COMPARATIVE-STUDY OF ADRENAL PROGESTERONE SECRETION DURING ESTROUS CYCLES OF HAMSTERS AND RATS

Adrenal secretory rates and peripheral plasma levels of progesterone (PROG) were determined during the estrous cycles of hamsters and 4-day cyclic rats. In both species, the PROG concentrations in peripheral plasma were never more than 6% of those observed in adrenal venous plasma. In hamsters, adrenal PROG secretory rates varied from 3.8 .+-. 0.8 ng/min at 0800 h on proestrus (P) to 8.5 .+-. 1 ng/min at 200 h on estrus (E). The rates noted on P were among the lowest observed and were similar to those noted at 0800 h the following morning. In rats, adrenal PROG secretory rates varied from 57 .+-. 9 ng/min at 0800 h on E to 130 .+-. 18 ng/min at 2000 h on P. A significant decline occurred between 2000 h on P and 0800 h the following morning. Rats secreted 3 to 8 times more PROG than did hamsters when the secretory rates are expressed as ng/min per 100 mg adrenal. In hamsters, the data suggest a relative lack of influence of female reproductive hormones on adrenal PROG secretion and in turn the latter may not be involved in reproductive hormonal changes leading to ovulation. In rats, the increased adrenal PROG secretion noted on P may be due to the influence of reproductive hormones on adrenocortical function. This elevated rate may in turn influence the hypothalamo-hypophyseal-ovarian axis.