![]() By selectively administering estradiol and/or progesterone while the subjects were suppressed, we isolated the effects of these hormones on the fluid and sodium regulatory systems during acute fluid or osmotic challenges. The suppression is followed by controlled administration of estradiol, progesterone, or combined estradiol-progesterone to physiological levels. These protocols, in effect, pharmacologically “oophorectomize” subjects for a short easily reversible period. 1) to suppress reproductive function (and thus estrogens, progesterone, and gonadotropins). A series of studies described in this article used a newer paradigm to control the levels of sex hormones through the use of either a gonadotropin-releasing hormone (GnRH) agonist or antagonist ( Fig. However, when examining the interaction of these hormones and body fluid regulation under these study paradigms, estradiol or progesterone were elevated or suppressed simultaneously, so we did not isolate their individual effects. In our early studies, we determined reproductive hormone effects on body water regulation system in young women by examining responses to fluid perturbations either during the different phases of the menstrual cycle or during administration of oral contraceptives. The study of reproductive hormone effects on physiological systems is complex in young women because of hormonal fluctuations over the course of the menstrual cycle ( Fig. Moreover, the impact of sex hormones on body fluid and sodium regulation has important implications for a number of syndromes for which women are at risk, including orthostatic hypotension, insulin resistance, polycystic ovary syndrome, and neurological consequences from postoperative ( 8) and exercise-associated hyponatremia ( 1). Receptors for estrogens and progesterone are found in nonreproductive tissue involved in fluid regulation, such as the hypothalamus ( 10, 21), the cardiovascular system ( 6, 19), and the kidney tubules ( 6). One mechanism by which estrogens or progesterone may impact physiological systems is through regulation of body fluids and sodium content. For example, premenopausal women have delayed and less severe manifestation of cardiovascular diseases than do men ( 13), and although there continues to be some controversy surrounding hormone replacement in postmenopausal women, hormone replacement therapy is usually associated with improved cardiovascular function in perimenopausal and postmenopausal women ( 6, 19). ![]() There are clear sex differences in risk factors for a number of syndromes and diseases in addition to sex differences in the function of many physiological systems.
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