Dahl salt-sensitive rats develop hypovitaminosis D and hyperparathyroidism when fed a standard diet.
The Dahl salt-sensitive rat (S), a model for salt-sensitive hypertension, excretes protein-bound 25-hydroxyvitamin D (25-OHD) into urine when fed a low salt diet. Urinary 25-OHD increases during high salt intake. We tested the hypothesis that continuous loss of 25-OHD into urine would result in low plasma 25-OHD concentration in mature S rats raised on a standard diet. Dahl S and salt-resistant (R) male rats were raised to maturity (12-month-old) on a commercial rat diet (1% salt) and switched to 0.3% (low) or 2% (high) salt diets 3 weeks before euthanasia. Urine (24 h) was collected at the end of the dietary treatments. Urinary 25-OHD and urinary 25-OHD binding activity of S rats were three times that of R rats, resulting in lower plasma 25-OHD and 24,25-dihydroxyvitamin D concentrations in S rats than in R rats (P < 0.001). Plasma parathyroid hormone concentrations of S rats were twice that of R rats. S rats fed 2% salt had higher plasma 1,25-dihydroxyvitamin D concentrations than those fed 0.3% salt (P = 0.002). S rats excreted more calcium into urine than R rats (P < 0.001) and did not exhibit the expected calciuric response to salt. Proteinuria of the S rats was three times that of the R rats, suggesting kidney damage in the S rats. Low plasma 25-OHD and 24,25-dihydroxyvitamin D and high plasma 1,25-dihydroxyvitamin D and PTH concentrations seen in the mature S rats have also been reported for elderly patients with low-renin (salt-induced) hypertension. An implication of this study is that low vitamin D status may occur with age in salt-sensitive individuals, even when salt intake is normal.
Thierry-Palmer
Myrtle
M
Department of Biochemistry, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA. mthierry-palmer@msm.edu
Cephas
Stacy
S
Sayavongsa
Phouyong
P
Doherty
Akins
A
Arnaud
Sara B
SB
D000818:Animals; D004032:Diet; D004591:Electrophoresis, Polyacrylamide Gel; D006961:Hyperparathyroidism / Q000209:etiology*; D008297:Male; D051381:Rats; D020303:Rats, Inbred Dahl; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood / Q000652:urine; D014808:Vitamin D Deficiency / Q000209:etiology*
D014807:Vitamin D; C104450:25-hydroxyvitamin D