RADIOACTIVE SUBSTRATE DISAPPEARANCE ASSAYS IN STEROID ENZYMOLOGY: THE EFFECTS OF PITUITARY TROPHINS AND OESTRADIOL ON THE FINAL STEPS OF ANDROGEN BIOSYNTHESIS

Abstract

ABSTRACT An assessment of the feasibility and advantages of measurement of substrate disappearance for assays of enzyme activity in steroid metabolism was made, and the method was shown to be of wide applicability when certain conditions are met. The method was tested by application to the final steps of androgen biosynthesis by rat testis microsomes. and it was found that chronic treatment of the animal with large doses of LH prior to isolation of the enzyme preparation decreased the activity in this tissue of progesterone-17-hydroxylase, 17α-hydroxy-20-carbonyl cleavage enzyme and 17β-hydroxysteroid (testosterone) dehydrogenase. Oestradiol administration caused a less marked decrease in hydroxylase and dehydrogenase activity without effect on the cleavage enzyme, while FSH administration did not greatly alter the activity of these three enzymes. Chronic TSH administration gave results similar to those obtained with oestradiol.