Enhanced fluid intake by rats after capsaicin treatment.

These studies examined stimulated fluid intake by rats in which vagally mediated signals of gastric distension were blunted by systemic treatment with the neurotoxin capsaicin, as verified by the loss of cholecystokinin-induced inhibition of feeding. After overnight food deprivation, intake of a 10% sucrose solution by capsaicin-treated rats was greater than that by control rats. Similarly, capsaicin-treated rats drank more water than did control rats when stimulated by plasma hyperosmolality after intraperitoneal administration of hypertonic NaCl or by isosmotic hypovolemia after subcutaneous administration of a hyperoncotic colloidal solution. Finally, during chronic administration of the mineralocorticoid deoxycorticosterone acetate, capsaicin-treated rats consumed more concentrated saline than did control rats. In all tests, intakes by capsaicin-treated rats were significantly greater than those by control rats within 5-15 min. These results suggest that early signals of gastric distension, such as those that occur during normal episodes of food, water, or NaCl intake, may modulate ongoing ingestion and that, with the attenuation of such general inhibitory signals, ingestion continues until gastric distension becomes larger and/or later postgastric signals are detected.