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; microliter/min; Na+ basal +19.8 +/- 7.2 to SP -23.2 +/- 7.5 microEq/min; Cl- basal 21.7 +/- 7.5 to SP -16.5 +/- 5.6 microEq/min). Under basal conditions, there was minimal secretion of potassium (-0.264 +/- 0.282 microEq/min); during SP infusion, K+ flux was altered to significant secretion (-1.784 +/- 0.271 microEq/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.
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