Abstract
Two daily surges of prolactin were found in the rat during pseudopregnancy induced by sterile copulation or cervical stimulation. Both surges disappeared after day 11 of pseudopregnancy. However, when high progesterone levels (70-90 ng/ml) were maintained with silastic implants filled with progesterone after day 8 of pseudopregnancy, both prolactin surges continued to occur until removal of the implants on days 13 or 15. During pseudopregnancy induced by a pituitary isograft, serum prolactin concentrations were elevated at all times when measured during the day, and the typical prolactin surges of normal pseudopregnancy were not found. The percentage of animals which remained pseudopregnant increased when extirpation of the kidney with the pituitary isograft occurred on day 4 instead of day 2 of pseudopregnancy. After the removal of the pituitary isograft on day 5, a decrease in basal prolactin concentrations was observed. However, in 94% of these animals pseudopregnancy continued, and both daily prolactin surges were measured after this operation in the rats remaining pseudopregnant. In animals bearing fetuses in one uterine horn and a deciduoma in the other, diurnal prolactin surges were observed only until day 8 of pregnancy. However, elevated concentrations of prolactin were found at 1800 h until at least day 15 in pseudopregnant rats bearing unilateral deciduomata. It is concluded that 1) the disappearance of the prolactin surges at the end of pseudopregnancy probably is caused by the decline in luteal activity, 2) elevated levels of prolactin secreted by a pituitary isograft or the presence of uterine conceptuses have a negative influence on the twice daily release of prolactin by the in situ pituitary gland, and 3) copulation or cervical stimulation during the period of estrus is not a prerequisite for the occurrence of the daily surges of prolactin during the luteal phase once luteal function has become apparent. (Endocrinology102: 1190, 1978).
Published Version
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