AJP - Endocrinology and Metabolism, Vol 253, Issue 6 E675-E683, Copyright © 1987 by American Physiological Society
Involvement of vitamin D3 with cardiovascular function. II. Direct and indirect effects
R. E. Weishaar and R. U. Simpson
Department of Pharmacology, University of Michigan, Ann Arbor 48109.
To determine whether the changes in cardiovascular function that accompany
vitamin D3 deficiency are the direct result of hypovitaminosis D3 or a
response to the hypocalcemia that accompanies vitamin D3 deficiency, rats
were maintained for 9 wk on a vitamin D3-deficient diet containing either
low (0.4%) calcium or high (2.5%) calcium to prevent hypocalcemia. Rats
were also maintained on the low-calcium, vitamin D3-deficient diet for 9 wk
and then transferred to diets designed to reverse hypocalcemia or vitamin
D3 deficiency. The results demonstrate that the changes in in vitro cardiac
contractile function that accompany vitamin D3 deficiency 1) could not be
prevented by preventing the hypocalcemia that normally accompanies vitamin
D3 depletion or 2) could not be reversed by restoration of serum calcium to
normal levels after the initial period of vitamin D3 depletion. In
contrast, the change in in vitro vascular muscle contractile function
observed in vitamin D3-deficient, hypocalcemic rats could be prevented by
maintaining serum calcium at normal levels and also reversed by restoration
of serum calcium to normal after an initial period of vitamin D3
deficiency. These observations indicate that hypocalcemia does not account
for the changes in cardiac contractile function that result from vitamin D3
depletion and suggest a direct role for vitamin D3 or its metabolite
1,25-dihydroxyvitamin D3 in regulating cardiac contractility. Possible
mechanisms underlying this direct effect were also explored.
