Lack of an Effect of the Pineal Gland, Olfactory Bulbectomy and Short Photoperiod on the Afternoon Prolactin Surge of the Ovariectomized, Estrogen Treated Rat1, 2

Abstract

The role of the pineal gland in the regulation of the daily afternoon surge of plasma prolactin in the ovariectomized, polyestradiol phosphate (PEP) treated rat was investigated. The effect of olfactory bulbectomy and/or short photoperiod (2L:22D), two procedures which may enhance pineal activity, was also examined. Control rats given PEP and maintained on 14L:10D cycles with the lights on from 0600-2000 h had afternoon surges of plasma prolactin with maximum levels between 1500-1900 h; the levels were similar whether the animals were sampled by decapitation or through catheters if the catheter extension was connected at 0700 h. However, if the catheter extension was connected at 1500 h, prolactin secretion at 1700 h was significantly inhibited. Pinealectomy or olfactory bulbectomy at the time of ovariectomy had no effect on the prolactin surges of ovariectomized, PEP treated rats whether they were maintained on 14L:10D or 2L:22D cycles. Control ovariectomized, PEP treated rats maintained on the 2L:22D photoperiod with the lights on from 1200-1400 h had prolactin surges similar to those in rats maintained on the standard 14L:10D photoperiod, but the maximum levels occurred between 1700-2100 h. It is concluded that the pineal gland and olfactory bulbs are not involved in the regulation of the afternoon prolactin surge of ovariectomized, estrogen treated rats. It is also concluded that short photoperiod has no effect on the magnitude of the surge.