Prolactin as a factor in the uterine response to progesterone in rabbits

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Abstract
The direct effect of prolactin on uteroglobin production and on uterine endometrial estrogen and progesterone receptor concentrations was tested by using ovariectomized rabbit (at least 12 wk) treated with prolactin; prolactin + progesterone; prolactin + estradiol + progesterone; estradiol + progesterone; or progesterone alone. Prolactin treatment produced a significant (P < 0.05) increase in the concentration of cytosolic estrogen and progesterone receptors, restoring the concentrations to values found at estrus. The concentration of nuclear receptors remained low. In the remaining treatment categories there was no signifinct (P > 0.05) increase in the concentration of estrogen and progesterone receptors compared with those in ovariectomized controls. The sequential treatment of ovariectomized animals with prolactin + progesterone stimulated uteroglobin production to a concentration equal to that found in intact rabbits on the 5th day of pregnancy. This was not achieved by prolactin or progesterone alone or with estradiol. Prolactin may act as an essential factor in the rabbit uterine response to progesterone, perhaps by the modulation of progesterone receptor activity.