Neuroendocrine profiling in inherited stress-induced arterial hypertension rat strain with stress-sensitive arterial hypertension

The functions of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems were studied in rats with inherited stress-induced arterial hypertension (ISIAH strain). A characteristic feature of the ISIAH strain is an increase in arterial blood pressure measured both under basal conditions and after restraint stress in particular. In the control ISIAH rats, the basal plasma ACTH concentration was slightly lower than that in the normotensive Wistar albino Glaxo (WAG) rats, and no differences were found in plasma corticosterone. However, the 0.5-h restraint stress produced higher activation of the adrenal cortex in the ISIAH rats. Gluco- and mineralocorticoid responses to the blood volume reduction stresses and ACTH and corticosterone responses to social stress were stronger in the ISIAH than in the control WAG rats. An increase in epinephrine content in adrenals in the basal state and enhanced response of the sympathetic adrenal medullary system to handling stress were observed in the ISIAH rats. Restraint stress produced significantly higher expression of genes encoding corticotropin-releasing hormone-mRNA in hypothalamus and proopiomelanocortin-mRNA in pituitary in the ISIAH than in the WAG rats. Restraint stress produced a decrease in glucocorticoid receptor (GR) gene expression (GR-mRNA) in hippocampus in the ISIAH, but not in the WAG rats. A persistent increase in tyrosine hydroxylase-mRNA in adrenals of the ISIAH rats was found. It is concluded that the ISIAH rat strain is an appropriate model of stress-sensitive hypertension with the predominant involvement of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems in its pathogenesis.     

Changes of arterial pressure and biosynthesis of corticosteroids in rats with neurogenic stress]

By way of a "psychogenic stimulation" (crowding for 1, 7 and 15 days) neurogenic hypertension was induced in male rats that developed in them within 11--15 days of the tsne of the stress. The biosynthesis of aldosterone, corticosterone, 11-dehydrocorticostrone and desoxycorticosterone by the adrenal glands of the rats in vitro from progesterone-14C appeared to greatly increased on the 1st day of stress. In 7 days of the beginning of stress the production of labelled corticosteroids fell to controlvalues (with the exception of 11-dehydrocorticosterone which production was growing still further). By the 15th day of stress reduction of the biosynthesis of aldosterone, corticosterone and desoxycorticosterone was observed, as well as normalization of the biosynthesis of 11-dehydrocorticosterone.     

Corticosteroid dynamics in the nonpregnant,pregnant, and postpartum spontaneously hypertensive rat

Factors responsible for hypertension in the spontaneously hypertensive rat (SHR) remain under investigation. As in human pregnancy complicated by essential chronic hypertension, the hypertension of the pregnant SHR subsides and returns postpartum. Because corticosteroid excess can cause hypertension, we examined several aspects of adrenocortical activity as potentially affecting the reported blood pressure profiles of nonpregnant, term pregnant, and postpartum SHR, using normotensive Wistar-Kyoto (WKY) rats as controls. We found that corticosterone levels were comparable in nonpregnant SHR and WKY rats, and unaffected by pregnancy. No differences were detected postpartum. Although pregnancy was accompanied by significant increases in plasma aldosterone levels, no interbreed differences were observed, which remained the case postpartum. Single adrenal cell secretion of aldosterone and corticosterone, as detected by reverse hemolytic plaque assay, yielded similar results in the pregnant and postpartum rat. Hormone responses to dietary manipulations in the nonpregnant and pregnant SHR and WKY suggest an important role for ACTH, and a lesser one for AII in the regulation of corticosteroids. In situ hybridization histochemistry, using a probe that detects both P450c11β and P450c11AS mRNA, revealed comparable message density and zonal distribution in adrenals from pregnant and nonpregnant SHR and WKY rats. Breed- and pregnancy-dependent differences in adrenal expression of P450scc, P450c11β, and P450c11AS were noted. In summary, our findings suggest that although some discrepancies exist in the aspects of adrenocortical activity examined, they are unlikely to be etiologic in the blood pressure profile observed in nonpregnant, pregnant, and postpartum SHR.     

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.     

