Serotoninergic control of growth hormone (GH) secretion in dogs as measured by dose responsiveness

L-5-hydroxytryptophan (5-HTP) - induced GH release has been demonstrated in animals and man, but serotoninergic control remains controversial. We developed a sensitive radioimmuno-assay for measurement of canine GH and investigated the 5-HTP dose-response relationship in unanesthetized mongrel bitches. Intravenous administration of 1, 5, 10, and 25 mg/kg doses of 5-HTP caused GH release but an increased latency in peak GH response was seen with the larger doses. Doses of 10 and 25 mg/kg induced stressful behavior and markedly increased plasma corticoid levels while lower doses were without effect. From these findings in the dog we conclude that the GH response to low dose 5-HTP is not due to stress and that alternate mechanisms are needed to explain the variable serotoninergic control of GH release demonstrated with low and high dose 5-HTP stimulation.