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 plasma concentration, the metabolic clearance rate and secretion rate of vasoactive intestinal peptide (VIP). In this study we sought to determine the effect of sodium depletion on the concentration of VIP in plasma and in three tissues, namely heart, lung and kidney. 2. Male Sprague-Dawley rats were placed on low or normal sodium diets and drinking water ad libitum. A third group was placed on a low salt diet and in addition were given frusemide, 1mg/kg per day in the drinking water. After 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 significant differences between the three groups in the concentration of VIP in the lung (P < 0.0005), kidney (P < 0.005) and plasma (P < 0.025) but not the heart. In the group that received frusemide and the low sodium diet, VIP in the lung was significantly lower than the low sodium (P < 0.005) and normal sodium (P < 0.0001) groups. Similar differences were noted in the kidney (frusemide vs low sodium, P < 0.001; frusemide vs normal, P < 0.01) and plasma (frusemide vs low sodium P < 0.001, frusemide vs normal P < 0.05). 4. We conclude that sodium depletion decreases the concentration of VIP in plasma and in its metabolizing tissues.