Interactions between 11beta-hydroxysteroid dehydrogenase and COX-2 in kidney

The syndrome of apparent mineralocorticoid excess (SAME) is an autosomal recessive form of salt-sensitive hypertension caused by deficiency of the kidney type 2 11beta-hydroxysteroid dehydrogenase (11betaHSD2). In this disorder, cortisol is not inactivated by 11betaHSD2, occupies mineralocorticoid receptors (MRs), and causes excessive sodium retention and hypertension. In renal medulla, prostaglandins derived from cyclooxygenase-2 (COX-2) stimulate sodium and water excretion, and renal medullary COX-2 expression increases after mineralocorticoid administration. We investigated whether medullary COX-2 also increases in rats with 11betaHSD2 inhibition and examined its possible role in the development of hypertension. 11betaHSD2 inhibition increased medullary and decreased cortical COX-2 expression in adult rats and induced high blood pressure in high-salt-treated rats. COX-2 inhibition had no effect on blood pressure in control animals but further increased blood pressure in high-salt-treated rats with 11betaHSD2 inhibition. COX-1 inhibition had no effect on blood pressure in either control or experimental animals. 11betaHSD2 inhibition also led to medullary COX-2 increase and cortical COX-2 decrease in weaning rats, primarily through activation of MRs. In the suckling rats, medullary COX-2 expression was very low, consistent with a urinary concentrating defect. 11betaHSD2 inhibition had no effect on either cortical or medullary COX-2 expression in the suckling rats, consistent with low levels of circulating corticosterone in these animals. These data indicate that COX-2 plays a modulating role in the development of hypertension due to 11betaHSD2 deficiency and that 11betaHSD2 regulates renal COX-2 expression by preventing glucocorticoid access to MRs during postnatal development.     

Extraction of 11 beta-hydroxysteroid dehydrogenase from rat liver microsomes by detergents

In these studies our goal was to solubilize the microsomal enzyme, 11 beta-hydroxysteroid dehydrogenase (11-HSD) as the first step in its purification. Enzyme was extracted from rat liver microsomes with representative detergents (Zwittergents, Tritons, modified sterols). Oxidation-reduction (O-R) ratios of extracts varied with detergent used and ranged from 0.18 (CHAPS) to 3.8 (Zwittergent 3-14) relative to a ratio of 1.7 in intact microsomes. All detergents solubilized 11-HSD using lack of sedimentation during high speed centrifugation as criterion. With Triton DF-18 and Triton X-100, optimum extraction of 11-HSD occurred in the detergent-protein ratio range of 0.1 to 0.2 O-R ratios decreased with increased Triton X-100, but were constant as Triton DF-18 was varied. The pH optimum of enzyme extraction was 9 at a detergent-protein ratio of 0.05 and 7.5-8.0 at a ratio of 0.2. Sodium chloride increased enzyme extraction by detergents; in the absence of detergent, salt extracted protein, but not enzyme. In aqueous solution at 0 degrees C or -15 degrees C, microsomal 11-oxidation activity rose within 24 h, then decreased; reductase activity consistently decreased. Oxidation and reduction activities were inversely related in the microsomal bound enzyme. No relationship between these activities appeared in detergent-solubilized enzymes. Possible mechanisms to account for the unexpected behavior of this enzyme are discussed.     

Expression of human kidney 11beta-hydroxysteroid dehydrogenase (11-HSD2) in bacteria

The kidney isozyme of 11beta-hydroxysteroid dehydrogenase (11-HSD2) protects the mineralocorticoid receptor from spurious activation by glucocorticoids. To explore structure-function relationships, human 11-HSD2 cDNA was subcloned into the bacterial expression vector, pET25b. E. coli transformed with wild-type cDNA produced active enzyme that retained biochemical characteristics of the native protein. The addition of 6 histidine residues to the C-terminus of the wild-type enzyme (11-HSD2/His) increased activity 2-fold. Whereas wild-type activity was almost completely sedimented following 100,000g centrifugation, 10-30% of total activity of 11-HSD2/His remained in the supernatant. The 11-HSD2 isozyme normally contains three N-terminal hydrophobic domains. Mutant 11-HSD2/His possessing a single hydrophobic domain retained partial activity, but elimination of all domains inactivated the enzyme. Thus, the N-terminal hydrophobic domains are essential for complete activity of 11-HSD2 but association with an intact cell membrane is not.     

