ASGSB 2003 Annual Meeting Abstracts


URINARY 25-HYDROXYVITAMIN D BINDING ACTIVITY IS DIRECTLY CORRELATED WITH URINARY SODIUM OF AFRICAN-AMERICAN MEN DURING HEAD-DOWN TILT BED REST.  S. Cephas1, H.R. Scott1, P.  Sayavongsa1, M. Pasquali3, E. Schwartz3, R. Lapu-Bula2, E. Ofili2, and M. Thierry-Palmer1.  Dept of  1Biochemistry and 2Medicine,  Morehouse  School of Medicine, Atlanta and 3Dept of Pathology,  Univ of Utah,  Salt Lake City.  

   The Dahl salt-sensitive rat, a model for salt-induced hypertension, excretes protein-bound 25-hydroxyvitamin D (25-OHD) into urine during low salt intake and excretion is markedly increased during high salt intake.  Since the prevalence of salt sensitivity in the African-American population is greater than that in the Caucasian-American population, we determined whether African-American men  (29  + 2 years old, 122  + 3 mm Hg, n = 19) involved in a head-down tilt bed rest study excreted 25-OHD binding protein(s) into urine. The subjects were fed a low salt  (50 mmol/day, 7 subjects) or high salt (200 mmol/day, 12 subjects) diet during seven days of head-down tilt bed rest.    Plasma was collected at day 0 and day 7 and 24 h urine was collected at day 1 and day 7.   Urinary 25-OHD binding activity varied directly with urinary sodium (r = 0.70, P = 0.001), as did urinary protein  (r = 0.56, P = 0.0004).  Baseline values for plasma 25-OHD (26 + 4 nmol/L), 24,25-dihydroxyvitamin D (2.4 + 0.4 nmol/L), and parathyroid hormone  (30  + 3 pg/mL) were not significantly affected by seven days head-down tilt bed rest or by high salt intake.  Plasma 1,25-dihydroxyvitamin D concentration of subjects fed the low salt diet was significantly lower at day 7 than at baseline  (55 + 17 vs. 120  + 10 pmol/L, P = 0.001).  Urinary deoxypyridinoline, a marker of bone resorption, was significantly increased from day 1 to day 7 of head-down tilt bed rest (P = 0.01).    In summary, increased pyridinium cross-links excretion was the major change related to bed rest.  Further studies are necessary to determine whether there is a contribution of bed rest, as well as salt, to the urinary excretion of 25-OHD binding protein(s). 

(Supported by NASA NCC9-112)


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