Side-chain cleavage of C21 steroids by testicular microsomal cytochrome P-450 (17 alpha-hydroxylase/lyase): involvement of heme

Leptin alters adrenal responsiveness by decreasing expression of ACTH-R, StAR, and P450c21 in hypoxemic fetal sheep

The late gestation increase in adrenal responsiveness to adrenocorticotropin (ACTH) is dependent upon the upregulation of the ACTH receptor (ACTH-R), steroidogenic acute regulatory protein (StAR), and steroidogenic enzymes in the fetal adrenal. Long-term hypoxia decreases the expression of these and adrenal responsiveness to ACTH in vivo. Leptin, an adipocyte-derived hormone which attenuates the peripartum increase in fetal plasma cortisol is elevated in hypoxic fetuses. Therefore, we hypothesized that increases in plasma leptin will inhibit the expression of the ACTH-R, StAR, and steroidogenic enzymes and attenuate adrenal responsiveness in hypoxic fetuses. Spontaneously hypoxemic fetal sheep (132 days of gestation, PO(2) ≈ 15 mm Hg) were infused with recombinant human leptin (n = 8) or saline (n = 7) for 96 hours. An ACTH challenge was performed at 72 hours of infusion to assess adrenal responsiveness. Plasma cortisol and ACTH were measured daily and adrenals were collected after 96 hours infusion for messenger RNA (mRNA) and protein expression measurement. Plasma cortisol concentrations were lower in leptin- compared with saline-infused fetuses (14.8 ± 3.2 vs 42.3 ± 9.6 ng/mL, P < .05), as was the cortisol:ACTH ratio (0.9 ± 0.074 vs 46 ± 1.49, P < .05). Increases in cortisol concentrations were blunted in the leptin-treated group after ACTH(1-24) challenge (F = 12.2, P < .0001). Adrenal ACTH-R, StAR, and P450c21 expression levels were reduced in leptin-treated fetuses (P < .05), whereas the expression of Ob-Ra and Ob-Rb leptin receptor isoforms remained unchanged. Our results indicate that leptin blunts adrenal responsiveness in the late gestation hypoxemic fetus, and this effect appears mediated by decreased adrenal ACTH-R, StAR, and P450c21 expression.

Antagonism of alcohol-induced suppression of rat testosterone secretion by an inhibitor of nitric oxide synthase

To examine whether nitric oxide (NO) mediates the suppression of testosterone secretion by alcohol (ethanol), adult male rats were pretreated with a NO synthase inhibitor, NG-nitro-L-arginine methyl ester (NAME), then treated with alcohol. Serum and testicular interstitial fluid (TIF) testosterone concentrations, serum luteinizing hormone (LH) concentrations, blood alcohol concentrations (BAC), and TIF volumes were measured 2 hr after alcohol treatment at a time of peak effects of alcohol and NAME on testosterone secretion. Pretreatment with NAME (30 or 100 mg/kg, subcutaneous) 30 min before alcohol treatment (0.5-3 g/kg, intraperitoneal) completely blocked the alcohol-induced suppression of testosterone secretion into the general circulation and into TIF without significantly altering blood alcohol concentrations (BAC) or TIF volumes. These results support the hypotheses that NO synthase inhibitors can antagonize alcohol-induced suppression of testicular steroidogenesis, that alcohol interacts with arginine-NO synthase systems that regulate testicular steroidogenesis, and that NO is involved in mediating alcohol's testicular and reproductive effects.

Epitestosterone--a potent competitive inhibitor of C21-steroid side chain cleavage in the testis

Epitestosterone (17 alpha-hydroxy-4-androsten-3-one) inhibits both 17 alpha-hydroxylation and consequent side chain cleavage of the resulting 17 alpha-hydroxyprogesterone in the rat testicular microsomes. The inhibitory activity in terms of the Ki is 2 and 1.5 times as high, respectively, as that of cyproterone acetate.

Nitric oxide control of steroidogenesis: endocrine effects of NG-nitro-L-arginine and comparisons to alcohol

Recent studies suggest that nitric oxide (NO) may regulate hormone biosynthesis and secretion. This was tested by treating male rats with NG-nitro-L-arginine methyl ester (NAME), a NO synthase inhibitor, and measuring serum and testicular interstitial fluid testosterone and serum corticosterone, luteinizing hormone (LH), and prolactin (PRL). The effect of NG-nitro-L-arginine (NA), a less-soluble form of the same NO synthase inhibitor, on the reproductive suppressant actions of alcohol was also examined. NAME increased testosterone and corticosterone secretion dose-dependently without affecting LH and PRL secretion. The alcohol-induced suppression of testosterone or LH secretion was not altered by treatment with NA. Although effects of NAME and NA on other systems may be involved, these results indicate that testicular and adrenal steroidogenesis are negatively regulated by endogenous NO and that NO does not regulate LH and PRL secretion or inhibit the testicular steroidogenic pathway in the same way as alcohol.

Cytochrome P-450 C21scc: one enzyme with two actions: hydroxylase and lyase

Testis, adrenal, ovary and placenta contain a microsomal cytochrome P-450 that is capable of converting progesterone to androstenedione and pregnenolone to dehydroepiandrosterone. This conversion requires 17 alpha-hydroxylation followed by C17,20-lyase activity which are both catalyzed by this one protein. Gene cloning and Northern blotting reveal that, at least in man, the same gene is responsible for both testicular and adrenal enzymes. The enzyme was first purified from neonatal pig testis. Both the testicular and adrenal enzymes show a marked preference for the 5-ene substrate (pregnenolone) in keeping with the extensive use of the 5-ene pathway in that species. Affinity alkylation with 17 alpha-bromoacetoxyprogesterone reveals a conserved cysteine at the active site of the enzyme and confirms the conclusion that a single enzyme catalyzes both reactions. Under some circumstances the enzyme catalyzes only 17 alpha-hydroxylation to permit the formation of the C21 steroid cortisol. The regulation of lyase activity, i.e. the determination of the extent to which the second activity is expressed, results from the availability of P-450 reductase. No doubt the greater concentration of this protein in testicular as opposed to adrenal microsomes (x 3.5) is responsible for the production of androgens in the testis and cortisol in the adrenal. Testicular cytochrome b5 also specifically stimulates lyase activity and also causes the porcine enzyme to catalyze a new reaction, i.e. delta 16-synthetase, resulting in synthesis of the important pheromone androsta-4,16-dien-3-one from progesterone.