The type I and type II 11beta-hydroxysteroid dehydrogenase enzymes.

Local tissue concentrations of glucocorticoids are modulated by the enzyme 11β-hydroxysteroid dehydrogenase which interconverts cortisol and the inactive glucocorticoid cortisone in man, and corticosterone and 11-dehydrocorticosterone in rodents. The type I isoform (11β-HSD1) is a bidirectional enzyme but acts predominantly as a oxidoreductase to form the active glucocorticoids cortisol or corticosterone, while the type II enzyme (11β-HSD2) acts unidirectionally producing inactive 11-keto metabolites. There are no known clinical conditions associated with 11β-HSD1 deficiency, but gene deletion experiments in the mouse indicate that this enzyme is important both for the maintenance of normal serum glucocorticoid levels, and in the activation of key hepatic gluconeogenic enzymes. Other important sites of action include omental fat, the ovary, brain and vasculature. Congenital defects in the 11β-HSD2 enzyme have been shown to account for the syndrome of apparent mineralocorticoid excess (AME), a low renin severe form of hypertension resulting from the overstimulation of the non-selective mineralocorticoid receptor by cortisol in the distal tubule of the kidney. Inactivation of the 11β-HSD2 gene in mice results in a phenotype with similar features to AME. In addition, these mice show high neonatal mortality associated with marked colonic distention, and remarkable hypertrophy and hyperplasia of the distal tubule epithelia. 11β-HSD2 also plays an important role in decreasing the exposure of the fetus to the high levels of maternal glucocorticoids. Recent work suggests a role for 11β-HSD2 in non-mineralocorticoid target tissues where it would modulate glucocorticoid access to the glucocorticoid receptor, in invasive breast cancer and as a mechanism providing ligand for the putative 11-dehydrocorticosterone receptor. While previous homologies between members of the SCAD superfamily have been of the order of 20–30% phylogenetic analysis of a new branch of retinol dehydrogenases indicates identities of >60% and overlapping substrate specificities. The availability of crystal structures of family members has allowed the mapping of conserved 11β-HSD domains A–D to a cleft in the protein structure (cofactor binding domain), two parallel β-sheets, and an -helix (active site), respectively.     

Streptozotocin-induced diabetes in the pregnant rat reduces 11 beta-hydroxysteroid dehydrogenase type 2 expression in placenta and fetal kidney

Several epidemiological and animal studies have shown that the offsprings of diabetic mothers have higher incidences of glucose intolerance, obesity, insulin resistance, and hypertension in later life. It is well known that glucocorticoid metabolism plays a crucial role on several adult disease originated from fetal environment. The aim of this study was to investigate the relation between diabetic pregnancy and glucocorticoid metabolism of both mother and fetus, focusing on the 11 beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2. A model of diabetic pregnancy was made by intravenous injection of streptozotocin (35 mg/kg body weight) to Sprague-Dawley rats, and blood and tissue samples were collected on day 20 of pregnancy. In the diabetic group, expression of 11 beta-hydroxysteroid dehydrogenase type 2 in placentas and fetal kidneys was decreased remarkably. Corticosterone levels of diabetic mothers were lower than those of control rats. Despite the differences in maternal corticosterone levels, fetal levels of corticosterone did not differ between the groups. Our results lend support to the concept that diabetic pregnancy imprints glucocorticoid regulation in these fetuses, which may contribute to their increased incidence of higher blood pressure as adults.     

Regulation by dexamethasone of the 3 beta-hydroxysteroid dehydrogenase activity in adult rat Leydig cells.

