Distribution of delta-5 -3beta-hydroxysteroid dehydrogenase activity in the Graafian follicle of the sheep.

The localization of delta-5 -3beta-hydroxysteroid dehydrogenase (3 beta-HSD) has been examined in ovarian follicles in vivo and in vitro, and related to oestrogen and progesterone production. In vivo, during the oestrous cycle, enzyme activity was restricted to the theca interna of the one or two most advanced follicles in each animal, but was present only between Day 2 and 5 and between Day 13 and ovulation. High levels of oestrogen were found in the ovarian venous blood only when follicles containing 3 beta-HSD were present. When sheep were injected with PMSG, the theca interna in a number ofsmall follicles acquired 3 beta-HSD activity and began to secrete oestrogen within 12 hr of the injection. The enzyme was not detected in the membrana granulosa of any follicles before ovulation but within a few hours of ovulation, 3 beta-HSD activity was present in the granulosa lutein cells. In vitro, large activated follicles exhibited 3 beta-HSD activity in the theca interna and secreted high levels of oestrogen into the culture medium. When LH was added to the medium oestrogen secretion was inhibited; within 48 hr, the follicles were secreting high levels of progesterone, and 3 beta-HSD activity was present in both the membrana granulosa and the theca interna. Dibutyryl cyclic adenosine monophosphate mimicked the effect of LH in suppressing oestrogen secretiion, but did not induce production of progesterone; the distribution of 3 beta-HSD activity infollicles treated with this nucleotide was the same as in those cultured in control medium.