Calcium and calcium regulating hormones in the "prehypertensive" Dahl salt sensitive rat (calcium and salt sensitive hypertension)

The purpose of this study was to determine if alterations of calcium and calcium regulating hormones precede the onset of NaCl induced hypertension in the Dahl salt sensitive (S) rat. After a 5 day balance study, serum ionized calcium, PTH, and 1,25 dihydroxy vitamin D concentrations were measured in Dahl-S and salt resistant (R) rats that had been maintained on a "normal" (1%) or high (7%) NaCl intake. Blood pressure was higher in Dahl-S than R (P less than .01), but was not affected by 5 days of high NaCl. On both NaCl intakes, urine calcium excretion was increased, serum calcium was decreased, and serum PTH and 1,25 dihydroxy vitamin D were increased in Dahl-S compared to Dahl-R (P less than .01). On the high NaCl intake, fecal calcium was greater in Dahl-S than in Dahl-R, and net 5 day calcium balance was less positive in Dahl-S (P less than .05). In contrast to NaCl, a high dietary intake of sodium with anions other than chloride (NaAA) fails to produce hypertension in the Dahl-S rat. NaAA loading resulted in decreased urine calcium excretion (P less than .01), and after 5 days of the high NaAA diet, serum calcium and PTH did not differ in Dahl-S and Dahl-R. Thus, alterations of calcium, PTH, and vitamin D precede NaCl-induced hypertension in Dahl-S. These alterations may contribute to the development of hypertension in this animal model.