20α-Hydroxysteroid Dehydrogenase Activity in the Rabbit Ovary

Abstract

A spectrophotometric assay for rabbit ovarian 20α-hydroxysteroid dehydrogenase (20α-OH-SDH) is described. In whole ovaries 20α-OH-SDH activity was found to be high during estrus. Following a 100 IU dose of HCG, 20α-OH-SDH activity in whole ovaries declined to ⅙ estrous levels by Day 3 of pseudopregnancy, but increased progressively, approaching estrous levels between Days 15 and 21 of pseudopregnancy. 20α-OH-SDH activity in separated interstitial tissue increased 3.8-fold from Days 4–20, while the activity in corpora lutea (CL) was low and constant between Days 4 and 11, but rose 4-fold between Days 15 and 20. Direct addition of HCG to the extracts had no effect on 20α-OH-SDH activity, but estriol was found to inhibit the enzyme. In contrast, glucose-6-phosphate dehydrogenase (G-6-PDH) activity in CL declined approximately 40% between Days 4 and 20 of pseudopregnancy. The results indicate that increasing 20α-OH-SDH activity is a specific and sensitive index of luteolysis in the rabbit.