Hormonal Changes

Menstrual cycle hormonal changes can also influence drug absorption, distribution, metabolism, and elimination, and oral contraceptive use can interfere with the metabolism of many drugs. Due to the absolute preclusion of pregnancy in space, many female astronauts choose oral contraceptives during the training period, and most continue to use them while on orbit. Changes in the renal, cardiovascular, hematological, and immune systems during menstruation are well known, and these physiological changes could influence the pharmacokinetics and pharmacodynamics of drugs by altering such variables as protein binding and volume of distribution of drugs, which could significantly worsen disease severity.

REPRODUCTION

Normal Menstrual Function
Because space shuttle flights are considerably shorter than the average menstrual cycle length, no on-orbit studies have been done to determine the impact of microgravity on normal hypothalamic/pituitary/ovarian axis function. The primary concern is that anovulation might occur, resulting in continuous estrogen exposure, endometrial hyperplasia, and possibly menorrhagia. Second, there is some concern that hypothalamic amenorrhea and reduced estrogen levels could occur. The reason for concern is that the exercise necessary for long-term cardiovascular and musculoskeletal fitness may be strenuous enough to cause hypothalamic-induced hypogonadism with reduced serum estrogen levels. The combined effect of hypoestrogenemia and spaceflight-related calcium loss could lead to increased osteoporosis risk.

Menstrual Efflux and Retrograde Menstruation Many women normally experience some retrograde intra-abdominal bleeding during menses. Because of the effects of gravity, the blood products and cellular debris usually stay confined to the pelvis. The development of endometriosis is multiface
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Contact: Donna Krupa
djkrupa1@aol.com
703-527-7357
American Physiological Society
30-Nov-2001