Lymphocyte proliferative responses in neonatal pigs with high or low plasma cortisol concentration after stress induced by restraint.

Abstract

High plasma cortisol concentration is associated with perception of stress and reduced immune function in pigs. Neonatal pigs (12, 19, or 26 days old) were tested to determine maximal cortisol response to a mild restraint stressor. Pigs were fitted with indwelling jugular cannulas 4 days prior to restraint. One day before restraint, 10 ml of blood was removed for lymphocyte isolation and subsequent in vitro lymphocyte proliferation and interleukin 2 (IL-2) assays. On the day of restraint, blood samples were drawn 10 minutes before and 3, 10, and 20 minutes after holding each pig in a supine position for 1 minute. Plasma cortisol concentration was determined by use of radioimmunoassay. Pigs with maximal cortisol response greater than the mean value for that age group were classified in the high-responder (HIRES) group. Conversely, those with values lower than the mean maximal response were assigned to the low-responder (LORES) group. The HIRES pigs had larger relative adrenal gland weights and higher baseline and maximal cortisol responses, compared with LORES pigs (P = 0.0170, P = 0.0002, P = 0.0001, respectively). Mitogen-induced lymphocyte proliferative responses (to phytohemagglutinin, concanavalin A, and pokeweed mitogen) were 60% lower (P = 0.0037, P = 0.0432, P = 0.0103, respectively) in HIRES vs LORES pigs. In vitro IL-2 production did not differ between HIRES and LORES pigs.