Induction of human endometrial estradiol dehydrogenase by progestins.

Estradiol-17beta dehydrogenase activity in proliferative human endometrium (average of 1.5 nmole of estrone formed from estradiol/mg protein/h) was stimulated as much as as 6-fold during incubations of tissue slices in culture medium containing progesterone. Stimulation was already detectable at 7 h and the highest activity values were reached at 48-72 h of incubation in the presence of excess progesterone. Maximal stimulation was achieved with concentrations of the hormone of 0.25 mug/ml or higher. At concentrations approximately equal to midluteal plasma levels (20 ng/ml) more than 50% of the maximal response was observed. Norgestrel (17alpha-ethynyl-18-methyl-19-nortestosterone) was also effective in inducing enzymatic activity. The similarity of the effects obtained with progesterone (a possible substrate for estradiol dehydrogenase) and the synthetic progestin indicates that the stimulation of enzymatic activity was not due to substrate induction. Addition of estradiol to the culture medium had no influence on the activity of the enzyme. The induction of estradiol dehydrogenase by progesterone was inhibited by puromycin or actinomycin D. These observations indicate that progestational agents increase the rate of de novo synthesis of the enzyme. Stimulation of endometrial estradiol dehydrogenase was also observed after 2-3 day oral administration of medroxyprogesterone acetate to women in the follicular phase. In contrast, the enzymatic activity in endometrium obtained from women taking estrogens was found to be as low as in normal proliferative tissue. These in vitro and in vivo results point to progesterone as the agent responsible for the 10-fold increase in endometrial estradiol dehydrogenase activity observed during the luteal phase in menstruating women. Data obtained from superfusion studies of estrogen dynamics in endometrium indicate that changes in enzyme concentrations may play a physiologic role in the regulation of tissue levels of estradiol.     

Studies on the human testis. VI. NADH-linked reactions of microsomal steroid 20alpha-and 20beta-hydroxysteroid dehydrogenase and 17alpha-hydroxylase.

NADH-linked 20alpha- and 20beta-hydroxysteroid dehydrogenase and 17alpha-hydroxylase activities were demonstrated in the microsomal fraction of the human testis. The microsomal 20alpha-hydroxysteroid dehydrogenase showed substrate affinity to pregnenolone and progesterone and not to 17alpha-hydroxyprogesterone and preferred NADH to NADPH as a hydrogen donor. In the presence of NADH, the optimal pH for the enzyme was 7.7 and the apparent Michaelis constants of the enzyme for progesterone and pregnenolone at 37 C and pH 7.4 were 6.9-7.1 X 10-6M and in the order of 10-5M, respectively, 17alpha, 20beta-Dihydroxypregn-4-en-3-one was the only significant metabolite produced from 17alpha-hydroxyprogesterone by microsomal fraction of the human testis in the presence of NADH. The apparent Michaelis constant of microsomal 20beta-hydroxysteroid dehydrogenase for 17alpha-hydroxyprogesterone in the presence of NADH was in the order of 10-5M at 37 C and pH 7.4. The microsomal 17alpha-hydroxylase catalyzed the metabolism of pregnenolone and progesterone at a similar rate in the presence of NADH. The optimal pH and the apparent Michaelis constant at 37 C and pH 7.4 of the NADH-linked reaction of 17alpha-hydroxylase for progesterone were 7.7 and 5.3-5.4 X 10-7M, resepctively. The NADH-linked enzyme activity for progesterone was competitively inhibited by both pregn-5-ene-3beta, 20alpha-diol (inhibition constant: 1.7 X 10-7M) and 20alpha-hydroxypregn-4-en-3 one (inhibition constant: 6.6 X 10-7M), and was resistant to poor oxygen supply during incubation. The results indicate that the microsomal 20alpha-hydroxysteroid dehydrogenase is a different enzyme from the one in the soluble fraction of the human testis and that microsomal 17alpha-hydroxylase in the human testis is activated by NADH as well as NADPH.     

