Effect of Serotonin on Gastric Secretion in the Dog

ABSTRACT

Heidenhain pouch secretion in response to small dose of serotonin was studied in conscious dogs. A single subcutaneous injection of 0.5 to 2.0 mg of serotonin produced no changes in spontaneous fasting secretion; however, the milk-induced secretion was greatly inhibited by the same dose. This inhibition was abolished by treatment of dibenzyline or LSD(d-lysergic acid die- thylamide). LSD alone enhanced the response of gastric secretion to milk. Constant intravenous infusion of serotonin, at levels of 3 to 10 microgram/kg/min was associated with a significant increase in the volume of gastric juice aspirated from three anesthetized dogs, but the acidity of juice varied very slightly. However, when histamine is given as much as 0.8 to 3 microgram/kg/min, a marked increase in both the volume and acidity was observed. A significant elevation of mucin content in the juice obtained from the Heidenhain pouch was seen in dogs receiving a single subcutaneous injection of 1.0 mg of serotonin. In case of histamine, the mucin content of pouch juice was not relatively increased and merely an increase in the total amount of mucin secondary to the volume increase was seen. The observed increase in mucin by serotonin was inhibited by LSD, BOL (2-bromo-d-lysergic acid diethylamide) or dibenzyline, and mildly by morphine. Atropine or hexamethonium did not block the response of mucin production to serotonin. The gastrointestinal motility elicited by serotonin was not affected by these agents. It is felt that the receptor(s) responsible for the mucin production in the dog belongs to the D-receptor types postulated by Gaddum and Picarelli.