Plasma immunoreactive proopiomelanocortin peptides and cortisol in normal dogs and dogs with Addison's disease and Cushing's syndrome: basal concentrations.
We measured basal plasma concentrations of the immunoreactive (IR) proopiomelanocortin (POMC)-derived peptides ACTH, beta-lipotropin (beta LPH), beta-endorphin (beta END), and alpha MSH in 160 normal dogs, 32 dogs with Addison's disease, 42 dogs with adrenocortical tumors causing Cushing's syndrome, and 169 dogs with pituitary-dependent Cushing's disease. In normal dogs, plasma IR-POMC peptide levels were similar to those in man, except that IR-alpha MSH, a pars intermedia POMC product, was readily detected. In Addisonian dogs, plasma cortisol was decreased, and the IR-POMC peptides were increased, except for IR-alpha MSH, which was normal. In 7 Addisonian dogs given dexamethasone, elevated plasma IR-ACTH, beta LPH, and beta END levels fell dramatically. In dogs with Cushing's syndrome due to adrenal tumors, plasma IR-ACTH, beta LPH, and beta END were decreased, and cortisol was increased, but IR-alpha MSH was normal. Dogs with Cushing's disease due to pars distalis tumors had elevated plasma IR-ACTH, beta LPH, beta END, and cortisol, but normal IR-alpha MSH; their plasma cortisol was suppressed by dexamethasone. There appeared to be 2 types of pars intermedia tumors causing Cushing's disease: 1 dexamethasone nonsuppressible and with disproportionately high plasma IR-alpha MSH levels, the other relatively dexamethasone suppressible and with normal to slightly elevated IR-alpha MSH levels. These 2 pars intermedia tumor types may arise from 2 distinct normal canine pars intermedia cell types. Canine Cushing's disease may provide a useful model for variants of the disorder in man.
D000224:Addison Disease / Q000097:blood*; D000236:Adenoma / Q000097:blood; D000310:Adrenal Gland Neoplasms / Q000097:blood; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D003480:Cushing Syndrome / Q000097:blood*; D003907:Dexamethasone / Q000494:pharmacology; D004195:Disease Models, Animal; D004285:Dogs; D004723:Endorphins / Q000097:blood; D005260:Female; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000097:blood; D010908:Pituitary Hormones, Anterior / Q000097:blood*; D010911:Pituitary Neoplasms / Q000097:blood; D001615:beta-Endorphin; D008083:beta-Lipotropin / Q000097:blood
D004723:Endorphins; D010908:Pituitary Hormones, Anterior; D001615:beta-Endorphin; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D009074:Melanocyte-Stimulating Hormones; D008083:beta-Lipotropin; D006854:Hydrocortisone