Progesterone metabolism in the human kidney and inhibition of 11beta-hydroxysteroid dehydrogenase type 2 by progesterone and its metabolites

Progesterone binds with high affinity to the mineralocorticoid (MC) receptor, but confers only very low agonistic MC activity. Therefore, progesterone is a potent MC antagonist in vitro. Although progesterone reaches up to 100 times higher plasma levels in late pregnancy than aldosterone, the in vivo MC antagonistic effect of progesterone seems to be relatively weak. One explanation for this phenomenon could be local metabolism of progesterone in the human kidney, similar to the inactivation of cortisol to cortisone by the 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2. We studied the metabolism of progesterone in the human kidney in vitro and found reduction to 20alpha-dihydro (DH)-progesterone as the main metabolite. Ring-A reduction to 5alpha-DH-progesterone, 20alpha-DH-5alpha-DH-progesterone, and 3beta,5alpha-tetrahydro (TH)-progesterone was also documented. We further showed for the first time that 17-hydroxylation of progesterone (17alpha-OH-progesterone, 17alpha-OH, 20alpha-DH-progesterone), normally localized in the adrenals and the gonads, occurs in the human adult kidney. We found no formation of deoxycorticosterone from progesterone in the human adult kidney. Using human kidney cortex microsomes, we tested the inhibitory potency of progesterone and its metabolites on the 11beta-HSD type 2. The most potent inhibitor was progesterone itself (IC50 = 4.8 x 10(-8) mol/L), followed by 5alpha-DH-progesterone (IC50 = 2.4 x 10(-7) mol/L), 20alpha-DH-progesterone, 3beta,5alpha-TH-progesterone, 17alpha-OH-progesterone, and 20alpha-DH-5alpha-DH-progesterone (IC50 between 7.7 x 10(-7) mol/L and 1.3 x 10(-6) mol/L). The least potent inhibitor was 17alpha-OH,20alpha-DH-progesterone. In addition to progesterone metabolism by the kidney, the inhibition of 11beta-HSD type 2 by progesterone and its metabolites could be a second explanation for the weak MC-antagonist activity of progesterone in vivo. Inhibition of 11beta-HSD type 2 leads to an increase of intracellular cortisol in a way that the local equilibrium between the MC agonist cortisol and the antagonist progesterone is shifted to the agonist side.     

Studies on the activities of steroidogenic enzymes in corpora lutea of early pregnant rats treated with abortifacient drugs (author's transl)]

The major role of the corpus luteum is biosynthesis of progesterone. Luteal function has been investigated by following plasma progesterone concentrations and by studying ultrastructural and histochemical changes in corpora lutea. Recently, changes in enzyme activities concerned with formation and degradation of progesterone are taken into investigation in order to understand the regulation of luteal function. In rat ovaries, progestational potency of ovarian secretions has been regulated by the activity of 20 alpha-hydroxysteroid dehydrgoenase (20 alpha-HSD), Which catabolizes progesterone to 20 alpha-hydroxypregn-4-en-3-one, progestatinally inert steroid. In regressing corpora lutea, extensive conversion of progesterone to 20 alpha-hydroxypregn-4-en-3-one occurred with a marked increase in 20 alpha-HSD activity as well as a decrease in plasma progesterone concentrations. On the other hand, histochemical studies of glucose-6-phosphate dehydrogenase (G 6 PDH) and delta5-3beta-hydroxysteroid dehydrogenase (3 beta-HSD) have been investigated without any remarkable changes in corporalutea at their early stages of luteolysis. In the present study the activities of steroidogenic enzymes in corpora lutea of pregnant rats are measured after treatment with a variety of abortifacient drugs, and compared with those in corpora lutea of 1 day post partum rats which showed changes characteristic of spontaneous luteolysis. On days 7 to 9 of pregnancy, Wistar-strain pregnant rats were injected with either prostaglandin F2alpha (PGF2alpha), aminoglutethimide or clomiphene citrate (clomid). Animals were sacrificed 15 to 63 hrs. after the last injection, and implantation sites were inspected. Ovaries were removed, and corpora lutea dissected free, weighed and homogenized. The homogenate was centrifuged at 105,000g for 60 min. The supernatant solution was assayed for the activities of G 6 PDH, 6-phosphogluconate dehydrogenase (6 PGDH), malic enzyme, ATP citrate lysase, 20 alpha-HSD and pyruvate kinase. The pellet fraction was re-homogenized, and centrifugated 2,000 g for 5 min. The supernatant solution was used for the assay of 3 beta-HSD. Complete fetal resorption was observed in all rats treated with PGF2alpha, while 7 out of 15 rats (47%) treated with both PGF2alpha and LH-RH maintained pregnancy. In intact rats after treatment with both drugs, lutein cells showed ultrastructures characteristic for luteolysis, although the degree of luteolysis was greatly diminished compared with PGF2alpha-treated ones. In agreement with these ultrastructural findings, 20alpha-HSD activity in corpora lutea was maintained at a rather low level in intact rats, while it was increased moderately in aborted ones after treatment with both drugs. In PGF2alpha-treated rats, G 6 PDH activity increased to 140% and malic enzyme activity decreased to 27% of the activity in control rats. In aminoglutethimide-treated rats, the activites of G 6 PDH and malic enzyme were decreased, while 2-alpha-HSD activity was maintained at a low level...     

