Altered calcium homeostasis in Dahl hypertensive rats: physiological and biochemical studies

Abnormal calcium (Ca) homeostasis has been reported in essential hypertension and in the Okamoto-Aoki strain of spontaneously hypertensive rats. These abnormalities include increased urinary excretion of calcium and decreased ionized serum calcium (Ca2+). To pursue these abnormalities we studied the chronology of urinary excretion of electrolytes in a genetically homogeneous strain of hypertensive rat, the Dahl/Rapp salt sensitive (S) and resistant (R) rat (at ages 3, 5, 7, 9, 12, 20 and 32 weeks). We also characterized the renal adenylate cyclase-cAMP system by measuring urinary cAMP excretion and adenylate cyclase response to membrane receptor agonists in renal membranes from S and R rats at day 2 and at 6 and 28 weeks of age. Urinary calcium excretion was higher in S than in R at 3, 5 and 7 weeks (0.48 +/- 0.04 versus 0.24 +/- 0.01 mg/mg creatinine at 7 weeks, P less than 0.01). Sodium and phosphorous excretion were lower in S than in R rats at 5, 7, 9, and 12 weeks, and at 5, 7, 9, 12, 20 and 32 weeks, respectively. Potassium excretion was similar in the two groups. Plasma ionized calcium was lower in S than in R rats (3.9 +/- 0.1 versus 4.5 +/- 0.1 mg/dl, P less than 0.01) only at 7 weeks of age. Plasma parathyroid hormone (PTH) was not different between S and R rats. Cyclic AMP excretion and the renal adenylate cyclase response to PTH when referenced to basal activity was lower in S than in R rats at all ages.(ABSTRACT TRUNCATED AT 250 WORDS)