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Impaired Compensation for Salt-Induced Urinary Calcium Loss in a Space Flight ModelThe loss of urinary calcium (UCa) induced by high sodium (HiNa) diets is compensated for by an increase in net intestinal Ca absorption (abs.). To determine the capacity of the intestine to absorb Ca in a space flight model in which the formation of 1,25-dihydroxyvitamin D (1,25-D) is suppressed, we induced Ca loss with HiNa diets (8%) and restricted dietary Ca (0.2%). In 200 g rats with hind limbs unloaded by tail suspension (S), we examined intestinal Ca abs. by direct measurement in the duodenum (everted gut sac or S/M), vitamin D receptors (VDR) and Ca balance. We also measured serum ionized calcium (ICa), pH, parathyroid hormone (PTH) and 1,25D. PTH was related to ICa (r = -0.44, p is less than 0.02), pH (r = -0.47, p is less than 0.02) and %Ca abs. (r = -0.40, p is less than 0.05). 1,25-D was related to %Ca abs. (r = 0.60, p is less than 0.001) but not VDR or S/M. Effects of the model were lower serum 1,25-D (110 +/- 59 vs. 199 +/- 80 pg/ml, p is less than 0.005), %Ca abs. (83 +/- 6.9 vs. 93 +/- 3.2, p is less than 0.03) and Ca balance (27 +/- 0.2 vs. 30 +/- 0.3 mg/d, p is less than 0.001) in S than controls (C). The HiNa diet increased UCa excretion from 2 to 13% of dietary Ca. Responses to HiNa diets, compared to normal Na, revealed no differences in 1,25-D, Ca abs. or VDR. Ca balances were lower in HiNa (27 +/- 0.3 vs. 30 +/- 0.4 mg/d, p is less than 0.001) in spite of higher Ca intakes. The failure of S rats fed HiNa diets to increase Ca abs. in response to Na-induced Ca loss appears to be related to suppressed 1,25-D in the space flight model, the cause of which remains obscure.
Document ID
20010121574
Document Type
Conference Paper
Authors
Navidi, Meena
(NASA Ames Research Center Moffett Field, CA United States)
Harper, J. S.
(Houston Univ. TX United States)
Evans, J.
(Houston Univ. TX United States)
Fung, P.
(Houston Univ. TX United States)
Wolinsky, I.
(Houston Univ. TX United States)
Arnaud, S. B.
(NASA Ames Research Center Moffett Field, CA United States)
Wade, Charles E.
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Aerospace Medicine
Meeting Information
1994 Meeting of the American Sociaty of Bone and Mineral Research(Kansas City, MO)
Funding Number(s)
PROJECT: RTOP 199-26-12-02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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