Change of steroidogenic pathways in the ovary of a tropical catfish, Clarias macrocephalus, Gunther, after hCG treatment

Adult female catfish received an im injection of 454 IU hCG in 0.2 ml saline. Sixteen hours later, the ovarian tissue from the hCG-treated or control fish was aerobically incubated in vitro with 4-[14C]progesterone or 17 alpha-hydroxyprogesterone at 30 degrees for 60 min. When progesterone was employed as the substrate, significant production of androstenedione and testosterone was observed in the control group. However, after the hCG injection, a markedly higher amount of 20 beta-hydroxy-4-pregnen-3-one was produced. Furthermore, the androgen production was diminished, and the production of 5 beta-reduced C21 metabolites such as 5 beta-pregnane-3,20-dione and 3 alpha-hydroxy-5 beta-pregnan-20-one was also reduced in the hCG-treated group. From 17 alpha-hydroxyprogesterone as a substrate, considerable amounts of androstenedione and testosterone were obtained as the metabolites in the control group. However, after the hCG treatment, production of 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-diOHprog) and its 5 beta-reduced metabolite was markedly stimulated, while the androgen production was reduced drastically. By evaluating the yield of each product, it was suggested that the tentatively calculated activity of 17 alpha-hydroxylase and C-17-C-20 lyase was diminished by the hCG treatment and that 20 beta-hydroxysteroid dehydrogenase was activated. It indicates that hCG changed the ovarian steroidogenic pathway from androgen production to formation of 17 alpha, 20 beta-diOHprog, an inducer of germinal vesicle breakdown.     

Deoxycorticosterone biosynthesis in human kidney: potential for formation of a potent mineralocorticosteroid in its site of action.

The extra-adrenal formation of deoxycorticosterone (DOC) from plasma progesterone has been demonstrated in humans. In those studies it was shown that in some persons the volume of plasma cleared of progesterone by DOC formation was great, namely, 75 liter/24 hr. Because steroid 231-hydroxylase activity [steroid 21-monooxygenase; steroid, hydrogen-donor:oxygen oxidoreductase (21-hydroxylating), EC 1.14.99.10] could not be demonstrated in homogenates or microsome-enriched preparations of human lung or liver tissue, we speculated that the 21-hydroxylation of plasma progesterone might take place in the kidney. Employing whole tissue homogenates and microsome-enriched preparations of human kidney tissue, we demonstrated the formation of [3H]DOC from kidney tissue, we demonstrated the formation of [3H]DOC from [3H]progesterone. The rate of formation of DOC from progesterone in microsomal preparations from kidney tissues of adult humans varied from 0 to 803 pmol per mg of microsomal protein per hr. The value computed for the apparent Km of the enzyme for progesterone was 0.140 microM. On the basis of these findings, we conclude that steroid 21-hydroxylase activity is present in human kidney tissue and that the kidney may be an important site of DOC formation as well as a site of DOC action.     

