ADRENOCORTICOTROPIC HORMONE AND CORTISOL CONCENTRATIONS AFTER CORTICOTROPIN-RELEASING HORMONE STIMULATION TESTING IN CATS ADMINISTERED METHYLPREDNISOLONE

The hypothalamic-pituitary-adrenocortical (HPA) axis was studied in 8 healthy cats after administration of supraphysiologic doses of methylp rednisolone (MP). Ovine corticotropin-releasing hormone (oCRH) adminis tration increased cortisol and adrenocorticotropic hormone (ACTH) conc entrations. Significant (P < 0.05) suppression of cortisol and a trend toward suppression of ACTH was observed after 1 week of MP administra tion The HPA axis quickly recovered from suppressive effects of MP 1 w eek after administration of the steroid was discontinued. Side effects of oCRH administration were minimal in 7 cats; however, 1 cat had a s evere hypotensive reaction. Clinical abnormalities were not associated with MP administration. The HPA axis was suppressed by supraphysiolog ic doses of MP in all treated cats that lacked clinical signs consiste nt with iatrogenic HPA axis suppression. Despite the relatively active pars intermedia in cats, compared with human beings and dogs, feedbac k of MP on the HPA axis resulted in similar trends in oCRH-stimulated ACTH and cortisol concentrations as observed in human beings and dogs. Lack of consistent correlation between ACTH and cortisol concentratio ns was observed in 3 cats and possibly was related to the active pars intermedia in the cat.