Substance P-induced intestinal secretion of water and electrolytes

This study was initiated to determine if raised (carcinoid) plasma concentrations of substance P induced jejunal secretion of water and electrolytes. Five dogs had isolated and cannulated 25 cm jejunal segments perfused at 2 ml/min with a neutral, isotonic perfusate. Saline, 1.0 ml, was infused intravenously during basal and recovery periods, while substance P was administered intravenously at 75 ng/kg/min (55 pmol/kg/min) during the four 15 minute experimental periods. Infusion increased plasma SP concentrations from basal (5.8 ± 1.3 pg/ml) to a mean plateau level of 121.2 ± 25.2 pg/ml (mean ± SEM). During SP infusion, intestinal secretion of water, Na⁺, and Cl^- were documented (H₂O basal +102 ± 60 to SP -275 ± 60; μl/min; Na⁺ basal +19.8 ± 7.2 to SP -23.2 ± 7.5 μEq/min; Cl^- basal 21.7 ± 7.5 to SP -16.5 ± 5.6 μEq/min). Under basal conditions, there was minimal secretion of potassium (-0.264 ± 0.282 μEq/min); during SP infusion, K⁺ flux was altered to significant secretion (-1.784 ± 0.271 μEq/min). Serum concentrations of Na and Cl were unchanged during SP infusion, but serum potassium concentrations fell from 4.64 ± 0.12 to 3.85 ± 0.40 mEq/l. The data demonstrate that substance P at levels noted in the carcinoid syndrome induces significant jejunal secretion of water and electrolytes in the dog.