The effect of long-term in vitro treatment with dexamethasone, insulin and/or LH on the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity and the testosterone level was examined in cultures of Leydig cells from adult rats. A rapid and simple method for measuring the 3 beta-HSD activity has been developed, in which the NADH, generated by 3 beta-HSD, reduced nitroblue tetrazolium to a product with absorption maximum at 560 nm. Km for the reaction was 8.1 microM and Vmax was 12.7 nmol/min x mg protein. Addition of 0.1 or 1 microM dexamethasone for 44 h decreased the 3 beta-HSD activity to 83% and the basal testosterone level to 64% of control value after 22 and 44 h of culture. Addition of 1 nM insulin inhibited the 3 beta-HSD activity to 90% after 44 h of culture, whereas the testosterone level was increased after 3 h. Addition of 0.1 ng/ml LH did not affect the 3 beta-HSD activity in Leydig cells from adult rats. Concomitant treatment of the cells with dexamethasone and insulin inhibited the 3 beta-HSD activity to 74%, indicating an additive effect, whereas no additive effect on the testosterone level was observed. The results demonstrate that the 3 beta-HSD activity can be measured in a rapid and reliable way by measuring the reduction of nitroblue tetrazolium. Furthermore, the results suggest that dexamethasone acts on 3 beta-HSD through a mechanism different from that of insulin, as an additive effect was observed.     

Ontogenesis of oxidative reaction of 17beta-hydroxysteroid dehydrogenase and 11beta-hydroxysteroid dehydrogenase in rat Leydig cells,a histochemical study

The enzyme 17beta-hydroxysteroid dehydrogenase is required for the synthesis and 11beta-hydroxysteroid dehydrogenase for the regulation of androgens in rat Leydig cells. This histochemical study describes ontogenetic changes in distribution and intensity of these enzymes in Leydig cells from postnatal day (pnd) 1-90. Using NAD or NADP as the cofactor, 17beta-hydroxysteroid dehydrogenase (substrate: 5-androstene-3beta,17beta-diol) peaks were observed on pnd 16 for fetal Leydig cells and on pnd 19 and 37 for adult Leydig cells. Between pnd 13 and 25 the fetal cells showed a higher intensity for the 17beta-enzyme than the adult cells; more fetal Leydig cells were stained with NADP, whereas more adult cells were positive with NAD on pnd 13 and 16. A nearly identical distribution of 11beta-hydroxysteroid dehydrogenase (substrate: corticosterone) was observed with NAD or NADP as the cofactor; the reaction was present from pnd 31 onwards, first in a few adult Leydig cells and later in almost all these cells homogeneously. The ontogenetic curves of the two enzymes show an inverse relationship. To conclude: (1) Generally, a stronger reaction for 17beta-hydroxysteroid dehydrogenase is shown with NAD as cofactor than with NADP; using NADP, fetal Leydig cells show a stronger staining than adult Leydig cells. (2) The data possibly support the notion of a new isoform of 11beta-hydroxysteroid dehydrogenase in addition to types 1 and 2.     

11 beta-hydroxysteroid dehydrogenase activity in the mammary gland

Levels of 11 beta-hydroxysteroid dehydrogenase activity in mammary gland homogenates from pregnant and lactating Sprague-Dawley rats were determined by incubation with [3H]corticosterone under standard conditions, followed by thin-layer chromatography of incubated media. Enzyme activity was high in virgin and pregnant rats, but fell soon after parturition, suggesting a possible role for this enzyme in the co-ordinate regulation of glucocorticoid effects on milk protein synthesis.     

Regulation of expression of male-specific rat liver microsomal 3 beta-hydroxysteroid dehydrogenase

