HYPERTENSION DEVELOPMENT IN DAHL-S AND DAHL-R RATS ON HIGH-SALT LOW POTASSIUM DIET - CALCIUM, MAGNESIUM AND SYMPATHETIC NERVOUS-SYSTEM

Dietary combination of high salt with low potassium (HSLK) exacerbates hypertension development in Dahl salt-sensitive (S) rats, and produce s a mild degree of hypertension in otherwise salt-resistant (R) rats. Increased blood pressure in both strains is associated with increased urinary excretion of calcium and magnesium. The objective of this stud y was to determine the effect of blood pressure on body balance of the se ions in Dahl rats on HSLK diet. Two groups of S and two groups of R weanlings were all placed on HSLK diet (NaCl=8%, K=0.2%) for eight we eks. One group of each strain was subjected to chemical sympathectomy with 6-hydroxydopamine (6-OHDA) to counteract hypertension development . Urinary norepinephrine was used to determine efficacy of 6-OHDA trea tment. Systolic blood pressures of conscious animals were measured dai ly throughout the study. The last three days on the diet were used to determine total dietary intake and urinary as well as fecal excretion of sodium, calcium and magnesium. At the end of the study, extracellul ar fluid volume, serum aldosterone and parathyroid hormone were analyz ed. Final systolic blood pressures in the 4 groups were as follows: S = 235+/-9 mmHg (n=9); R = 155+/-3 mmHg (n=8); 6-OHDA S = 151+/-6 mm Hg (n=8); 6-OHDA R = 117+/-6 mm Hg. Chemical sympathectomy decreased blo od pressure in both S and R rats. There was no indication of sodium ac cumulation in S rats. Associated with reduced parathyroid hormone leve ls the S strain had significantly less positive balance for calcium th an the R strain, primarily due to increased urinary excretion. A less positive balance for magnesium was also observed, due mainly to relati vely reduced intestinal absorption of the ion. We conclude that the HS LK diet is associated with inappropriate activation of the sympathetic nervous system and increased arterial pressure in both strains. In ad dition, since divalent cations may influence blood pressure, we sugges t that the observed abnormalities in calcium and magnesium metabolism might independently promote hypertension development in the S strain.