PATHWAYS FOR THE BIOSYNTHESIS OF OESTRADIOL IN THE RABBIT OVARIAN FOLLICLE IN VITRO

Abstract

Laboratoire d'Endocrinologie, Hópital-Notre-Dame et Département de Médecine, Université de Montréal, Montréal, Canada (Received 8 June 1977) In ovarian tissues, the synthesis of oestrogen from pregnenolone can proceed via progesterone and the 3-oxo-4-unsaturated steroid pathway or by way of dehydroisoandrosterone and the 5-unsaturated steroid pathway. In human ovaries, the follicle seems to prefer the 5-unsaturated pathway for formation of oestrogen (Ryan & Petro, 1966), whereas in the corpus luteum, the 4-unsaturated steroid pathway may be the only one that is operative (Ryan, 1963). The situation is not so clear in other species. In the rabbit, a reflex ovulator, ovarian follicles are known to secrete oestradiol (YoungLai, 1972). Furthermore, isolated follicles can form oestradiol, androgens and progesterone from endogenous (Mills, 1975) or exogenous (Mills & Savard, 1972) precursors in vitro. Mills & Savard (1972) incubated rabbit follicles with [1-14C]acetate and isolated labelled oestradiol and intermediates involved in the 4- and 5-unsaturated steroid