Orally administered clonidine as a secretagogue of growth hormone and as a thymotrophic agent in dogs of various ages

Abstract

SUMMARY The growth hormone (gh) secretagogue activity of variable dosages of clonidine (16.5, 50, 150, and 450 μg/kg of body weight), given orally mixed with the daily food ration, was evaluated in young and old dogs. Significant (P < 0.05) increase in plasma gh concentration was detected at all dosages tested in young dogs and in response to all but the lowest dose tested in the old dogs fed the clonidine-containing diet. Old dogs had plasma gh concentration that exceeded that of young dogs when higher doses of clonidine were used. A clonidine (100 μg/kg)-supplemented diet was fed to middle-aged dogs twice daily for 30 days. Significant (P < 0.01) increase of plasma gh concentration was observed on the first day of the feeding trial, but was undetectable by day 30. After feeding the clonidine-enhanced diet for 30 days, the effects on thymic morphology were variable, and there was no effect on plasma thymulin titer. Clonidine-fed dogs had significantly increased lymphocyte blastogenic responsiveness to mitogens, compared with that of control dogs, when evaluated as stimulation index.