Salivary and plasma cortisol response to adrenocorticotropin administration in pigs

Two experiments were conducted to determine the responsiveness of salivary and plasma cortisol to acute (i.v.), depot (i.m.) and chronic (repeated i.m.) adrenocorticotropin (ACTH) administration in swine. In Experiment 1, barrows (castrated pigs) were assigned to one of three injection treatments: (1) saline i.m. (SHAM1 n = 2); (2) 0.75 IU/kg BW ACTH in saline i.v. (ACUTE, n = 2); (3) 2.25 IU/kg BW ACTH in gel i.m. (DEPOT, n = 3). Total cortisol concentrations were determined for concurrent saliva and blood samples. Correlations between salivary and plasma cortisol within treatments were: SHAM1, r = 0.60; ACUTE, r = 0.58; DEPOT, r = 0.79. In Experiment 2, barrows were assigned to one of two injection treatments: (1) gel i.m. (SHAM2, n = 3); (2) 2.25 IU/kg BW ACTH in gel i.m. (CHRONIC, n = 4). The injections occurred every 6 h for a total of eight injections. Concurrent saliva and blood samples were obtained every 3 h for 72 h followed by an increasing sampling interval until day 6. Overall correlations between salivary and plasma cortisol were: SHAM2, r = 0.30 and CHRONIC, r = 0.61. Experiment 1 found that the relationship between salivary and plasma cortisol was stronger during longer (DEPOT) than shorter (ACUTE) ACTH stimulation. Experiment 2 found a strong relationship between the two measurements during chronic ACTH stimulation, but that relationship weakened after ACTH stimulation ceased.