Follicular steroid content and oocyte meiotic status after PMSG stimulation of immature hamsters

Abstract

Follicular growth was stimulated by the PMSG [pregnant mare serum gonadotropin] administration to immature female hamsters. Changes in the number and size of follicles, their content of progesterone, testosterone, estradiol and estrone (determined in whole follicular homogenates) and the meiotic status of the oocytes were followed for 4 days to monitor follicular development and aging. The results showed that 92% of small antral follicles (371-590 .mu.m) were seen 24-30 h after PMSG stimulation and that the maximum number of medium- (591-740 .mu.m) and large- (> 740 .mu.m) sized antral follicles occurred > 48 h later. There was a progressive increase in the concentrations of testosterone, estradiol and estrone over the first 48-54 h, but maximal values of estrone (geometric mean (limits of 1 SD): 326.5 (230.4-462.7) pg/follicle) lagged 24 h behind the highest values for testosterone (352.5 (242.0-456.0) pg/follicle) and estradiol (718.4 (315.7-1634.7) pg/follicle). The progesterone content of all follicles did not change significantly during the first 72-78 h (range of geometric mean values: 0.25-1.06 ng/follicle), but at 96-102 h, 2 populations of medium- and large-sized follicles could be distinguished on the basis of a low progesterone concentration and this grouping corresponded to the peripheral plasma progesterone values of the animals. Differences in concentrations of testosterone, estradiol and estrone were not found in these 2 groupings at 96-102 h, but large antral follicles contained more estrone (.times. 1.5) than medium-sized follicles. Oocytes recovered from follicles up to 78 h after PMSG stimulation showed few signs of atresia (> 80% viable) and had not resumed meiosis (> 93% had a visible germinal vesicle). At 96-102 h, oocytes from medium and large follicles with a low progesterone content maintained their viability (> 88%), but 41% of oocytes recovered from medium-sized follicles showed evidence of germinal vesicle breakdown. In follicles containing high concentrations of progesterone, the incidence of atresia was high (38-48%) and most oocytes had resumed meiosis (> 97%).