Testosterone-induced oestrous cycle blockade in the rat: no evidence for prolactin involvement

The relation between testosterone-induced oestrous cycle disruption and prolactin (Prl) secretion was studied in the female rat. Testosterone propionate (TP) injection on dioestrus 2 (day 0) of 4-day cycles induced cycle interruption for 12 days. A diurnal pattern of Prl secretion was observed from day 1 to day 6 with high levels in the afternoon and low levels in the morning. Cycle interruption also occurred in TP treated females given a dose of bromocriptine (BRC) known to completely block Prl secretion. Impairment of follicular growth resulted from TP treatment and from TP and BRC treatment as well. Until resumption of prooestrous, the follicular size did not exceed that noted during the dioestrous period of the cycle. Despite resumption of follicular growth from day 9 until day 14, ovulation only took place in a small number of animals. These results indicate that the antigonadotropic effects of Prl were not responsible for cycle disruption in our experimental model and that other mechanisms were in itself sufficient for the disruption. This was discussed in the light of previous findings in our laboratory.