Abstract
Experiments were conducted to investigate the mechanism whereby intrapituitary implantation of crystalline estradiol benzoate (EB) on diestrus-2 advances ovulation by 1 day in rats showing 5-day estrous cycles; or 4- day rats converted to a 5-day cycle by progesterone on metestrus (diestrus-1). Sodium pentobarbital early in the afternoon of the day following implantation prevented advancement of ovulation. It was restored in 50% of animals after administration of a submaximal dose of an ovine gonadotropin releasing factor preparation. To determine the required period of action of estrogen on the pituitary, implants were allowed to remain in situ for different periods of time at different stages of the cycle. Twenty-four hr implantation from the morning of diestrus-2 was effective, in contrast to similar implantation 1 day later. When implants were placed for shorter periods of time on diestrus-2, it was found that implantation from 1 to 5 PM advanced ovulation in all of 9 rats tested. This period of expos...
Published Version
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