In the steroidogenic pathways present in the gonads and adrenal cortex, 3 beta-hydroxysteroid dehydrogenase isomerase (3 beta HSD) is a key enzyme which controls the formation of delta 4-3-ketosteroids from delta 5-3 beta-hydroxysteroids. Herein, we used an antibody against human placental 3 beta HSD and a rat testicular 3 beta HSD cDNA probe to study the expression of rat liver 3 beta HSD mRNA and protein. Rat liver microsomal 3 beta HSD activity has been previously reported to exhibit a significant sex difference, with much higher activity in the male. We have shown an age-dependent increase in levels of immunoreactive 3 beta HSD through the time of maturation of the male rat. The immunoreactive protein, of similar molecular size to the human placental and rat testicular 3 beta HSD, was localized to the microsomal fraction of liver and was concentrated in pericentral locations. Immunoreactive protein was not detected in liver of immature (before 25 days of age) rats of either sex or in adult female liver. Northern blot analysis of liver and testicular RNA with a rat testicular 3 beta HSD cDNA probe revealed the presence of a 1.6-kilobase mRNA species in addition to the major 2.1-kilobase mRNA species in adult male liver, neither of which was detected in immature or adult female liver RNA. Hypophysectomy of female rats or treatment with testosterone implants caused induction of liver 3 beta HSD protein, while continuous infusion of GH to male rats decreased the level of 3 beta HSD protein. Similarly, the levels of the mRNA species were decreased after GH treatment. Using [3 alpha-3H]dehydroepiandrosterone as substrate for 3 beta HSD activity, we determined the apparent Km for liver microsomal NAD(+)-dependent 3 beta HSD activity to be 20 microM in both adult male and female liver and was much greater than the Km of rat Leydig tumor 3 beta HSD activity (0.2 microM). Liver 3 beta HSD activity was inhibited by trilostane, a proven inhibitor of gonadal and adrenal 3 beta HSD activity. A rat liver 3 beta HSD cDNA was isolated from a male liver cDNA library that was closely related to the type II 3 beta HSD form of rat ovary but different from type III liver 3 beta HSD. The enzyme obtained upon expression of this cDNA had properties characteristic of male-specific NAD(+)-dependent liver microsomal 3 beta HSD (i.e. high apparent Km for dehydroepiandrosterone) and distinct from those of the high affinity gonadal type I 3 beta HSD.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inhibition of 11 beta-hydroxysteroid dehydrogenase type 2 by dithiocarbamates

Dithiocarbamates (DTCs), important therapeutic and industrial chemicals released in high quantities into the environment, exhibit complex chemical and biological activities. Here, we demonstrate an effect of DTCs on glucocorticoid action due to inhibition of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) type 2, converting cortisol to cortisone in the kidney, but not 11 beta-HSD1, catalyzing the reverse reaction in liver and adipose tissue. Thus, DTCs may locally increase active glucocorticoid concentrations. Preincubation with the DTC thiram abolished 11 beta-HSD2 activity, suggesting irreversible enzyme inhibition. The sulfhydryl protecting reagent dithiothreitol blocked thiram-induced inhibition and NAD+ partially protected 11 beta-HSD2 activity, indicating that DTCs act at the cofactor-binding site. A 3D-model of 11 beta-HSD2 identified Cys90 in the NAD(+)-binding site as a likely target of DTCs, which was supported by a 99% reduced activity of mutant Cys90 to serine. The interference of DTCs with glucocorticoid-mediated responses suggests a cautious approach in the use of DTCs in therapeutic applications and in exposure to sources of DTCs such as cosmetics and agricultural products by pregnant women and others.     

Regulation of ovarian 17 beta-hydroxysteroid dehydrogenase activity by gonadotropin

Serum testosterone levels are elevated prior to the lutropin surge, and decline abruptly following the release of endogenous lutropin. To investigate this phenomenon, the activity of 17 beta-hydroxysteroid dehydrogenase, the enzyme directly related to testosterone production from androstenedione, was measured. This was done in immature rats in which follicular maturation and ovulation were induced by pregnant mare serum gonadotropin administration. It appears that the effect of the gonadotropin on the enzyme activity is sharply divided into two phases that match with the follicular and the luteal phases. One day following gonadotropin administration, there was already a 7.67-fold increase in the original activity which further increased 48 h following hormone administration. At the peak of the lutropin surge, when follicular development is at its maximum, a 18.44-fold increase was measured. The activity fell abruptly 10 h following ovulation, at a time when fresh corpora lutea are already present in the ovary. It seems that the elevation of serum testosterone followed by its abrupt decline, is directly related to the increased and decreased ovarian 17 beta-hydroxy-steroid dehydrogenase activity. The possible importance of the observed changes to the mechanism of the onset of puberty are discussed.     

Glycyrrhetinic acid bound to 11 beta-hydroxysteroid dehydrogenase in rat liver microsomes.

