Interrelation between the renal sympathetic nerve and atrial natriuretic peptide in conscious long Evans rats subjected to sodium restriction.

The renal excretory function and plasma renin activity (PRA) were studied in conscious rats on a low sodium diet (25 mmol/kg) after atrial natriuretic peptide (ANP) infusion (100 ng/kg b.w./min) for 80 min through a catheter implanted in the right atrium. The half of the animals were with bilateral kidney denervation. The rats were housed every day from 8 a.m. to 2 p.m. in individual metabolic cages for urine collection and Na, Cl, osmolality and endogenous creatinine determination. At the last day of the experiments after the ANP infusion, blood was taken from the heart for electrolytes, endogenous creatinine and PRA. The effect of denervation was monitored by measuring of noradrenaline in kidney homogenate. The data indicated that even at low sodium diet ANP stimulates the diuresis and sodium excretion without changing the glomerular filtration rate (GFR). The kidney denervation combined with ANP infusion increased twice the diuresis and four times sodium excretion vs. the control animals. In the same time PRA was decreased by about 70%. We assume that the low sodium diet attenuates the effect of ANP in respect to the excretory function. This inhibitory effect is amplified by the renal sympathetic nerves. The decrease of PRA and possibly the increased activity of renal receptors after the denervation could explain the data obtained.