The effect of dietary sodium on the concentrations of vasoactive intestinal peptide in plasma and lung.

Abstract

STUDY OBJECTIVES: In this study, we sought to determine whether changes in the concentration of vasoactive intestinal peptide (VIP) in the lung might explain the increase in bronchial reactivity associated with high sodium diets. DESIGN: Male Sprague-Dawley rats, eight in each group, were placed on low-sodium, normal-sodium, or high-sodium diets and distilled drinking water ad libitum for 7 days. On the day of study, blood was sampled to determine plasma VIP concentration and the lungs were harvested and snap frozen in liquid nitrogen. VIP was measured in plasma and tissue extracts by radioimmunoassay. RESULTS: The VIP concentrations in both lung and plasma varied with dietary sodium. Plasma VIP level was significantly higher in the rats that had received the low-sodium diet (51.45 +/- 7.35 pmol L-1) than in the rats that had received the high-sodium diet (29.84 +/- 6.83; p < 0.05). In the lung, VIP level was greater in the rats that had received the normal-sodium diet (378.13 +/- 41.68 fmol/g) than in rats that had received either the low-sodium diet (137.30 +/- 26.11 fmol/g; p < 0.0005) or the high-sodium diet (182.64 +/- 28.63 fmol/g; p < 0.005). CONCLUSIONS: The lower plasma and pulmonary concentrations of VIP observed in rats that had received a high-sodium diet suggest that VIP may play a role in the increased bronchial reactivity reported with this diet.