Translation of Rat Ovarian mRNA to Two 20α-hydroxysteroid Dehydrogenase Isozymes in Xenopus Oocytes

Abstract

20α-Hydroxysteroid dehydrogenase (20α-HSD) in rat luteal tissue catalyzes the conversion of progesterone into a biologically inactive steroid, 20α-hydroxypregn-4-en-3-one (20α-OHP) and depletes the output of progesterone into the circulation. An increase in 20α-HSD activity in luteal tissue is therefore a prerequisite for the regression of functional corpora lutea in rats. We have reported that ovarian 20α-HSD is composed of two isoforms (HSD1 and HSD2). In this study, among batches of ovaries collected randomly during the estrous cycle, we selected two batches (batches A and B): the cytosol preparation from batch A contained both HSD1 and HSD2 activities, whereas that from batch B contained only HSD1 activity. From these 2 batches, we extracted mRNA, and each mRNA preparation was subjected to translation in Xenopus oocytes. The translation products of batch A exhibited both HSD1 and HSD2 activities, and those of batch B only HSD1 activity in accordance with the enzymatic activities observed in the respective cytosolic preparations. The results are compatible with the presence of two distinct mRNAs coding HSD1 and HSD2, and if so their transcription will be regulated separately according to the functional state of the ovary.