Variation in the endotoxin-induced ovine cortisol response and its association with immune function

A fundamental component of the stress response is the activation of the hypothalamic-pituitary-adrenal (HPA) axis and its downstream production of glucocorticoids such as cortisol. Previous work conducted in our laboratory identified high (H), middle (M) and low (L) cortisol responsive phenotypes in an out-bred sheep population using Escherichia coli endotoxin to induce acute inflammatory stress. The H and L phenotypes were found to have altered immune function compared to the M responders. The present study examined the F1-F3 generations to calculate the heritability of cortisol responsiveness, attempted to determine whether or not variation in this phenotype is due to HPA axis signalling, and if these phenotypes are associated with immune function: Cortisol phenotypes were found to be associated with antibody production and the cutaneous hypersensitivity response, but not innate immune function. Heritability was calculated to be 0.28 for the entire population (F0-F3). The role of signalling within the HPA axis could not be clearly confirmed.