Involvement of the adrenals in ovulation induced by unilateral ovariectomy in the rat

The aim of this study was to investigate the mechanisms of the stress-related ovulatory effects of unilateral ovariectomy (ULO) when performed on diestrus III at 10.00-11.00 hr in 5-day cyclic female rats. Ovulation evoked by ULO was suppressed in adrenalectomized rats. An increase in blood progesterone within 1 hour after ULO was observed in non adrenalectomized rats and suppressed in adrenalectomized rats. Pentobarbital (PB) treatment (30 mg/kg, ip) concomitant with ULO at 10.00-11.00 hr on diestrus III did not prevent progesterone to increase at 12.00-13.00 hr. A partial blockade of ovulation resulted from PB treatment from 13.00 hr to 18.00 hr on diestrus III. No blockade of ovulation occurred following PB injection at 23.00 hr. It was concluded that progesterone released from the adrenals following ULO constituted the trigger of ovulation during a critical period of diestrus III extending from 10.00 to 23.00 hr.