General Physiological Activities of Estrogen

Abstract

Estrogen has multiple physiological functions and is a central modulator at the molecular, cellular, and behavioral level. Of great importance is estrogen’s responsibility for sexual differentiation and maturation as well as for the growth of female secondary sexual organs. Estrogen has a variety of effects on the metabolism of macromolecules in both the vagina and the uterus. Among other activities in the mammary gland, estrogens together with progesterone regulate the lactogenesis of the gland. But doubtless, the female sex hormone has multiple functions all over the body due to the fact that ERs are expressed in a variety of tissues. Undisputed is the role of estrogen during sexual differentiation and maturation. There is a great body of literature on the function of estrogen in human sex organs such as in the ovaries and in reproduction as well as on the basic findings of the interac­tion of estrogens with brain function. Therefore this discussion will end here by giving reference to the literature (for review: James et al., 1976; McEwen et al., 1987; Genazzani et al., 1992; Priest and Pfaff, 1995; Pfaff, 1997; Redmond, 1999). Based on the research of the last two decades, estrogen is also active in the CNS and modifies various neurophysiological processes. Estrogen’s main target tissue in the brain with respect to sex-related processes is the hypothalamus. The hypothalmus is an endocrine gland and secretes signal molecules which act on pituitary action (see page 17). It takes a central part in the regulation of other glands including the ovaries and thyroids. Consequently, hypothalamic functions control body temperature, blood sugar, fat metabolism and other central conditions. Estrogen is an important regulator of the hypothalamic-hypophyseal-system and modulates the secretion of luteinizing hormone (LH) and of follicle stimulating hormone (FSH). Of course, estrogen is part of various feedback mechanisms in the hypothalamus and has various activities (for review: Blaustein and Olster, 1989; Baulieu and Kelly, 1990; McCarthy and Pfaus, 1996; Horvath et al., 1997; Herbison, 1998; Frohlich et al., 1999; Etgen et al., 1999). During the development of the mammalian nervous system estrogen affects various processes at different levels (for review: Beyer, 1999).