Source of Ovarian Preovulatory Progesterone

AN increase in plasma progesterone has been detected before ovulation in several species. There is, however, no definitive information as to which ovarian compartments produce this progesterone. Previous results with the golden hamster have demonstrated a preovulatory progesterone surge after the critical period for gonadotrophin release on the afternoon of pro-oestrus (day 4)^1,2. This is paralleled by the development of 3β-hydroxysteroid dehydrogenase (3βHSD) activity in the theca interna and granulosa of pre-ovulatory follicles³, suggesting they could be a source of preovulatory progesterone. As the interstitium also contains 3βHSD activity, it could be an additional source of progesterone³. Hamster corpora lutea, however, have negligible 3βHSD activity during pro-oestrus³ and are not capable of producing progesterone when isolated and incubated in vitro (Leavitt et al., unpublished work).