Partial deficiency of adrenal 11-hydroxylase. A possible cause of primary hypertension

Results of supraphysiological adrenocorticotropic hormone (ACTH) stimulation of biosynthetic pathways of adrenal zona fasciculata indicate that a deficiency of 11-hydroxylase exists in patients with essential hypertension. The deficiency is suggested by the much greater stimulus of synthesis of deoxycorticosterone (DOC) and deoxycortisol in hypertensive subjects than in controls (p less than 0.001). No significant difference in the synthesis of cortisol, corticosterone, progesterone, 17-hydroxyprogesterone (17-OHP), and delta-4-androstenedione (D4) was observed between the two groups. The ratios for synthesis of DOC and corticosterone and for deoxycortisol and cortisol found in hypertensive patients were significantly higher than those found in controls (p less than 0.001); no significant difference was observed in the synthesis of 17-OHP and progesterone. The synthesis of DOC and deoxycortisol was not significantly correlated with either blood pressure or plasma renin activity. Plasma renin activity was significantly lower in hypertensive subjects than in normotensive subjects (p less than 0.0001), while no difference was found in aldosterone secretion between the two groups. The 11-hydroxylase deficiency in the adrenal zona fasciculata may be one of the genetic factors causing hypertension together with environmental factors (particularly salt intake and work-related stress). The investigation performed in our study may be useful for the evaluation of adrenal zona fasciculata enzymatic activities during the study of hypertensive patients.     

11beta-hydroxysteroid dehydrogenase and corticosteroid action in lyon hypertensive rats

Adrenocorticosteroid activity in Lyon hypertensive (LH) and low blood pressure (LL) rat strains differ in several respects. Abnormal activity of 11beta-hydroxysteroid dehydrogenase enzymes (11beta-HSD1 and 11beta-HSD2), which interconvert corticosterone and inactive 11-dehydrocorticosterone, might contribute to the LH phenotype by regulating corticosteroid hormone access to receptors. 11beta-HSD2 (expressed in kidney but not liver) prevents endogenous glucocorticoids from binding to mineralocorticoid receptors. 11beta-HSD1 (expressed in liver and kidney) favors active glucocorticoid formation from 11-dehydrocorticosterone. 11beta-HSD properties in LH and LL have been compared by several approaches: (1) 11betaHSD activities have been measured in vitro as corticosterone dehydrogenation and in vivo as interconversion of injected cortisol and cortisone; (2) the effects of cortisol and cortisone on urine electrolytes and volume have been measured; and (3) 11beta-HSD mRNA expression has been measured by in situ hybridization. 11beta-HSD2 enzyme activities in LH and LL rats were similar and urinary cortisone:cortisol ratios were not different after cortisol injection. Cortisol caused a natriuresis and kaliuresis in both strains, with a slightly reduced response in LH rats. Renal 11beta-HSD2 mRNA expression was slightly lower in LH rats. 11beta-HSD1 was less active in LH than LL rats: enzyme activities were lower in tissue extracts; urinary cortisone:cortisol was lower in LL rats after cortisone injections; cortisone increased urine volume in LL but not LH rats; and mRNA levels tended to be lower in LH tissues. We conclude that 11beta-HSD1 is impaired in LH rats. The LH phenotype of heavier adrenals, raised corticosterone, and reduced thymus weight is similar to that described for 11beta-HSD1 knockout mice.     

Adrenocortical activity in the newborn spontaneously hypertensive rat.

