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Gender differences in endocrine responses to posture and 7 days of -6 degrees head-down bed restEndocrine regulation of fluids and electrolytes during 7 days of -6 degrees head-down bed rest (HDBR) was compared in male (n = 8) and, for the first time, female (n = 8) volunteers. The subjects' responses to quiet standing for 2 h before and after HDBR were also tested. In both sexes, diuresis and natriuresis were evident during the first 2-3 days of HDBR, resulting in a marked increase in the urinary Na(+)-to-K+ ratio and significant Na+ retention on re-ambulation. After the 1st day of HDBR, plasma renin activity (PRA) was increased relative to aldosterone (Aldo), plasma volume was decreased, and the renal response to Aldo appeared to be appropriate. Circulating levels of arginine vasopressin, cortisol, and ACTH were unchanged during HDBR. Plasma testosterone decreased slightly on day 2 of HDBR in males. The ratio of early morning ACTH to cortisol was lower in females than in males because ACTH was lower in females. Urinary cortisol increased and remained elevated throughout the HDBR in males only. There were no gender differences in the responses to 7 days of HDBR, except those in the pituitary-adrenal system; those differences appeared unrelated to the postural change. The provocative cardiovascular test of quiet standing before and after HDBR revealed both sex differences and effects of HDBR. There were significant sex differences in cardiovascular responses to standing before and after HDBR. Females had greater PRA and Aldo responses to standing before HDBR and larger Aldo responses to standing after HDBR than males.(ABSTRACT TRUNCATED AT 250 WORDS).
Document ID
Document Type
Reprint (Version printed in journal)
Vernikos, J. (NASA Ames Research Center Moffett Field, CA United States)
Dallman, M. F.
Keil, L. C.
O'Hara, D.
Convertino, V. A.
Date Acquired
August 22, 2013
Publication Date
July 1, 1993
Publication Information
Publication: The American journal of physiology
Volume: 265
Issue: 1 Pt 1
ISSN: 0002-9513
Subject Category
Aerospace Medicine
Distribution Limits
NASA Discipline Number 14-10
NASA Discipline Cardiopulmonary
NASA Discipline Regulatory Physiology
NASA Program Space Physiology and Countermeasures
NASA Discipline Number 18-10
Non-NASA Center