berlandieri forreri)

The mechanism of ACTH action in the adrenal of the frog (Rana berlandieri forreri) was evaluated in vitro. Basal cAMP levels remained constant, but the total output of corticosterone and aldosterone increased with time. The rate of basal steroid output, however, decreased with time. ACTH, frog pituitary homogenate, and theophylline increased cAMP levels rapidly and temporally preceding increased outputs of corticosterone and aldosterone. The responses were rapid and dose-dependent. The role of cAMP in the frog adrenal steroid output is similar to that described in mammals and contrasts with that present in the crocodile. The mechanism of ACTH action in the frog adrenal involves cAMP in the stimulation of corticosterone and aldosterone output.     

Efficacy of aldosterone receptor antagonism in heart failure: Potential mechanisms

Results of the Randomized Aldactone Evaluation Study and the Eplerenone Post-acute Myocardial Infarction Heart Failure Efficacy and Survival Study indicate aldosterone receptor antagonism, together with angiotensin-converting enzyme inhibition and loop diuretics, is a most effective strategy in reducing risk for all-cause and cardiovascularrelated mortality and morbidity in patients with symptomatic heart failure. Responsible mechanisms are likely multifactoral. As a circulating hormone, aldosterone has well-known endocrine properties that contribute to the pathophysiology of congestive heart failure. This includes Na⁺ resorption at the expense of K⁺ excretion in such tissues as kidneys, colon, sweat, and salivary glands. Mg²⁺ excretion at these sites is likewise enhanced by aldosterone, whereas adrenal aldosterone secretion is regulated by extracellular Mg²⁺. Other endocrine actions of aldosterone receptor-ligand binding include: a reduction in biologically active cytosolic-free Mg²⁺, with intracellular Ca²⁺ loading in nonepithelial cells such as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions, including the choroid plexus, activity of the hypothalamic paraventricular nucleus, and autonomic nervous system. De novo generation of aldosterone within the cardiovasculature is recognized and findings suggest its auto/paracrine properties contribute to tissue repair. Each of these actions is interrupted by aldosterone receptor antagonism and therefore may contribute to its salutary response in heart failure.     

Corticosteroid receptors in the kidney of chick embryo II. Ontogeny of corticosterone receptor and cellular development

In this study the ontogeny of cytosol receptors for corticosterone in the chick embryo kidney was examined and then this ontogenic profile was compared with that of an index of cellular development, i.e., the enzyme ornithine decarboxylase (ODC). The corticosterone receptor concentration (n_max) increased by sevenfold from Day 12 to Day 15 of embryogenesis and then declined to its lowest level by the time of hatching (Day 21). Similar results were obtained when dexamethasone was used as ligand, except that the baseline values at Day 9 and 21 were higher than those found with corticosterone. An identical ontogenic profile was obtained when the results were corrected for the endogenous glucocorticoids present in the cytosol. This increase of the corticosterone receptor occurred simultaneously with the enhanced adrenal corticoid synthesis. The ODC also showed a marked increase and a rapid fall during chick embryogenesis, but the enzyme activity was at its maximum when the corticosterone receptor number was still low (Days 12 and 13) and quickly decreased by the time the receptors had reached their highest levels (Days 14 and 15). The lowest level of ODC was observed immediately before hatching. These results indicate that during chick embryogenesis adrenal corticoids may induce the development of the corticosteroid receptor and that such development may cause a suppression of ODC activity. This suppressive effect of glucocorticoids could represent a mechanism of hormonal action on the kidney.     

Corticosteroid-binding macromolecules in the salt-activated nasal gland of the domestic duck (Anas platyrhynchos).

