EFFECTS OF SODIUM DEPLETION ON TISSUE CONCENTRATIONS OF THE NATRIURETIC HORMONE VASOACTIVE-INTESTINAL-PEPTIDE

1. Variations in dietary sodium intake have been shown to affect the p lasma concentration, the metabolic clearance rate and secretion rate o f vasoactive intestinal peptide (VIP). In this study we sought to dete rmine the effect of sodium depletion on the concentration of VIP in pl asma and in three tissues, namely heart, lung and kidney. 2. Male Spra gue-Dawley rats were placed on low or normal sodium diets and drinking water adlibitum. A third group was placed on a low salt diet and in a ddition were given frusemide, 1 mg/kg per day in the drinking water. A fter 7 days the rats were killed, a blood sample collected and tissues harvested, VIP concentrations were determined by radioimmunoassay on unextracted plasma and in tissue after extraction. 3. There were signi ficant differences between the three groups in the concentration of VI P in the lung (P<0.0005), kidney (P<0.005) and plasma (P<0.025) but no t the heart. In the group that received frusemide and the low sodium d iet, VIP in the lung was significantly lower than the low sodium (P<0. 005) and normal sodium (P<0.0001) groups, Similar differences were not ed in the kidney (frusemide vs low sodium, P<0.001; frusemide vs norma l, P<0,01) and plasma (frusemide vs low sodium P<0.001, frusemide vs n ormal P<0.05). 4. We conclude that sodium depletion decreases the conc entration of VIP in plasma and in its metabolizing tissues.