Steroidogenic potential of the ovary, placenta and blood of the rock hyrax (procavia capensis)

Abstract

Circulating progesterone, Sα-dihydroprogesterone and oestradiol-17β concentrations, and the biosynthetic potential of blood, ovaries and placenta incubated with pregnenolone and progesterone in the absence and presence of β-NADPH, enzyme inhibitors and at various incubation times, was determined for pregnant and non-pregnant hyraxes. Plasma concentrations of 5α dihydroprogesterone were higher than those of progesterone and appear to be metabolically derived from progesterone in the blood of female hyraxes. Plasma concentrations of oestradiol- l7β were low. White blood cells metabolised pregnenolone and progesterone, and whole blood, red blood cells and a mixture of red and white blood cells metabolised only progesterone. Plasma had no biosynthetic potential. All conversions in the blood resulted in the production of compounds A and B, partially identified as 5α- and 5β-reduced metabolites of progesterone. Progesterone metabolism was highest in pregnant animals and the formation of conversion products was lowest during latepregnancy. White blood cells displayed the highest steroidogenic activity, which may be inhibited or negligible in blood. Whole blood had the lowest biosynthetic potential and this may be due to the presence of enzyme inhibitors or progesterone binding proteins in the plasma. Luteal, ovarian residual and placental tissues metabolised both pregnenolone and progesterone. Compound E, formed by luteal tissue, has been identified as 17α-hydroxyprogesterone and compound F, formed by ovarian residual tissue, has been partially identified as 17α-hydroxyprogesterone. Compound H was formed by placental tissue and has been partially identified as 20a-dihydroprogesterone. Luteal tissue may be important for the production and secretion of progesterone into the circulation. Pregnenolone metabolism increased in the presence of B-NADPH as well as with a longer incubation time, and was inhibited by NaF-HgCl.