Plasma endogenous ACTH concentrations and plasma cortisol responses to synthetic ACTH and dexamethasone sodium phosphate in healthy cats

Plasma cortisol responses of 19 healthy cats to synthetic ACTH and dexamethasone sodium phosphate (DSP) were evaluated. After administration of 0.125 mg (n = 5) or 0.25 mg (n = 6) of synthetic ACTH, IM, mean plasma cortisol concentrations increased significantly (P less than 0.05) at 15 minutes, reached a peak at 30 minutes, and decreased progressively to base-line values by 120 minutes. There was no significant difference (P greater than 0.05) between responses resulting from the 2 dosage rates. After administration of 1 mg of DSP/kg of body weight, IV (n = 7), mean plasma cortisol concentrations decreased at postadministration hour (PAH) 1, and were significantly lower than control cortisol concentrations at PAH 4, 6, 8, 10, and 12 (P less than 0.01). Administration of 0.1 mg of DSP/kg, IV (n = 8) or 0.01 mg of DSP/kg, IV (n = 14) induced results that were similar, but less consistent than those after the 1 mg of DSP/kg dosage. Mean plasma cortisol concentrations returned to base-line values by PAH 24. There was not a significant difference between the 3 doses (P greater than 0.05) at most times. Measurement of endogenous ACTH in 16 healthy cats revealed plasma ACTH of less than 20 to 61 pg/ml. Seemingly, administration of synthetic ACTH consistently induced a significant (P less than 0.05) adrenocortical response in healthy cats. On the basis of time-response studies, post-ACTH stimulation cortisol samples should be collected at 30 minutes after ACTH administration to ensure detection of peak adrenocortical response.(ABSTRACT TRUNCATED AT 250 WORDS)