Background: Dopamine D(2) receptors (D(2)Rs) are expressed in the kidney. It has not been determined whether D(2)Rs are involved in the mechanism of sodium handling and blood pressure (BP) control.
Methods: The function of D(2)Rs was investigated in mice disrupted with D(2)R gene (D(2)KO mice). Six-week-old male D(2)KO mice and wild-type (WT) mice were fed high-salt (4% NaCl) or low-salt (0.01% NaCl) diets for 8 weeks.
Results: Before starting the metabolic diet, there were no significant differences in body weight, food consumption, and 24-h urine excretions of creatinine, sodium and potassium. The high-salt diet caused a significant elevation in systolic BP in D(2)KO mice but not in WT mice. Calculation of sodium and potassium balances revealed a significantly high level of sodium retention in D(2)KO mice placed on the high-salt diet. Twenty-four-hour urine norepinephrine excretions and heart rates, indicators of sympathetic activity, were not different in D(2)KO and WT mice on the high-salt diet. Administration of nemonapride, a specific D(2)-like receptor antagonist, to WT mice given 0.9% NaCl in drinking water caused suppression of urinary sodium excretion but had no effect in mice without salt loading.
Conclusions: These results suggest that D(2) receptors promote sodium excretion during a period of high salt intake. A defect in this mechanism may result in sodium-dependent BP elevation.