New insights into the normal menstrual cycle-regulatory molecules

Abstract

Although the growth and regression of the endometrium is primarily a function of the ovarian hormones, recent studies indicate a potential autocrine/paracrine role for regulatory molecules. Thus, growth factors, angiogenesis stimulating factors and proliferating cell markers are high in the proliferative phase endometrium contributing to its regeneration. At the same time, other proteins promote endometrial cell survival by preventing extracellular matrix degradation and apoptosis. As glandular proliferation persists in the early secretory phase of the menstrual cycle, the activity of some proteins stimulating growth remains unchanged, but declines significantly thereafter, shifting the balance between proliferation and apoptosis in favour of apoptosis. During this period, several other regulatory substances are expressed at high levels, suggesting a role in endometrial maturation. If, however, implantation of a fertilized ovum fails to take place, menstruation occurs probably as the result of matrix metalloprotinases which antagononizes the anti-degradation factors (inhibitors of metalloproteinases). This review examines the changing endometrial patterns of a normal menstrual cycle in relation to these regulatory molecules.