Blood pressure is reportedly elevated in the spontaneously hypertensive rat (SHR) neonate, the etiology of which remains unclear. Aberrations in the hypothalamic-pituitary-adrenal axis have been implicated, as it is well accepted that excess corticosteroids are associated with hypertension. We examined aspects of adrenocortical activity in the neonatal SHR 1 to 21 days old and its normotensive genetic control, the Wistar-Kyoto rat (WKY). We found a fourfold greater abundance of P450scc mRNA in adrenals of SHR versus WKY day 1 neonates, and increasing but comparable abundance of adrenal P450c11B mRNA on neonatal days 1 to 21. The pattern of P450c11AS mRNA expression was distinctly different in the adrenals of SHR and WKY neonates; the relative abundance of this mRNA in SHR increased 15-fold over the 21-day period examined, whereas that in WKY remained fairly stable. RT-PCR for the presence/abundance of adrenal P450c11B3 mRNA showed absence in day 1 SHR and WKY, comparable abundances on neonatal days 7 and 14, and a distinctly greater abundance in the day 21 SHR adrenals. Peripheral corticosterone levels were threefold greater in the day 1 SHR neonate; aldosterone levels were elevated in both the SHR and WKY day 1 neonate. Thereafter, corticosterone and aldosterone levels were comparable on days 7, 14, and 21, although the anticipated depression in circulating corticosterone levels typical of the stress hyporesponsive period was noted in both SHR and WKY neonates. Although patterns of adrenocortical activity differ in the newborn SHR and WKY rat, our findings do not support an etiologic role for corticosteroids in the reported hypertension of the SHR. However, observed differences in corticosteroid profiles may augment or have a permissive effect upon the etiologic factor(s).     

Effect of various stressors on the blood ACTH and corticosterone concentration in normotensive Wistar and spontaneously hypertensive Wistar-Kyoto rats

The role of the sympathetic nervous system (SNS) and the hypothalamo-pituitary-adrenal (HPA) axis in the stress response is well documented. The imbalance in a central and peripheral SNS activity accompanied by the HPA hyperresponsivity has been observed in essential and experimental hypertension. The spontaneously hypertensive rats (SHR) are extensively used in studying mechanisms of the essential hypertension. The blood ACTH and corticosterone concentration was examined in spontaneously hypertensive (Wistar-Kyoto) and normotensive (Wistar) adult male rats exposed to acute cold (2h) or immobilization (2h) stress as well as chronic (21days) isolation stress or their combination. The present results show that SHR in basal conditions have higher blood ACTH and corticosterone level as compared to the normotensive rats. Both the acute exposure to cold and immobilization stress induced a higher increment in SHR plasma ACTH in respect to Wistar rats. The similar pattern of ACTH response occurred when SHR were previously chronically isolated and acutely exposed to both applied stressors. Surprisingly, corticosterone concentration did not differ between control rats with or without 21days isolation or those exposed to a cold or immobile acute stressor.     

Abnormalities in the hypothalamo-pituitary-adrenal axis in spontaneously hypertensive rats during development of hypertension

Abnormalities in the hypothalamo-pituitary-adrenal axis in spontaneously hypertensive rats (SHR) during development of hypertension were investigated using in vivo and in vitro methods. Plasma ACTH responses to hemorrhage and ether stress were significantly smaller in 7-week-old SHR than in age-matched Wistar-Kyoto rats (WKY), while plasma corticosterone baseline levels and its response to stress were greater in SHR than in WKY. There was no significant difference in the plasma ACTH response to ether stress between bilaterally adrenalectomized SHR and WKY replaced with a 25% corticosterone pellet for 6 days. Adrenalectomy prevented the development of hypertension in SHR; however, corticosterone replacement restored hypertension. Plasma ACTH showed a smaller response to iv CRH injection in SHR than in WKY, while the ACTH response to arginine vasopressin was not different between SHR and WKY. CRH concentrations in the median eminence, posterior pituitary, and cerebral cortex were lower in SHR than in WKY, while the CRH concentration in the median eminence was not different in SHR and WKY when they were adrenalectomized with or without corticosterone replacement. Basal in vitro CRH release from hypothalamic tissue was reduced in SHR, while CRH release in response to 56 mM KCl was not different in SHR and WKY. These results suggest that adrenocortical function is enhanced in young SHR, that reduced ACTH response to stress and exogenous CRH in SHR may be ascribed to higher plasma corticosterone levels, and that corticosterone is essential for the development of hypertension in SHR.     

Control of aldosterone secretion in the spontaneously hypertensive rat.

