title: Effects of oral contraceptives on body fluid regulation.
abstract: To test the hypothesis that estrogen reduces the operating point for osmoregulation of arginine vasopressin (AVP), thirst, and body water balance, we studied nine women (25 +/- 1 yr) during 150 min of dehydrating exercise followed by 180 min of ad libitum rehydration. Subjects were tested six different times, during the early-follicular (twice) and midluteal (twice) menstrual phases and after 4 wk of combined [estradiol-norethindrone (progestin), OC E + P] and 4 wk of norethindrone (progestin only, OC P) oral contraceptive administration, in a randomized crossover design. Basal plasma osmolality (P(osm)) was lower in the luteal phase (281 +/- 1 mosmol/kgH(2)O, combined means, P < 0.05), OC E + P (281 +/- 1 mosmol/kgH(2)O, P < 0.05), and OC P (282 +/- 1 mosmol/kgH(2)O, P < 0. 05) than in the follicular phase (286 +/- 1 mosmol/kgH(2)O, combined means). High plasma estradiol concentration lowered the P(osm) threshold for AVP release during the luteal phase and during OC E + P [x-intercepts, 282 +/- 2, 278 +/- 2, 276 +/- 2, and 280 +/- 2 mosmol/kgH(2)O, for follicular, luteal (combined means), OC E + P, and OC P, respectively; P < 0.05, luteal phase and OC E + P vs. follicular phase] during exercise dehydration, and 17beta-estradiol administration lowered the P(osm) threshold for thirst stimulation [x-intercepts, 280 +/- 2, 279 +/- 2, 276 +/- 2, and 280 +/- 2 mosmol/kgH(2)O for follicular, luteal, OC E + P, and OC P, respectively; P < 0.05, OC E + P vs. follicular phase], without affecting body fluid balance. When plasma 17beta-estradiol concentration was high, P(osm) was low throughout rest, exercise, and rehydration, but plasma arginine vasopressin concentration, thirst, and body fluid retention were unchanged, indicating a lowering of the osmotic operating point for body fluid regulation.
authors.affiliation: The John B. Pierce Laboratory, Department of Epidemiology and Public Health, and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06519, USA. nstach@jbpierce.org
authors.forename: N S
authors.initials: NS
authors.lastname: Stachenfeld
authors.forename: C
authors.initials: C
authors.lastname: Silva
authors.forename: D L
authors.initials: DL
authors.lastname: Keefe
authors.forename: C A
authors.initials: CA
authors.lastname: Kokoszka
authors.forename: E R
authors.initials: ER
authors.lastname: Nadel
mesh_terms: D000328:Adult; D000465:Algorithms; D001127:Arginine Vasopressin / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D001826:Body Fluids / Q000187:drug effects*; D003278:Contraceptives, Oral, Hormonal / Q000494:pharmacology*; D003681:Dehydration / Q000378:metabolism; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008598:Menstruation / Q000502:physiology; D010953:Plasma Volume / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D013894:Thirst / Q000502:physiology
chemical_list: D003278:Contraceptives, Oral, Hormonal; D001127:Arginine Vasopressin; D012964:Sodium