Suppression of growth hormone secretion in spontaneous canine hyperadrenocorticism and its reversal after treatment

The plasma growth hormone response to the provocative agent, xylazine, was assessed in 4 dogs with spontaneous hyperadrenocorticism, before and after therapy. Before treatment of the hyperadrenocorticism, no significant increase in growth hormone concentration occurred in any of the dogs following the administration of xylazine. A significant increase in growth hormone concentrations following xylazine administration occurred in 2 of the 3 dogs with hypophysis (pituitary)-dependent hyperadrenocorticism after treatment with mitotane (o,p'-DDD) and in 1 dog after surgical removal of a hyperfunctional adrenal adenoma. Although the impaired growth hormone response persisted in 1 dog, the administration of xylazine was repeated in this animal after only 3 weeks of mitotane therapy; it is likely that growth hormone unresponsiveness would reverse if the hyperadrenocorticism were controlled for a longer period. These findings demonstrate that in dogs, as in persons, the excessive production of endogenous corticosteroids associated with either hypophysis-dependent hyperadrenocorticism or hyperfunctional adrenal tumor can induce suppression of growth hormone release which is reversible following treatment.