Adrenal secretion rates of aldosterone, corticosterone, and deoxycorticosterone were studied sequentially in the spontaneously hypertensive rat and the normotensive Kyoto Wistar rat. Steroid secretion was studied at three different ages: 7-8, 11-13, and 22-25 weeks. Also, peripheral plasma levels of aldosterone and plasma renin activity were determined in both the spontaneously hypertensive and the normotensive rats at 7-8 weeks of age. Aldosterone secretion was elevated markedly in dexamethasone-morphine-treated spontaneously hypertensive rats at both 7-8 and 11-13 weeks of age but was not significantly different from control in 22-25-week-old spontaneously hypertensive rats. No statistically significant differences in corticosterone or deoxycorticosterone secretion rates were observed between the spontaneously hypertensive rats and the normotensive Kyoto Wistar controls; however, the data suggested that dexamethasone did not suppress adrenocorticotropic hormone in the 7-8- and 11-13-week-old spontaneously hypertensive rats to the same extent that it did in the normotensive Kyoto Wistar rats. Therefore, aldosterone secretion was reexamined in acutely hypophysectomized 7-8-week-old rats to eliminate completely the influence of the anterior pituitary; no differences in aldosterone, corticosterone, or deoxycorticosterone secretion rates were observed between hypophysectomized spontaneously hypertensive rats and normotensive Kyoto Wistar rats. Moreover, aldosterone secretion in the hypophysectomized 7-8-week-old spontaneously hypertensive rats was reduced markedly compared with that in the intact 7-8-week old spontaneously hypertensive rats, thus confirming the importance of the pituitary in these animals. Determinations of peripheral plasma aldosterone concentration and plasma renin activity in unstressed 7-8-week-old spontaneously hypertensive and normotensive rats revealed that both parameters were depressed significantly in the spontaneously hypertensive rats. Thus, the present data indicate that the renin-angiotensin-aldosterone system is suppressed in the spontaneously hypertensive rat but do not suggest that the system is critically involved in the hypertensive process in these animals     

Response of several adrenal steroids to ACTH stimulation in essential hypertension.

Plasma concentrations of progesterone (P), deoxycorticosterone (DOC), 17-hydroxyprogesterone (17-OH P), corticosterone (B), deoxycortisol (S), cortisol (F), and aldosterone were measured in 8 control subjects and in 10 patients with low and normal renin essential hypertension (EH) before and 4 and 8 h after an iv infusion of 25 units of ACTH. Secretion rates of 18-hydroxy-11-deoxycorticosterone (18-OH DOC) were measured for the 24 h prior to and the day of the ACTH infusions. The hypertensive patients had significantly higher plasma levels of aldosterone, DOC and S after ACTH than the controls, whereas plasma B levels were significantly lower. The low renin subgroup considered separately had significantly higher plasma levels of aldosterone and DOC than controls, and higher levels of B and lower levels of F than the normal renin subgroup in response to ACTH. Although not significantly different, the plasma levels of P and the secretion rate of 18-OH DOC tended to be higher, and plasma 17-OH P and F levels lower after ACTH in patients with EH than in controls. The low renin subgroup tended to have the highest plasma S levels and 18-OH DOC secretory rates and lowest F levels. Estimations of adrenal 11beta-hydroxylating efficiency in response to ACTH in patients and controls by plasma steroid ratios revealed significantly lower B/DOC ratios in both low and normal renin patients compared to controls, supported by somewhat lower F/S ratios in these patients, especially those in the low renin subgroup. Altered 17-hydroxylating efficiency seen by significantly lower 17-OH P/P ratios were also found in those with EH, supported by somewhat lower F/B and S/DOC ratios in these patients, agian especially in the low renin subgroup. These data are compatible with a pattern of altered adrenocortical steroid biosynthesis in essential hypertension bearing features similar to adrenal 11beta and 17alpha-hydroxylation deficiencies.     

Stress,Genes, and Hypertension. Contribution of the ISIAH Rat Strain Study

Purpose of Review

Acute psychoemotional stress is one of the causes of a sharp increase in blood pressure. However, the question if the stress may promote the hypertensive disease development is still open. This review aims, firstly, to show that the genetically determined enhanced responsiveness to stress is linked to sustained hypertension development and, secondly, to characterize the main physiological mechanisms and genetic factors implicated in the pathogenesis of stress-sensitive hypertension.

