Summary
We evaluated the effect of ovine corticotropin-releasing hormone (crh) on plasma immunoreactive (ir) concentrations of acth, α-melanocyte-stimulating hormone, and cortisol in 8 dogs with naturally acquired adrenocortical insufficiency. Of the 7 dogs with primary adrenal insufficiency, 6 had markedly high basal plasma ir-acth concentrations and exaggerated acth responses to crh administration, whereas 1 dog that was receiving replacement doses of prednisone at the time of testing had normal basal ir-acth concentrations and a nearly normal response to crh. In contrast, the 1 dog with secondary adrenocortical insufficiency had undetectable basal plasma ir-acth concentrations, which failed to increase after administration of crh. Basal plasma α-melanocyte-stimulating hormone concentrations in the dogs with adrenal insufficiency were within normal range and were unaffected by crh administration. In all 8 dogs with adrenal insufficiency, plasma cortisol concentrations were low and did not increase after administration of crh. Therefore, stimulation with crh produced 2 patterns of plasma ir-acth response when administered to dogs with naturally acquired adrenal insufficiency. Dogs with primary adrenal insufficiency had high basal plasma ir-acth concentrations and exaggerated responses to crh, whereas the dog with secondary adrenal insufficiency had undetectable basal plasma concentrations of ir-acth that did not increase after stimulation with crh.
