Renal excretory function, atrial natriuretic peptide (ANP) and plasma renin activity (PRA) during long-term sodium loading in rats.

The effect of chronic sodium loading on the level of plasma atrial natriuretic peptide (ANP) and on plasma renin activity (PRA), as well as on the renal excretory function was studied. Fifty-six standardly bred Long Evans rats were divided into three experimental groups: controls, rats drinking 170 mmol NaCl/l solution instead of water, and rats consuming food with high sodium content (850 mmol NaCl/kg) for 21 days. During the study, we measured the amount of fluid intake, the parameters of the renal function: diuresis (VU); sodium, potassium and cloride excretion (UNa V, UKV and UClV), and the dynamics of body mass. On the 21st day the animals were sacrificed by decapitation. Plasma ANP and PRA were determined radioimmunologically. Packed cells volume and plasma Na and Cl concentrations were measured. The data showed a full compensation in sodium balance: the body mass dynamics in the three groups was similar; no changes in packed cells volume and plasma electrolytes were seen; UNaV and UClV were significantly increased in the groups with high sodium intake. PRA was significantly depressed in the two groups while ANP did not show any real changes. We concluded that it is PRA and not ANP that might participate in the regulation of chronic sodium balance.