Effect of androgen and estrogen treatment on hamster liver and kidney estrogen 2-/4-hydroxylase activity

The activity of microsomal estrogen 2-/4-hydroxylase enzyme (ESH), which mediates the formation of catechol estrogens, was determined in the hamster kidney and liver under different endocrine states and after treatment with diethylstilbestrol (DES) and 5 alpha-dihydrotestosterone alone or in combination. Our results indicate that at least 64% of the renal ESH activity is localized in the kidney cortex. Employing either estrone or 17 beta-estradiol as substrate, a significant decline in renal ESH activity was observed after castration, with estrone remaining the more active substrate. In contrast, hepatic ESH activity, which is about 2.0- to 2.5-fold higher than the kidney enzyme, was not altered after gonadectomy using either estrogen substrate. A further reduction in renal ESH activity was found in DES-treated castrated hamsters when estrone was used. Androgen treatment resulted in a nearly 2-fold increase in kidney ESH activity using either estrogen substrate. Animals treated concomitantly with DES and 5 alpha-dihydrotestosterone exhibited catechol estrogen formation similar to untreated castrate hamster kidney microsomes. In contrast, hamster liver ESH activity was unaffected by androgen treatment. HPLC profiles of the catechol estrogen monomethyl ethers confirm these changes. Hamster kidney ESH activity in females was only 5-7% of that in intact males. Ovariectomy resulted in a 3-fold increase in the activity of this microsomal enzyme with either estrogen substrate. ESH activity was substantially increased in uteri of intact animals after androgen treatment. These data clearly demonstrate that ESH activity is under androgen control, particularly in the hamster kidney of both sexes, and may be pertinent in understanding the antagonism of this hormone in estrogen-induced renal tumorigenesis.     

Two Brothers with Skewed Thiopurine Metabolism in Ulcerative Colitis Treated Successfully with Allopurinol and Mercaptopurine Dose Reduction

Thiopurine therapy effectively maintains remission in inflammatory bowel disease. However, many patients are unable to achieve optimum benefits from azathioprine or 6-mercaptopurine because of undesirable metabolism related to high thiopurine methyltransferase (TPMT) activity characterized by hepatic transaminitis secondary to increased 6-methylmercaptopurine (6-MMP) production and reduced levels of therapeutic 6-thioguanine nucleotide (6-TGN). Allopurinol can optimize this skewed metabolism. We discuss two brothers who were both diagnosed with ulcerative colitis (UC). Their disease remained active despite oral and topical mesalamines. Steroids followed by 6-mercaptopurine (MP) were unsuccessfully introduced for both patients and both were found to have high 6-MMP and low 6-TGN levels, despite normal TMPT enzyme activity, accompanied by transaminitis. Allopurinol was introduced in combination with MP dose reduction. For both brothers addition of allopurinol was associated with successful remission and optimized MP metabolites. These siblings with active UC illustrate that skewed thiopurine metabolism may occur despite normal TPMT enzyme activity and can lead to adverse events in the absence of disease control. We confirm previous data showing that addition of allopurinol can reverse this skewed metabolism, and reduce both hepatotoxicity and disease activity, but we now also introduce the concept of a family history of preferential MP metabolism as a clue to effective management for other family members.     

Studies on hepatic glucose cycles in normal and methylprednisolone-treated dogs

In unanesthetized normal and methyl-prednisolone (MP)-treated dogs the rate of appearance of glucose was measured simultaneously with 2-³H (RA₂ = hepatic glucose output), 6-³H (Ra₆ = hepatic glucose production), and ¹⁴C-glucose (U) (RaC) as tracers (primed constant rate infusion). The substrate (“futile”) cycle of glucose (SC: gl ? gl-6-P) was obtained from Ra₂ - Ra₆, and Ra₆ - RaC gave the recycling (RC) of radiocarbons. In normal dogs SC and RC represented 13% and 11% of Ra₆, respectively. MP increased SC almost eightfold without altering RC. Infusion of glucagon (increased breakdown of glycogen, inhibition of glycogen synthetase) or mannoheptulose (inhibition of glucokinase) as well as exercise increased SC. MP greatly potentiated the effect causing SC to rise to 20 times the normal base-line. In both groups there was a direct correlation between Ra₆ and SC. Glucose infusion did not alter SC in the controls, but increased it in the MP-treated dogs by suppressing Ra₆ more than Ra₂. It is suggested that the multifunctional character of gl-6-Pase is at least partly responsible for the glucose substrate cycle, using gl-6-P as one of the phosphate donors: gl-6-P + ³H-gl ? ³H-gl-6-P+gl. The activity of this enzyme is greatly elevated by the glucocorticoid, and it can be further enhanced by increasing the availability of gl-6-P by raising Ra₆.     

