A dual challenge of corticotropin releasing hormone and vasopressin alters immune cell profiles in beef heifers
The duration and magnitude of cortisol release can have different effects on the immune response. Over the last decade, studies have suggested that acute stress, when cortisol is elevated for a short duration of time, can be immuno-stimulatory rather than immuno-suppressive. This study was designed to determine the effect of an induced cortisol release, via a dual corticotropin releasing hormone (CRH) and vasopressin (VP) challenge, on changes in immune cell profiles of beef heifers. Four d prior to the challenge, ten heifers (605 ± 13 kg) were fitted with indwelling jugular cannulas and indwelling vaginal temperature (VT) recording devices that measured VT continuously at 5-min intervals. On d 0, heifers were challenged i.v. with 0.3 µg/kg BW bovine CRH and 1.0 µg/kg BW bovine VP concurrently. Two, whole blood samples were collected at 30-min intervals from -2 to 8 h relative to the challenge at 0 h. One vacutainer containing EDTA was collected for complete blood cell count (CBC) analysis, and the second was collected in a 9-mL monovette serum tube. After collection, serum was isolated and stored at -80oC until analyzed for cortisol concentrations by ELISA. There was a time effect (P < 0.001) for VT, cortisol, and CBC variables. A multi-phasic response was observed for VT, with VT initially increasing (P = 0.05; relative to 0 h) within 15 min post-challenge. Serum cortisol concentrations increased (P < 0.001) immediately after the challenge, reaching maximum concentrations between 0.5 to 2 h post-challenge and then continually decreasing until reaching baseline concentrations at 6 h post-challenge (P = 0.17 for 0 h vs 6 h). Total white blood cell and lymphocyte concentrations increased (P < 0.001) 2 h after CRH/VP challenge, and remained elevated for the duration of the blood collection period. Monocyte concentrations initially decreased 1 h post-challenge (P < 0.001), and returned to baseline concentrations by 2 h post-challenge (P = 0.08 for 0 h vs 2 h). In contrast, neutrophil concentrations decreased (P = 0.02) 3 h post-challenge, and remained decreased throughout the duration of the blood collection period. These data demonstrate that immune cell populations are influenced by an acute activation of the hypothalamic-pituitary-adrenal axis. Additionally, the increase in circulating concentrations of lymphocytes and the decrease in circulating concentrations of neutrophils observed in this study are indicative of an immunological priming event that could be beneficial to the animal.
Keywords: acute stress, cortisol, immune response