Exogenous 25-hydroxycholecalciferol does not attenuate salt-induced hypertension

We have reported that an inverse relationship exists between blood pressure and plasma concentration of 25-hydroxyvitamin D, the precursor of the horm onal form of vitamin D, for Dahl salt-sensitive rats fed a high salt diet. Plasma 25-hydroxyvitamin D concentrations decreased with time on the diet, as blood pressure increased. Experiments were conducted to determine whethe r the blood pressure increase of salt-sensitive rats fed a high salt diet c ould be attenuated by exogenous 25-hydroxycholecalciferol. Dahl salt-sensit ive rats were fed a high salt diet and administered exogenous 25-hydroxycho lecalciferol via subcutaneously implanted Alzet pumps. Exogenous 25-hydroxy cholecalciferol (various doses from 28 to 80 mu g/kg body weight-day) had n o significant effect on the blood pressure of vitamin D-replete rats fed a high salt diet for 15 days. When exogenous 25-hydroxycholecalciferol (28 an d 60 mu g/day-kg body weight) was administered to vitamin D-depleted salt-s ensitive rats, plasma 25-hydroxyvitamin D concentrations of the rats fed a low salt diet (26 +/- 2 and 59 +/- 6 nM) were proportional to the 25-hydrox ycholecalciferol concentration in the pumps. Plasma 25-hydroxyvitamin D con centrations of the rats fed a high salt diet (18 +/- 1 and 23 +/- 3 nM) wer e not proportional to the 25-hydroxycholecalciferol concentration in the pu mps, but were inversely proportional to the blood pressure of the rats. The se data indicate no ameliorating effect of exogenous 25-hydroxycholecalcife rol on salt-induced hypertension, but accelerated metabolism and/or clearan ce of 25-hydroxycholecalciferol in salt-induced hypertension. (C) 1998 Else vier Science Ltd. All rights reserved.