G6PD Hillbrow: A New Variant of Glucose-6-Phosphate Dehydrogenase Associated with Drug-induced Haemolytic Anaemia

A new genetic variant of the red cell enzyme glucose-6-phosphate dehydrogenase is described. It was observed in a patient presenting with severe haemolytic anaemia and renal failure following ingestion of an overdose of Beserol (paracetamol and chlormezanone). The enzyme in the red cell had 12% of the activity of a normal B+ control, but only slightly lower activity in the kidney compared with a normal control. The red cell enzyme showed normal electrophoretic mobility and thermostability, a biphasic pH optimum curve, higher than normal utilization of the substrate analogues 2-deoxy-glucose-6-phosphate and deamino-NADP, and lower than normal Michaelis constants for both substrates, glucose-6-phosphate and NADP. The enzyme was strongly inhibited in vitro by high concentrations of paracetamol and chlormezanone. The extent of inhibition was similar to that for the enzyme from a normal B+ individual.     

Inhibition of S6 kinase by rapamycin blocks maturation of Rana dybowskii oocytes

Studies were carried out to define the hormone-induced signal transduction pathway during maturation of Rana dybowskii oocytes. Rapamycin, a specific inhibitor of S6 kinase, blocked progesterone-induced oocyte germinal vesicle breakdown (GVBD) in a dose-dependent manner indicating that S6 kinase is required for meiotic maturation of Rana oocytes. Addition of rapamycin within 3 h, but not 6 h, of progesterone treatment inhibited GVBD. In contrast, cycloheximide, a general protein synthesis inhibitor, blocked GVBD even when added 9 h after progesterone addition. A twofold increase in S6 kinase activity occurred within 1 h of progesterone stimulation and rapamycin inhibited this activity. Rapamycin also suppressed, in a dose-dependent manner, progesterone-induced protein synthesis during the first 12 h of culture but less effectively later. Histone H1 kinase activity (maturation-promoting factor, MPF) was observed in oocyte extracts at two different times (between 6 and 9 h and at 24 h) following progesterone stimulation. Rapamycin blocked H1 kinase activity between 6 and 9 h of culture but not that observed at 24 h. In contrast, cycloheximide suppressed progesterone-induced H1 kinase activity as well as protein synthesis throughout the course of incubation. Such results indicate that rapamycin and cycloheximide have common and unique effects on oocyte maturation and suggest that progesterone-induced S6 kinase activity is closely associated with induction of protein synthesis and activation of MPF during oocyte maturation. Results in Rana contrast with those obtained in Xenopus where rapamycin inhibited S6 kinase but failed to inhibit GVBD or protein synthesis. Differences in the response of Rana and Xenopus oocytes to rapamycin are discussed in relation to seasonal, biochemical, and species variations.     

Kinetic studies on ovarian C-17,20-lyase activity: effect of luteinizing hormone surge