Recent Findings

Recent findings helped to characterize the main neuroendocrine mechanisms and the specificity of the genetic background contributing to the stress-sensitive hypertension development in the ISIAH rats.

Summary

The ISIAH rat strain, which is an original model of the stress-sensitive arterial hypertension, can be considered as “living” proof that the genetic predisposition to increased stress-reactivity can lead to the development of persistent stress-dependent arterial hypertension. The ISIAH rat strain is characterized by the genetically determined enhanced response of the neuroendocrine and renal regulatory systems to stress and is a suitable model that allows one to explore the genetic and physiological mechanisms involved in stress-sensitive hypertension development. There are common genetic loci (QTLs) associated with both basal and stress-induced blood pressure (BP) levels as well as QTLs associated with BP and other traits, which may be related to hypertension development in ISIAH rats. Multiple genes differentially expressed in the target organs/tissues of hypertensive ISIAH and normotensive control rats are associated with many biological processes and metabolic pathways involved in stress response and arterial hypertension. The genotype of ISIAH rats is characterized by numerous specific and common SNPs as compared with other models of hypertensive rats. The results of the studies are valuable for the search for genetic markers specific for stress-induced arterial hypertension, as well as for the selection of new molecular targets that may be potentially useful for prevention and/or therapy of hypertensive disease.

     

The role of the adrenal gland in hypertensive transgenic rat TGR(mREN2)27.

The TGR(mREN2)27 is a new monogenetic rat model in hypertension research. As the mouse Ren-2d renin gene is integrated into their genome, they develop fulminant hypertension between 5 and 15 weeks of age, with blood pressure maxima of 300 mm Hg. Their plasma renin-angiotensin system (RAS) is suppressed, but the transgene is highly expressed in the adrenal gland, so we investigated its possible role in steroid metabolism and the pathogenesis of hypertension. During the phase of hypertension development (between 6-18 weeks), the urinary excretion of deoxycorticosterone (DOC), corticosterone (B), 18-hydroxycorticosterone, and aldosterone is 1.5- to 2.5-fold elevated compared with that in Sprague-Dawley (SD) rats (P less than 0.0005) despite the suppressed plasma RAS. Moreover, the adrenal gland in TGR(mREN2)27 shows an increased maximal response to ACTH stimulation in regard to urinary excretion of DOC (after ACTH, 244 +/- 42 ng/24 h in TGR; 62 +/- 10 ng/24 h in SD; P less than 0.0005) and B (after ACTH, 5144 +/- 346 ng/24 h in TGR; 2607 +/- 324 ng/24 h in SD; P less than 0.0005). Additionally, plasma prorenin in TGR was stimulated more than 10-fold, indicating transgene regulation by ACTH. Since spironolactone treatment did not lower the blood pressure in TGR, hypertension solely due to hypermineralocorticoism is unlikely. Our results indicate that the adrenal steroid metabolism is markedly stimulated in young TGR, and the absolute increase in urinary DOC and B after ACTH injections is enhanced, possibly due to a stimulated local intraadrenal RAS.     

Phenotypic consequences of variation across the aldosterone synthase and 11-beta hydroxylase locus in a hypertensive cohort: data from the MRC BRIGHT Study

