In vitro Steroidogenesis in Corpora Lutea and Nonluteal Ovarian Tissues of the Cyclic Hamster

Abstract

The steroidogenic capacity of the luteal and nonluteal ovarian (NLO) compartments was assessed during the hamster estrous cycle by 2 h in vitro incubations in Kreb’s Ringer bicarbonate. On Day 1 of the estrous cycle (Day I is the day of ovulation), the most striking results obtained from the incubation of NLO and corpora lutea (CL) were the inabilities of these 2 compartments to synthesize significant amounts of progesterone (P) despite serum P levels of 6 ng/ml. In fact, the NLO lost P at a rate of 2.5 ng/mg/h, whereas the CL failed to synthesize significant quantities of P. These results were further substantiated by incubations of intact ovaries (CL + NLO) on Day 1 which revealed a significant net loss of P (0.80 nglmg/h). P levels in NLO (9.0 ng/mg) were higher on Day 1 than on any other day of the cycle and CL on Day 1 contained approximately 14.0 ng P/mg. Also on Day 1, NLO syntheses of androstenedione (A), testosterone (T), estrone (E1) and estradiol (E2) were at baseline levels compared to synthesis on other days of the cycle. The Day 1 results suggest that a major portion of the large quantity of P contained within the ovary prior to incubation was converted to steroids other than those measured. Day 1 CL failed to syn’ thesize significant quantities of P; this poor steroidogenic capability may result from their incomplete luteinization. On Day 2 of the cycle, a significant upswing in production of P and A by NLO and CL was accompanied by increased production rates of E1 and E2 by NLO. However, T production by NLO and CL was unchanged from Day 1. Corpora lutea did not produce estrone or estradiol on any day. Luteal regression which occurred by Day 3 was characterized by a significant decline of P in CL and serum. The production rate of P by CL was also significantly lower on Day 3 than on Day 2. Concomitant with luteal regression was an increase in the production rate of E1 and E, by NLO without changes in NLO production of P and T. These changes were paralleled by increased concentrations of E1 and E2 in serum and NLO. Steroid production on Day 4 was similar to that on Day 3, except that A production was higher on Day 4 than at any other time, however, serum A concentration remained unchanged from Day 3. The results of this study indicate that in vitro, the Day 1 hamster ovary (CL and NLO) exhibits a low level of steroidogenic activity; thereafter, an upswing in steroidogenic activity was observed in both ovarian compartments (CL and NLO) until the demise of the CL on Day 3.