It has been shown that 3 h after the preovulatory gonadotropin surge, an abrupt decrease occurs in follicular C-17,20-lyase (lyase) activity which causes a decrease in C19-steroid production. To determine the reason for the reduced lyase activity, we used rats that were induced to ovulate by means of PMSG administration. In these rats, a 54% decrease in lyase activity occurred at the peak of the LH surge. When the gonadotropin surge and ovulation were blocked by pentobarbitone the decrease was prevented. Administration of LH to the pentobarbitone-blocked rats reduced lyase activity to well below the level reached after the endogenous gonadotropin surge. In cycling proestrous rats as well, human CG (hCG) decreased the lyase activity, as measured in isolated follicles 3 h after hCG administration. Out of three potential inhibitory steroids for lyase activity; progesterone, 3 alpha,17 alpha-dihydroxy-5 alpha-pregnen-20-one, and 17 alpha,20 alpha-dihydroxy-4-pregnen-3-one, only the last compound inhibited competitively ovarian lyase activity. The inhibition constant (Ki) value was 29 microM. In order to explore which of the two activities of the lyase complex is regulated by the gonadotropin, a double label double substrate experiment was conducted using [14C]progesterone with [3H]17 alpha-hydroxyprogesterone (17 alpha-OHP). With this assay procedure, we could determine in the same experiment the site of stimulation, the preferred substrate, and the amount of conversion. The conversion of progesterone to 17 alpha-OHP, as well as the conversion to androstenedione were significantly inhibited throughout the reaction by the gonadotropin. Thus, the changes in ovarian lyase after hCG mimic those of 17 alpha-hydroxylase. The labeling pattern of androstenedione showed that the ovarian lyase complex catalyzed the conversion preferentially from progesterone. Whereas the 3H/14C ratio in androstenedione varied between 0.29 to 0.76, the ratios in the 17 alpha-OHP were from 5 to 22. Thus, the exogenous 17 alpha-OHP did not equilibrate with the product formed from progesterone. The effect of the hCG was to decrease the preference of progesterone over 17 alpha-OHP as substrate. It is concluded that: the LH of the surge inhibits both the 17 alpha-hydroxylase and lyase activities. The ovarian lyase complex shows a preference for progesterone as a substrate rather than 17 alpha-OHP. 17 alpha-OHP is not an obligatory intermediate in androstenedione production in ovarian tissue. hCG affects the ovarian lyase complex by shifting the relative preference of substrates towards 17 alpha-OHP.     

The cytochrome P450(17) alpha (17 alpha-hydroxylase/C17,20-lyase) activity of the junctional zone of the rat placenta

The cytochrome P450 responsible for androgen synthesis by the placenta during the second half of pregnancy in the rat was studied in intact and hypophysectomized animals. The two activities of P450(17) alpha, 17 alpha-hydroxylase and C17,20-lyase, were limited to the junctional zone. C17,20-Lyase activity was greater with progesterone than with 17-hydroxyprogesterone as substrate. Although the apparent Michaelis constants were similar, progesterone had a higher maximum velocity than 17-hydroxyprogesterone. Regardless of substrate, C17,20-lyase activity was greater with NADPH than with NADH as an electron donor, and there was no additive effect using both cofactors. Administration of human chorionic gonadotrophin (hCG; 10 IU at 09.00 and 21.00 h on days 13 and 14 and at 09.00 h on day 15) to intact females resulted in more than a 50% reduction of enzyme activity when measured on day 15. The same dose of hCG given to hypophysectomized animals with delayed implantation, i.e. pituitary removal on day 3 and implantation induced by oestrone 5 days later, had no effect on placental enzyme activity, but increased that in the ovary. Administration of ovine LH by osmotic minipump (days 11-15) to intact females resulted in abortion in all animals. The same treatment to animals hypophysectomized on day 11 produced abortion in three of four rats; enzyme activity was greatly reduced in the single animal with placentas. In contrast, infusion of LH into hypophysectomized animals with delayed implantation increased placental enzyme activities.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro induction of Xenopus oocyte maturation by 4-pregnene-17 alpha, 20 beta-diol-3-one

Maturation in Xenopus oocyte is initiated by progesterone and other steroids. The possibility that a metabolite of progesterone is the active agent was explored. In the present study the 20 beta-dihydro metabolite of progesterone, 4-pregnene-17 alpha, 20 beta-diol-3-one was found to be as potent as progesterone at concentrations of 0.5 to 3.0 microM in inducing germinal vesicle breakdown (GVBD) in Xenopus oocytes. The order of relative potencies of the steroids tested were progesterone approximately equal to 17 alpha-hydroxy-20 beta-dihydroprogesterone greater than 17 alpha-hydroxy-20 alpha-dihydroprogesterone greater than 17 alpha-hydroxyprogesterone greater than 11-deoxycorticosterone. 17 alpha-hydroxy-20 beta-dihydroprogesterone induces the production of maturation-promoting factor leading to GVBD. The 20 beta-dihydro metabolite may be the active metabolite under in vivo condition.     