Background Aldosterone is an important cardiovascular hormone; 15% of hypertensive subjects have alteration in aldosterone regulation, defined by a raised ratio of aldosterone to renin (ARR). Studies of the aldosterone synthase gene (CYP11B2) have focused on a single nucleotide polymorphism in the 5′promoter region (–344 C/T). In normotensive subjects, the T allele associates with raised levels of the 11‐deoxysteroids, deoxycorticosterone and 11‐deoxycortisol which are substrates for 11β‐hydroxylase, encoded by the adjacent and homologous gene, CYP11B1. We have speculated that this altered 11β‐hydroxylase efficiency leads to increased ACTH drive to the adrenal gland to maintain cortisol production and reported herein the association between the –344 C/T single nucleotide polymorphism (SNP) and adrenal steroid production in subjects with essential hypertension. Methods The CYP11B2–344 C/T polymorphism was genotyped and urinary excretion of adrenal steroid metabolites was measured (by GCMS) in 511 unrelated hypertensives from the Medical Research Council (MRC) British Genetics of Hypertension (BRIGHT) study. Results Thirty‐five per cent of subjects were homozygous for the –344T allele whilst 16% were CC homozygotes. There was no difference in cortisol excretion rate between the two genotype groups but the index of adrenal 11β‐hydroxylation (ratio of tetrahydrodeoxycortisol/total cortisol) was significantly higher in the TT group (P < 0·005) than in the CC group. Excretion rates of the major urinary metabolite of aldosterone (tetrahydroaldosterone) correlated strongly with the ACTH‐regulated steroids, cortisol (r = 0·437, P < 0·0001) and total androgen metabolites (r = 0·4, P < 0·0001) in TT but not CC subjects. Conclusions Hypertensives homozygous for the –344 T allele of CYP11B2 demonstrate altered 11β‐hydroxylase efficiency (CYP11B1); this is consistent with the hypothesis of a genetically determined increase in adrenal ACTH drive in these subjects. The correlation between excretion of aldosterone and cortisol metabolites and suggests that, in TT subjects, ACTH exerts an important common regulatory influence on adrenal corticosteroid production in subjects with hypertension.     

Evidence for an unidentified ACTH-induced steroid hormone causing hypertension.

The hypothesis that hyperaldosteronism is not the sole cause of hypertension in dexamethasone-suppressible hyperaldosteronsim was tested in an 18-year-old male. After six years of little or no treatment, the hypertension and mild hyperaldosteronism were promptly decreased by a small dose of dexamethasone. During dexamethasone treatment, when aldosterone secretion was suppressed to less than normal and he was normotensive, steroids were given by constant infusion in an attempt to reproduce the hypertension of the dexamethasone-free state. Neither five days of aldosterone or 18-hydroxydesoxycorticosterone (18-OH-DOC) at 1 mg/day, nor desoxycorticosterone (DOC) at 30 mg/day caused hypertension. However, sodium retention and potassium loss was observed during aldosterone and DOC infusion. Hypertension was produced within five days during infusion with ACTH or oral metyrapone. The hypertensive effect of the latter was abolished by addition of aminoglutethimide treatment. These studies suggest that a steroid other than aldosterone, 18-OH-DOC, or DOC may be the cause of the ACTH-induced hypertension in this patient. The aminoglutethimide data suggest that the ACTH effect on blood pressure is due to a steroid, and the metyrapone studies suggest that the steroid may be an 11-desoxysteroid. Urine and blood collected under ACTH stimulation and metyrapone treatment may be a rich source from which we may characterize this hormone.     

Mineralocorticoid secretion in essential hypertension with normal and low plasma renin activity.

In 19 control subjects, 33 patients with essential hypertension and normal plasma renin activity (PRA) and 11 patients with low PRA, secretory rates of 18-hydroxy-11-deoxy-corticosterone (18-OH DOC), 11-deoxycorticosterone (DOC) and corticosterone were measured. Patients with low PRA were significantly older and had higher arterial pressure and slightly lower plasma potassium levels than patients with normal PRA. Mean 18-OH DOC secretion rate was higher in patients with normal PRA (603 +/- 112 SEM mug/24 hr) than in control subjects (219 +/- 19) and considerably higher (P less than 0.001) in patients with low PRA (1800 +/- 472). DOC and corticosterone secretion rates were within normal limits in most hypertensive patients. Plasma aldosterone was significantly higher in the hypertensive population than in control subjects whereas no significant difference was observed between the low- and normal-renin groups. A significant (P less than 0.01) mutual positive correlation was found between the secretion rates of 18-OH DOC, DOC and corticosterone in patients with low plasma renin activity. In contrast, there was no correlation between the secretion rates of the three mineralocorticoids in control subjects and patients with normal plasma renin activity. These data suggest a biosynthetic variation of the mineralocorticoid pathways in essential hypertension.     

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.     

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.