A binding protein which exhibits high affinity to [3H]glycyrrhetinic-acid in the rat liver microsomal fraction was solubilized with 0.2% Triton DF-18 and then purified to homogeneity. The equilibrium dissociation constant of the [3H]glycyrrhetinic-acid binding reaction and the maximal concentration for the binding of the purified protein, as determined by Scatchard plot analysis, were 27.6 nM and 7.79 nmol/mg protein, respectively. The molecular mass of the subunit (34 kDa) and 30 amino acids of N-terminal sequence of the purified protein were entirely the same as those of the reported 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). In each purification step, the recovery and purification (fold) of the glycyrrhetinic-acid binding activity corresponded to the values of 11 beta-HSD activity. These results show that the purified [3H]glycyrrhetinic-acid binding protein is 11 beta-HSD. From the molecular mass of 11 beta-HSD (135 kDa) and the maximal concentration of the binding site, it was calculated that one glycyrrhetinic acid molecule binds to one 11 beta-HSD molecule. The inhibitory effects of various glycyrrhetinic-acid derivatives on [3H]glycyrrhetinic acid binding and 11 beta-HSD activity indicate that the C30-carboxyl and C11-carbonyl groups of glycyrrhetinic acid are the principal structures for the 11 beta-HSD inhibition.     

11beta-hydroxysteroid dehydrogenase functions reversibly as an oxidoreductase in the rat hippocampus in vivo

The localization in the brain and metabolism of 3H-labeled corticosterone (B) and 11-dehydrocorticosterone (A) of high specific radioactivity was determined after stereotaxic injection into the hippocampus of anesthetized rats. [3H]B was cleared very rapidly with, on average, only about 7% being recovered after 5 min and 0.5% after 30 min. Most of this 3H-radioactivity was localized in the area surrounding the site of injection with little diffusion to adjacent areas. These findings make it possible to compare the short term metabolism of [3H]A and [3H]B in different lobes of the hippocampus in the same animal and establish their local equilibrium point in vivo. Under these conditions, about 5% conversion of each steroid to the other was observed in contrast to the situation in cultured hippocampal cells where 11beta-hydroxysteroid dehydrogenase (11-HSD) has been shown by others to act primarily as a reductase catalyzing the conversion of A to B. This method can also be used to study the effect of inhibitors such as 11alpha-hydroxyprogesterone, applied locally in the brain, on the metabolism of corticosteroids. The rate of conversion [3H]B or [3H]A to their dihydro- and tetrahydro-derivatives capable of modulating the GABAa receptor in the hippocampus was much lower than their interconversion. Thus, factors which influence the direction of the 11-HSD catalyzed reaction are important in regulating not only salt appetite and blood pressure but also the levels of neuroactive metabolites of corticosterone.     

Inhibition of human and rat 11beta-hydroxysteroid dehydrogenase type 1 by 18beta-glycyrrhetinic acid derivatives

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays an important role in regulating the cortisol availability to bind to corticosteroid receptors within specific tissue. Recent advances in understanding the molecular mechanisms of metabolic syndrome indicate that elevation of cortisol levels within specific tissues through the action of 11β-HSD1 could contribute to the pathogenesis of this disease. Therefore, selective inhibitors of 11β-HSD1 have been investigated as potential treatments for metabolic diseases, such as diabetes mellitus type 2 or obesity. Here we report the discovery and synthesis of some 18β-glycyrrhetinic acid (18β-GA) derivatives (2–5) and their inhibitory activities against rat hepatic11β-HSD1 and rat renal 11β-HSD2. Once the selectivity over the rat type 2 enzyme was established, these compounds’ ability to inhibit human 11β-HSD1 was also evaluated using both radioimmunoassay (RIA) and homogeneous time resolved fluorescence (HTRF) methods. The 11-modified 18β-GA derivatives 2 and 3 with apparent selectivity for rat 11β-HSD1 showed a high percentage inhibition for human microsomal 11β-HSD1 at 10 μM and exhibited IC₅₀ values of 400 and 1100 nM, respectively. The side chain modified 18β-GA derivatives 4 and 5, although showing selectivity for rat 11β-HSD1 inhibited human microsomal 11β-HSD1 with IC₅₀ values in the low micromolar range.     

Corticosteroid 11 beta-hydroxysteroid dehydrogenase activities in vertebrate liver

In this paper, we examine corticosteroid 11 beta-oxidation and 11-reduction as properties of the microsomal 11 beta-hydroxysteroid dehydrogenase complex in vertebrate livers. No hepatic activity in the oxidative direction (11 beta -dehydrogenase) was found in the frog, toad, mud puppy, shark, and bird livers. In contrast, all mammalian livers had active oxidizing enzymes. Latency, defined as microsome-linked activity released by the detergent Triton DF-18, was a property of 11 beta-dehydrogenase in all mammalian livers. Mammal, bird, and dogfish livers reduced 11-dehydrocorticosteroids (11-reductase), while amphibians and bony fish did not. With the exception of rat liver, latency was a property of all the mammalian liver 11-reductases examined.     

