Response of plasma and salivary cortisol to the administration of single or multiple injections of ACTH in barrows

Abstract

Two experiments were designed to determine if salivary cortisol can be used instead of total plasma cortisol measurements in pigs. In Exp. I., seven barrows averaging I I wk and 25 kg were assigned to the following treatments: (1) 2.25 fU/kg BW adrenocorticotropin (ACTH) in gel injected i.m (ACTH-G); (2).75 IU/kg BW ACTH in saline injected i.v. (ACTH-S); (3) saline injected i.m. (SAL). Concurrent blood and saliva samples were obtained at-.33 , 0, .33, .66, 1, 1.5, 2, 3, 5, 7, 10, 14, 24, 31, 38, and 48 h. In Exp. 2., seven barrows averaging 10 wk and 15 kg were assigned to two treatments of 8 injections every 6 h for 48 h of-. (1) 2.25 IU/kg BW ACTH in gel injected i.m. (ACTH-G)-, or (2) gel carrier injected i.m. (GEL). Concurrent blood and saliva samples were obtained at-.33, 0, I and then every 3 h until 72 h, after which samples were obtained at 78, 84, 96, 99, 108, and 120 h. In Exp. 1, salivary cortisol increased and the pattern of salivary cortisol mimicked that of total plasma for ACTH-G, but not ACTH-S barrows. Plasma cortisol area under the curve (AUC) for ACTH-G and ACTH-S differed (P=.0052), whereas salivary AUC's for these treatments did not differ (P=.26). Correlations between total plasma and salivary cortisol were: SAL, r--.60, P=.0023; ACTH-G, r--.79, P=.OOOI; ACTH-S, r--.58, P=.OOI 1. In Exp. 2, salivary cortisol had similar peaks over the 45 h of injections compared to plasma cortisol where injection peaks decreased. After ACTH injections ceased, total plasma cortisol for ACTH-G remained at low concentrations for 36 h following the last injection indicating a disruption in normal daily rhythms which did not occur in salivary cortisol. This difference in salivary and total plasma cortisol in both Exp. I and Exp. 2 indicates that there is not a direct consistent relationship between salivary and total plasma cortisol. However, if salivary cortisol reflects unbound cortisol as it does in humans, then this difference may be important to researchers interested in the changes in the biologically-active fraction of circulating cortisol concentrations.