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

Abstract

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...