Cell Renewal in Hormone-responsive Tissues Turing the Estrous Cycle

Abstract

In females, specific patterns of hormone secretion characterize the different phases of the sexual cycle and consequently, specific endocrine context influences the function of every hormone-responsive organ at each phase of the cycle. In rodents, estradiol plasma levels begin to rise during diestrus to induce a peak of FSH, LH and prolactin secretion in the afternoon of proestrus. At this time, the ovary switches to progesterone secretion whereas anterior pituitary hormone secretion remains basal during the following estrus and diestrus stages. This hormone profile determines cell life and death in different tissues in order to maintain their functions and homeostasis. Among the hormones that fluctuate during the estrous cycle, estrogens, progesterone, gonadotropins and prolactin have been implicated in the regulation of proliferation and apoptosis in organs related to reproductive functions such as the anterior pituitary gland, ovary, uterus, oviduct and mammary gland. For example, estradiol and prolactin induce apoptosis of anterior pituitary cells at proestrus, preserving the number of cells that proliferated in the gland during the previous estrus stage. However, estrogens and prolactin stimulate proliferation of endometrial and mammary gland epithelia, preparing these tissues for implantation or lactation, respectively. Each tissue responds differentially to hormone variations along the estrous cycle. The aim of this review is to summarize the specific regulation of cell renewal in these hormone-responsive tissues occurring during the estrous cycle.