Hepatic 11 beta-hydroxysteroid dehydrogenase 1 involvement in alterations of glucose metabolism produced by acidotic stress in rat

11 beta-hydroxysteroid dehydrogenase (HSDs) enzymes regulate the activity of glucocorticoids in target organs. HSD1, one of the two existing isoforms, locates mainly in CNS, liver and adipose tissue. HSD1 is involved in the pathogenesis of diseases such as obesity, insulin resistance, arterial hypertension and the Metabolic Syndrome. The stress produced by HCl overload triggers metabolic acidosis and increases liver HSD1 activity associated with increased phosphoenolpyruvate carboxykinase, a regulatory enzyme of gluconeogenesis that is activated by glucocorticoids, with increased glycaemia and glycogen breakdown. The aim of this study was to analyze whether the metabolic modifications triggered by HCl stress are due to increased liver HSD1 activity. Glycyrrhetinic acid, a potent HDS inhibitor, was administered subcutaneously (20 mg/ml) to stressed and unstressed four months old maleSprague Dawley rats to investigate changes in liver HSD1, phosphoenolpyruvate carboxykinase (PECPK) and glycogen phosphorylase activities and plasma glucose levels. It was observed that all these parameters increased in stressed animals, but that treatment with glycyrrhetinic acid significantly reduced their levels. In conclusion, our results demonstrate the involvement of HSD1 in stress induced carbohydrate disturbances and could contribute to the impact of HSD1 inhibitors on carbohydrate metabolism and its relevance in the study of Metabolic Syndrome Disorder and non insulin-dependent diabetes mellitus.     

Luteinizing hormone induces expression of 11beta-hydroxysteroid dehydrogenase type 2 in rat Leydig cells

Background  

Leydig cells are the primary source of testosterone in male vertebrates. The biosynthesis of testosterone in Leydig cells is strictly dependent on luteinizing hormone (LH). On the other hand, it can be directly inhibited by excessive glucocorticoid (Corticosterone, CORT, in rats) which is beyond the protective capability of 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) and type 2 (11beta-HSD2; encoded by gene Hsd11b2 in rats) in Leydig cells. Our previous study found that LH increases 11beta-HSD1 expression in rat Leydig cells, but the effect of LH on the expression and activity of 11beta-HSD2 is not investigated yet.     

3 beta-hydroxysteroid isomerase dehydrogenase in guinea-pig kidney: possible involvement in 11-deoxycorticosterone formation in situ

3 beta-Hydroxysteroid isomerase dehydrogenase, capable of acting on C21- and C19-3 beta-hydroxy-5-ene-steroids has been found in guinea-pig kidney at equivalent levels to those in guinea pig testes. Of the 3 beta-hydroxy-5-ene-steroids present in guinea pig serum, 21-hydroxypregnenolone occurs in highest concentration (17 nM) followed by pregnenolone (10 nM), whereas 17 alpha-hydroxy-pregnenolone and dehydroepiandrosterone occur in very low concentrations (less than 0.5 nM). Furthermore, the concentration of 21-hydroxypregnenolone relative to 11-deoxycorticosterone (the mineralocorticoid of the guinea pig), is 10:1 (Nishikawa and Strott, Steroids 41 (1983) 105-120). The apparent Km value for 21-hydroxypregnenolone, for the reaction yielding 11-deoxycorticosterone as catalysed by guinea pig kidney microsomes, was 85 nM and the Vmax 33 pmol/min per mg protein. Pregnenolone was a competitive inhibitor (apparent Ki = 5 microM) in the above reaction. A sex difference in the level of the enzyme in the kidney was found (activity in the female was one-third of that in the male) which may indicate that the enzyme is under partial androgen control. 3 beta-Hydroxysteroid isomerase dehydrogenase activity was also detected in guinea pig liver and again it was lower in the female. Whilst the exact role of 3 beta-hydroxysteroid isomerase dehydrogenase in guinea-pig kidney remains uncertain, the data suggest that it may utilise blood-borne 21-hydroxypregnenolone, the later then playing the role of a prohormone.