The interaction of tritiated corticosterone and tritiated 11-dehydrocorticosterone with salt-activated nasal glands of the domestic duck was studied. Nasal gland cytosol (105,000g supernatant) bound corticosterone and 11-dehydrocorticosterone at 0° with apparent K_d values of 10^?9 and 10^?11M, respectively. The cytosols transformed [³H]corticosterone to [³H]11-dehydrocorticosterone (average transformation: 95% in 2 hr). Competition studies have shown that radioinert corticosterone is a more efficient competitor for cytosol binding sites than radioinert 11-dehydrocorticosterone. Cytosols labeled with [³H]corticosterone showed two major peaks following sucrose density gradient centrifugation: a heavy peak at 9–11S and a lighter peak at 3–4S. In sucrose gradients containing 0.4 M KCl, part of the heavier peak became transformed to the 3–4S form. Following incubation of [³H]corticosterone-labeled cytosols with crude nuclei, the cytosols became depleted of the label and the tritium activity, in the form of [³H]11-dehydrocorticosterone, accumulated in the nuclear Tris-soluble fraction and in the chromatin-bound (Tris-insoluble, 0.4 M KCl-soluble) fraction. Following the incubation of nasal gland slices with either [³H]corticosterone or [³H]11-dehydrocorticosterone, the cytosol, nuclear Tris-soluble fraction, and chromatin-bound fraction became labeled with [³H]11-dehydrocorticosterone only. Both steroids seemed to be taken up by the tissue slices at identical rates. Administration in vivo of [³H]corticosterone to a saltwater-maintained bird showed the accumulation of [³H]11-dehydrocorticosterone and, to a smaller extent, of [³H]corticosterone in the nasal gland intracellular fractions. It is suggested that the duck nasal gland is a corticosteroid target organ and the cytoplasmic protein-bound corticosterone is transported to the nucleus mostly as 11-dehydrocorticosterone in a manner similar to the intracellular transport of aldosterone in the rat and duck kidney.     

In vitro study of frog (Rana ridibunda Pallas) interrenal function by use of a simplified perifusion system. II. Influence of adrenocorticotropin upon aldosterone production.

In order to investigate various factors capable of regulating frog adrenal steroidogenesis, Rana ridibunda adrenal fragments were continuously perifused for 10 hr with amphibian culture medium (ACM). Aldosterone concentrations in the effluent medium were assayed without prior extraction by means of a sensitive and highly specific radioimmunoassay method. In all the experiments, large amounts of aldosterone were secreted even in the absence of ACTH stimulation. Aldosterone output paralleled temperature variations (5 to 30°). A highly significant correlation (r = 0.982; P < 0.01) was established between the outputs of corticosterone and aldosterone during this experiment. Infusion of frog distal lobe extract gave a dose-related response, with the highest dose (0.08 distal lobe eq/ml) yielding a 6.7-fold increase in aldosterone output. In this experiment, interrenal tissue produced two times as much aldosterone as corticosterone. When various dilutions of frog intermediate lobe extracts were tested upon interrenal fragments, a linear log-dose response in aldosterone production was observed for the lower doses and a plateau was reached for the higher doses (0.05 and 0.1 intermediate lobe eq/ml). Dibutyryl cyclic AMP, at a dose of 10 mM, led to a 3.18-fold increase in aldosterone output. These results suggest that aldosterone secretion is controlled by ambient temperature and by circulating levels of adrenocorticotropin. They demonstrate that, in frogs, output of aldosterone is two times higher than output of corticosterone. The aldosterone-corticosterone ratio is even larger after stimulation by high doses of ACTH. Finally, they confirm the presence of large concentrations of biologically active corticotropin in the intermediate lobe of frog pituitary.     

The role of adrenal steroids in the negative feedback control of the amphibian adrenal gland

Steroid-tipped hypothalamic probes containing either cholesterol, aldosterone, corticosterone, or betamethazone were found to significantly suppress plasma corticosterone levels in adult male Rana pipiens 24–48 hr postimplantation. Stress significantly elevated plasma corticosterone, and the stress response was inhibited by hypothalamic implants of both corticosterone and aldosterone.     

