PLASMA 25-HYDROXYVITAMIN-D CONCENTRATIONS ARE INVERSELY ASSOCIATED WITH BLOOD-PRESSURE OF DAHL SALT-SENSITIVE RATS

Dietary salt is a contributing factor to the development of hypertensi on in individuals who are salt-sensitive. The vitamin D endocrine syst em has been reported to modulate vascular structure and function. Sinc e elderly hypertensive females with low plasma renin activity, typical of salt-sensitivity, had significantly lower 25-hydroxyvitamin D conc entrations compared with normotensive elderly and young females, we ha ve used Dahl salt-sensitive and salt-resistant rats fed high (80 g/kg diet) and low (3 g/kg diet) salt diets as models to examine the relati onship between salt-sensitivity and 25-hydroxyvitamin D, the precursor of the hormonal form of vitamin D, 1,25-dihydroxyvitamin D. Plasma 25 -hydroxyvitamin D concentrations of salt-resistant rats were unaffecte d by a high salt diet, but plasma 25-hydroxyvitamin D concentrations o f salt-sensitive rats were significantly reduced within three weeks to lower than 25%. There was a negative association between plasma 25-hy droxyvitamin D concentrations of salt-sensitive rats and the number of days that the rats were fed a high salt diet (r = - 0.98, P < 0.02) a nd a positive association between blood pressure and the number of day s that the rats were fed a high salt diet (r = 0.97, P< 0.05). An inve rse relationship was found between plasma 25-hydroxyvitamin D concentr ations and blood pressure (r = - 0.99, P< 0.01). Spontaneously hyperte nsive rats did not have low plasma 25-hydroxyvitamin D concentrations, suggesting that reduction of plasma 25-hydroxyvitamin D concentration might be specific to salt-induced hypertension. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.