Progesterone metabolism in human leukemic monoblast U937 cells

Progesterone markedly inhibits the functions of human macrophages and T lymphocytes, and acts as an immunosuppressant during pregnancy. It is important to examine progesterone metabolites to understand the overall bioactive properties of this sex steroid. However, progesterone metabolism has not been examined in human immune cells. The human leukemic monoblast U937 cell line exhibits monocytic lineage and provides a valuable model to analyze monocyte-macrophage differentiation. Therefore, in this study, we analyzed progesterone metabolism in U937 cells by thin-layer chromatography. Progesterone was metabolized to 5alpha-pregnan-3beta,6alpha-diol-20-one via 5alpha-dihydroprogesterone and 5alpha-pregnan-3beta-ol-20-one, and 5alpha-pregnan-3beta,20alpha-diol was also detected as a final metabolic product via 20alpha-dihydroprogesterone and 5alpha-pregnan-20alpha-ol-3-one. 5alpha-reduction (5alpha-reductase type 1) and 20alpha-reduction were involved in the first step of metabolism. To identify the enzyme responsible for the 20alpha-reduction, we screened an U937 cDNA library, and obtained a clone (1.2 kb), which was identical to the human hepatic bile acid-binding protein or 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD). 293 cells transfected with this cDNA demonstrated marked 20alpha-reduction of progesterone to 20alphaDHP, but 20alpha-oxidative, 3alpha-HSD or 17beta-HSD activity was found to be negligible. In experimental animals, the importance of 20alpha-HSD has been reported to be involved in the protection of immune cells from the toxic effects of progesterone. Therefore, our present data suggest that 20alpha-HSD plays an important role in the regulation of progesterone actions in human immune cells.     

Interrenal steroid 21-hydroxylase in eels: primary structure, progesterone-specific activity and enhanced expression by ACTH

Cytochrome P450 21-hydroxylase (P450c21) is a key enzyme for corticosteroidogenesis. To understand the regulatory mechanisms of cortisol production in fish, we have cloned a cDNA encoding P450c21, for the first time in non-mammalian vertebrates, from the head kidney of the eel (Anguilla japonica). The overall similarity of the deduced P450c21 sequence was modest (41-44% amino acid identity) between the eel and mammals. However, the functional domains for steroid-binding, heme-binding and proton-transfer sites were well conserved (74-100% identity). The eel P450c21 mRNA was expressed abundantly in the anterior quarter of the head kidney, but was undetectable in the remaining three-quarters or in other tissues including the gill, heart, liver, intestine, kidney, immature gonad and skeletal muscle. Functional expression of the cDNA clone in non-steroidogenic COS-1 cells produced a protein with high 21-hydroxylase activity to convert progesterone to 11-deoxycortisterone but not 17alpha-hydroxyprogesterone to 11-deoxycortisol, although the latter is a preferred substrate for mammalian P450c21. To examine whether 21-hydroxylated progesterone is actually 17alpha-hydroxylated in the eel interrenal, 11-deoxycorticosterone and (3)H-corticosterone were respectively incubated with the interrenal-containing anterior quarter of the head kidney. The separation of the steroids produced by two HPLC systems revealed that cortisol was produced from both substrates, showing the 17alpha-hydroxylation of 11-deoxycorticosterone and corticosterone in the eel interrenal. ACTH infused at 3 pmol/kg per min for 5 h consistently increased plasma cortisol levels and interrenal P450c21 mRNA levels in seawater eels. These results showed that the interrenal-specific eel P450c21 cloned in this study is involved in cortisol production through conversion of progesterone to 11-deoxycorticosterone in the interrenal-containing anterior quarter of eel head kidney. Furthermore, ACTH stimulates cortisol production in part through enhanced P450c21 expression in the eel interrenal.     

Synovial fluid ATP: a potential substrate for the production of inorganic pyrophosphate.

