Serotonergic Regulation of Cortisol Secretion in Dogs

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Abstract
The role of serotonin (5-HT) in the control of serum cortisol secretion was studied in 50 conscious beagle dogs. A significant rise in corticosteroids was observed after 1.5 and 3 mg/kg (P < 0.01) i.v. fenfluramine, an indirect serotonergic agonist, as well as after 2 (P < 0.05) and 3 mg/kg (P < 0.01) i.v. quipazine, a direct agonist of 5-HT receptors. Both drugs exhibited a dose-related effect. A lower dose of fenfluramine, 0.5 mg/kg, was ineffective when administered i.v. but raised serum corticol (P < 0.05) after direct injection into a lateral cerebral ventricle, through a chronically implanted brain cannula. The marked increases in corticosteroid concentration produced by the highest fenfluramine and quipazine doses were completely abolished by pretreatment with ketanserin, an antagonist of 5-HT2 receptors, which did not affect cortisol secretion when administered alone. The brain serotonergic system may play a role in the control of cortisol secretion in conscious dogs.