High dietary cholecalciferol increases plasma 25-hydroxycholecalciferol concentration, but does not attenuate the hypertension of Dahl salt-sensitive rats fed a high salt diet

Abstract

The Dahl salt-sensitive rat, a model for salt-induced hypertension, develops hypovitaminosis D during high salt intake, which is caused by loss of protein-bound vitamin D metabolites into urine. We tested the hypothesis that high dietary cholecalciferol (5- and 10-fold standard) would increase plasma 25-hydroxycholecalciferol (25-OHD(3)) concentration (indicator of vitamin D status) of salt-sensitive rats during high salt intake. Salt-sensitive rats were fed 0.3% salt (low salt, LS), 3% salt (HS), 3% salt and 7.5 microg cholecalciferol/d (HS-D5), or 3% salt and 15 microg cholecalciferol/d (HS-D10) and sacrificed at week 4. Plasma 25-OHD(3) concentrations of the two groups of HS-D rats were similar to that of LS rats and more than twice that of HS rats. Urinary cholecalciferol metabolite content of HS-D rats was more than seven times that of HS rats. Systolic blood pressures of the hypertensive HS and HS-D rats did not significantly differ, whereas LS rats were not hypertensive. We conclude that high dietary cholecalciferol increases plasma 25-OHD(3) concentration, but does not attenuate the hypertension of salt-sensitive rats during high salt intake. Low salt intake may be necessary to both maintain optimal vitamin D status and prevent hypertension in salt-sensitive individuals.

Figure 1

High dietary cholecalciferol during high salt intake increases plasma 25- hydroxycholecalciferol (25-OHD₃) and urinary cholecalciferol metabolite content of Dahl salt-sensitive rats. Values are means ± SEM, n = 4 – 7 (plasma 25-OHD₃), n = 8 (urinary cholecalciferol metabolite content). Cholecalciferol: 7.5 μg (D5) or 15 μg (D10)/d. Overall effect of diet on plasma 25-OHD₃, P = 0.02, and urinary cholecalciferol metabolite content, P < 0.001. ^cLow salt vs. high salt-D, P < 0.05. ^bHigh salt vs. high salt-D5, P < 0.05. ^dHigh salt vs. high salt-D10, P < 0.05. Plasma 25-OHD₃ concentrations that were greater than twice the mean have been excluded from the plotted data (4 HS-D5, 1 HS-D10).

Figure 2

Plasma 1,25-dihydroxycholecalciferol and parathyroid hormone concentrations of Dahl salt-sensitive rats fed high dietary cholecalciferol during high salt intake. Values are means ± SEM, n = 6 – 8. Cholecalciferol: 7.5 μg (D5) or 15 μg (D10)/d.

Figure 3

High dietary cholecalciferol during high salt intake increases urinary calcium of Dahl salt-sensitive rats. Values are means ± SEM, n = 7 – 8. Cholecalciferol: 7.5 μg (D5) or 15 μg (D10)/d. Overall effect of diet, P < 0.001. Difference between any two diets, P < 0.001. ^bHigh salt vs. high salt-D5, P < 0.01. ^dHigh salt vs. high salt-D10, P < 0.001.