The enzyme nucleoside triphosphate pyrophosphohydrolase (NTPPPH) is present in all joint fluids and on intraarticular cells. It generates inorganic pyrophosphate (PPi) from nucleoside triphosphate substrate, thus serving as a potential source of the PPi which forms in the cartilages of patients with calcium pyrophosphate dihydrate (CPPD) crystal deposition. NTPPPH is also important in matrix vesicle induced calcification with basic calcium phosphate (BCP) crystals. An articular substrate for this enzyme was sought. ATP was measured in the joint fluids from 107 patients with various forms of arthritis. Synovial fluid ATP levels were higher in patients with CPPD deposits than in osteoarthritis (p less than 0.02) or rheumatoid arthritis (p less than 0.002). ATP also correlated with PPi concentration (p less than 0.05) and with the presence of BCP crystals (p less than 0.05), but not with cellularity of the fluid, NTPPPH activity, or age of the donor. This substrate for NTPPPH may contribute to CPPD crystal deposition by generating PPi and may stimulate matrix vesicle induced formation of BCP crystals in several forms of arthritis.     

Regulation of 11beta-hydroxysteroid dehydrogenase enzymes by dietary sodium in the rat

11Beta-hydroxysterold dehydrogenase enzymes (11beta-HSD1, 11beta-HSD2) regulate access of adrenocorticosteroids to receptors. 11Beta-HSD2 is a dehydrogenase that protects mineralocorticoid receptors from circulating glucocorticoid hormones, 11beta-HSD1 is a reductase that promotes formation of active hormone in glucocorticoid-sensitive tissues. Here we investigate whether low or high sodium diets affect 11beta-HSD enzyme activities and mRNA expression in liver and kidney tissues. 11Beta-HSD activity was measured as dehydrogenation of 3H-corticosterone by microsomes in the presence of NAD or NADP. In situ hybridisation techniques were used to assess expression of 11beta-HSD1 mRNA (liver and kidney) and 11beta-HSD2 mRNA (kidney). Dietary sodium did not affect 11beta-HSD2 mRNA expression in collecting tubules of the medulla: 11beta-HSD1 mRNA in proximal tubules of the inner cortex/outer medulla was lower after a high sodium diet. 11Beta-HSD1 mRNA in liver was unaffected by treatment. Renal enzyme activity with NAD (11beta-HSD2 cofactor) was lower following a high sodium diet (P < 0.05). In the presence of NADP (11beta-HSD1 co-factor), neither renal nor hepatic activities were affected. Dietary sodium restriction appears to increase 11beta-HSD activity by a non-genomic mechanism; this should enhance aldosterone specificity for mineralocorticoid receptors. 11Beta-HSD1 mRNA expression varies independent of enzyme activity and is not clearly related to altered glucocorticoid activity.     

Determinants of angiotensin II generation during converting enzyme inhibition

The reaction of the renin-angiotensin system to acute angiotensin converting enzyme inhibition was investigated in a single-blind, crossover study in nine normal volunteers receiving two out of three regimens in random order: the new converting enzyme inhibitor benazepril (20 mg once or 5 mg four times at 6-hour intervals) or enalapril (20 mg). Plasma converting enzyme activity, drug levels, angiotensin I and angiotensin II, active renin, and aldosterone were measured before and 1-4 hours and 14-30 hours after drug intake. Baseline in vitro plasma converting enzyme activity was 97 +/- 15 nmol/ml/min (mean +/- SD) when Hip-Gly-Gly was used as substrate, but with carbobenzoxy-Phe-His-Leu (Z-Phe-His-Leu) or angiotensin I as substrate it was only 20 +/- 4 and 1.7 +/- 0.3 nmol/ml/min, respectively. Discriminating power at peak converting enzyme inhibition was enhanced with the two latter substrates. In vivo converting enzyme activity was estimated by the plasma angiotensin II/angiotensin I ratio, which correlated well with in vitro converting enzyme activity using Z-Phe-His-Leu as substrate (r = 0.76, n = 252). Angiotensin II levels returned to baseline less than 24 hours after drug administration, whereas in vitro and in vivo converting enzyme activity remained considerably inhibited and active renin together with angiotensin I levels were still elevated. A close linear relation was found between plasma angiotensin II and the angiotensin I/drug level ratio (r = 0.91 for benazeprilat and r = 0.88 for enalaprilat, p less than 0.001). Thus, plasma angiotensin II truly reflects the resetting of the renin-angiotensin system at any degree of converting enzyme inhibition. The ratio of plasma angiotensin II to angiotensin I represents converting enzyme inhibition more accurately than in vitro assays, which vary considerably depending on substrates and assay conditions used.