Salivary responses to an experimental activation of the HPA axis in pigs: Effects of ACTH on analytes related to stress, immune system, inflammation, redox status and metabolism

Non-invasive biomarkers are essential for assessing stress and welfare. Saliva is a suitable sample type because it can reflect endocrine, immune, inflammatory and redox responses without causing stress from handling. This study examined the impact of administering adrenocorticotropic hormone (ACTH) on a broad range of salivary analytes in pigs, to characterise the physiological response of saliva to the activation of the hypothalamic-pituitary-adrenal (HPA) axis. A total of twenty-two male Landrace x Large White pigs were randomly assigned to receive either ACTH (10 µg/kg; n = 11) or saline solution (n = 11). Saliva samples were collected before and after injection (at 20, 40, 60, 90 and 120 min, and after 24 h) and analysed for biomarkers of stress (cortisol, cortisone, chromogranin A, alpha-amylase, total esterase activity, butyrylcholinesterase and oxytocin), inflammation (haptoglobin, C-reactive protein and calprotectin), immunity (adenosine deaminase and total proteins), redox status (cupric reducing antioxidant capacity), and metabolism (urea and creatinine). ACTH administration induced significant increases in cortisol, cortisone, and total esterase activity, confirming HPA axis activation. However analytes related to sympathetic activation (chromogranin A and alpha-amylase) or positive welfare (oxytocin) remained unchanged. Regarding inflammatory markers, haptoglobin and calprotectin, but not C-reactive protein, increased. No significant changes were observed in redox and metabolism biomarkers. These data contribute to a better understanding of the physiological response of saliva components to ACTH administration, which is one of the major mechanisms involved in acute stress.