Stress and hypertensive disease: adrenals as a link. Experimental study on hypertensive ISIAH rat strain

Objective: Association between stress and hypertensive disease is still a matter of debate. Can stress be the cause of hypertensive disease and, if so, what mechanisms are involved? To clarify this question, the Inherited stress-induced arterial hypertensive rat strain (ISIAH rat strain) with a stress related arterial hypertension was developed by selection for the enhanced blood pressure response to 0.5 h restraint stress. The main intention of this work is to confirm that the adrenals are a main link between stress and hypertensive disease. Methods: Hypertensive ISIAH and normotensive WAG rats have been studied. The in vivo secretion rate of corticosterone, aldosterone, 11-Deoxycorticosterone (DOC), and 11-dehydrocorticosterone was measured in anesthetized rats by adrenal vein cannulation. The Dexamethasone/Adrenocorticotropic hormone (DEX/ACTH) test was performed and mRNA expression of Cyp11b1 and Cyp11b2 genes in adrenals was evaluated by real-time PCR. Results: An increased secretion rate of corticosterone and DOC and higher peripheral plasma aldosterone concentration in ISIAH rats were revealed. Response of plasma aldosterone to the surgical stress (adrenal vein cannulation) in the ISIAH rats was significantly higher. The increase of corticosterone and aldosterone in response to ACTH was also higher in hypertensive rats. The basal mRNA expression of both Cyp11b1 and Cyp11b2 genes was increased in the ISIAH rats. The ratio 11-dehydrocorticosterone/corticosterone in ISIAH rats was low which indicates the weakening of 11-beta-Hydroxysteroid dehydrogenase (11-beta-HSD) type 2 converting corticosterone to cortisone. Conclusion: ISIAH rats may serve as a living proof that stress may produce sustained hypertension, and genetically determined enhanced stress responsiveness of corticosterone and, especially, aldosterone may play a crucial role in the mechanism of hypertension development.     

Effects of leptin on the response of rat pituitary-adrenocortical axis to ether and cold stresses

Leptin is a hormone mainly secreted by the adipose tissue, which acts through specific receptors widely distributed in the body tissues, including hypothalamopituitary-adrenal axis. We have investigated the effects of a subcutaneous bolus injection of 5 nmol/kg leptin on the pituitary-adrenocortical function in both normal and ether- or cold-stressed rats. Blood concentrations of ACTH, aldosterone and corticosterone were measured by specific RIA 2 or 4 h after the leptin injection. Leptin administration to normal rats resulted in significant rises in the blood levels of ACTH, aldosterone and corticosterone at 2 h, but not at 4 h. Ether and cold stresses markedly increased hormonal blood concentrations at both 2 and 4 h. Leptin magnified ACTH response to ether stress at 2 h, but depressed it at 4 h, and enhanced aldosterone response at 2 h, without affecting corticosterone response. Leptin increased ACTH response to cold stress at both 2 and 4 h, without altering aldosterone and corticosterone responses. In light of these findings, we conclude that: (i) leptin evokes a middle transient activation of the pituitary-adrenocortical axis of rats under basal conditions; (ii) leptin inhibits the ACTH response to ether stress, but magnifies that to cold stress; and (iii) the leptin-evoked changes in the blood level of ACTH are not paralleled by significant modifications in the secretory activity of the adrenal cortex, which probably undergoes a maximal stimulation under stressful conditions.     

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.     

Formation of corticosteroids in vitro by interrenal tissue from the teleost fish, Coregonus clupeoides.

Adrenocortical tissue from the freshwater teleost, Coregonus clupeoides, was incubated with [¹⁴C] acetate and [³H] pregnenolone. Evidence was obtained for the formation of doubly labeled cortisol, cortisone, and deoxycortisol, and the 17-deoxycorticoids, corticosterone, deoxycorticosterone, and aldosterone. This corresponds very closely to the range of steroids isolated from circulating plasma in this species.Under conditions of incubation with dialysis, it was found that the tritiated products tended to be freely dialysable, whereas the [¹⁴C] products were significantly less so. The addition of Coregonus pituitary extract to the incubation medium caused both a release of [¹⁴C] steroid from the bound condition and a significant decrease in the yield of [¹⁴C] aldosterone; neither effect was seen with Synacthen. In all cases tritiated products were largely unaffected both in yield and dialysability.The results were consistent with the view that aldosterone is preferentially formed through a pathway involving bound intermediates. The native ACTH-sensitive bound pool of steroids and intermediates is penetrable by exogenous precursors occurring early in the biosynthetic pathway, such as [¹⁴C] acetate, but not by late precursors such as [³H] pregnenolone. The results are comparable with those obtained with other species, including the skink, Tiliqua rugosa and the zona glomerulosa (but not the inner zones) of the rat adrenal cortex.