Relationship of Pituitary Prolactin and LH to Mammary and Uterine Growth of Pubertal Rats During the Estrous Cycle

Mammary and uterine development and their relationships to the pituitary content of prolactin and LH were studied during the five estrous cycles after vaginal opening in rats. Cumulative mammary and uterine growth was completed largely by the fourth estrous cycle after puberty. Although there was a lag of 1 day between peak mammary and uterine development, virtually all of this growth occurred during the estrogenic phase of the estrous cycle. Involutionary changes occurred in both organs during the progestational phase of the estrous cycle. Pituitary prolactin concentration was greater at proestrus (0.032 IU/mg) and metestrus (0.041 IU/mg) than at estrus (0.015 IU/mg) or diestrus (0.015 IU/mg). Pituitary LH concentration, which averaged 0.72, 0.31, 0.27, and 0.33 μ/mg at proestrus, estrus, metestrus, and diestrus, respectively, was correlated (r=0.58, p<.01) with changes in uterine RNA/DNA ratio.