AJP - Endocrinology and Metabolism, Vol 259, Issue 3 E319-E326, Copyright © 1990 by American Physiological Society
1,25(OH)2D response to combined zinc and phosphorus depletion in rats
P. L. Kimmel, D. W. Watkins, E. Slatopolsky and C. B. Langman
Rita Gusack Laboratory, Department of Medicine, George Washington University Medical Center, Washington, DC 20037.
To investigate the role of zinc depletion in the response of calcitriol to
a single provocative stimulus, we studied vitamin D metabolites,
parathyroid hormone (PTH), and mineral balance during phosphorus depletion
in animals with different zinc nutritional status. Male Lewis rats (66)
were pair fed normal phosphorus (NP), zinc-replete (+) or -deplete (-)
diets for 2 wk. Thereafter, one-half of each paired group underwent 1 wk of
phosphorus depletion (LP). Zinc-deplete animals had lower plasma zinc, and
phosphorus-deplete animals had lower plasma phosphorus concentrations than
respective nutritionally replete controls. Plasma calcium, PTH, and
25-hydroxycholecalciferol concentrations were similar in all four groups at
end of experiment. Mean plasma 1,25(OH)2D concentration increased 80% from
35 +/- 3 to 63 +/- 9 pg/ml (P less than 0.007) when values were compared
before and after phosphorus restriction in zinc-replete animals (LP +
group). The 7.9% increase from 35 +/- 4 to 38 +/- 4 pg/ml in 1,25(OH)2D
concentration in animals with combined zinc and phosphorus depletion (LP-)
was not significant. External calcium balance, however, was maintained in
the combined zinc and phosphorus-deplete group. We conclude that zinc
depletion limits the increase in plasma 1,25(OH)2D concentration associated
with phosphorus depletion. The mechanism is unknown but may involve an
effect of zinc on renal 25(OH)D 1-alpha-hydroxylase synthetic activity.
