Duration and magnitude of hypothalamic-pituitary-adrenal axis suppression caused by daily oral administration of a glucocorticoid was investigated, using an anti-inflammatory dose of prednisone. Twelve healthy adult male dogs were given prednisone orally for 35 days (0.55 mg/kg of body weight, q 12 h), and a control group of 6 dogs was given gelatin capsule vehicle. Plasma cortisol (baseline and 2-hour post-ACTH administration) and plasma ACTH and cortisol (baseline and 30-minutes post corticotropin-releasing hormone [CRH] administration) concentrations were monitored biweekly during and after the 35-day treatment period. Baseline plasma ACTH and cortisol and post-ACTH plasma cortisol concentrations were significantly (P < 0.05) reduced in treated vs control dogs after 14 days of oral prednisone administration. By day 28, baseline ACTH and cortisol concentrations remained significantly (P < 0.05) reduced and reserve function was markedly (P < 0.0001) reduced as evidenced by mean post-CRH ACTH, post-CRH cortisol, and post-ACTH cortisol concentrations in treated vs control dogs. Two weeks after termination of daily prednisone administration, significant difference between group means was not evident in baseline ACTH or cortisol values, post-CRH ACTH or cortisol values, or post-ACTH cortisol values, compared with values in controls. Results indicate complete hypothalamic-pituitary-adrenal axis recovery 2 weeks after oral administration of an anti-inflammatory regimen of prednisone given daily for 5 weeks.

The hypothalamic-pituitary-adrenocortical (HPA) axis was studied in 8 healthy cats after administration of supraphysiologic doses of methylprednisolone (MP). Ovine corticotropin-releasing hormone (oCRH) administration increased cortisol and adrenocorticotropic hormone (ACTH) concentrations. Significant (P < 0.05) suppression of cortisol and a trend toward suppression of ACTH was observed after 1 week of MP administration. The HPA axis quickly recovered from suppressive effects of MP 1 week after administration of the steroid was discontinued. Side effects of oCRH administration were minimal in 7 cats; however, 1 cat had a severe hypotensive reaction. Clinical abnormalities were not associated with MP administration. The HPA axis was suppressed by supraphysiologic doses of MP in all treated cats that lacked clinical signs consistent with iatrogenic HPA axis suppression. Despite the relatively active pars intermedia in cats, compared with human beings and dogs, feedback 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 concentrations was observed in 3 cats and possibly was related to the active pars intermedia in the cat.

The present study was undertaken to investigate the development of early embryos, the implantation rate in immature rats superovulated by transplantation of a pituitary gland. Thirty-day-old male rats were performed orchidectomy 15 days before removal of each pituitary orchidectomy 15 days before removal of each pituitary gland. A pituitary gland was transplanted under the right kidney capsule of 28-day-old female rat between 0700 and 1000h on the starting day of experiment which was designated as Day -2. Control rats were administered 4 IU PMSG at 1000 on day -2. Some of rats used to experiment were sacrificed to examine the changes of ovarian and uterine weights on days -2, -1, 0, 1, 2, 3 and 5. Other rats were sacrificed to recover the ova and observe the ovaries on Days 1, 2, 3 and 5. The implantation sites were counted on Days 8