REPEATED RESTRAINT AND ISOLATION STRESS IN LAMBS INCREASES PITUITARY-ADRENAL SECRETIONS AND REDUCES CELL-MEDIATED-IMMUNITY

Rambouillet crossbred ewe lambs were used to evaluate the effect of repeated restraint and isolation stress (RIS) on endocrinological and immunological functions. Lambs were blocked by weight and assigned to either RIS (n = 6) or to control (CON; n = 6) treatments. All lambs were tethered in environmentally controlled rooms at 22-degrees-C with constant light and, at this time (d 0), were given 1 mg of ovalbumin in adjuvant. On d 12, catheters were placed nonsurgically into the jugular vein of all lambs, and they were reimmunized with .5 mg of ovalbumin in incomplete adjuvant. Each lamb in the RIS treatment group was removed from its home stanchion, isolated from visual and tactile (but not auditory and olfactory) contact with other lambs, and restrained for 6 h on d 14, 15, and 16. Lambs in CON treatment remained undisturbed in their home stanchions. Lymphocyte blastogenic function and production of interleukin-2 (IL-2) were assessed in samples of blood collected before and at the conclusion (0 and 6 h) of each of the three stress bouts. In addition, ACTH and cortisol secretion in response to RIS was evaluated in samples of plasma and serum collected at .5-h intervals on the first and last days of stress (d 14 and 16). Finally, antibody production in response to immunization against ovalbumin was assessed in samples of serum obtained 14 d after reimmunization on d 12 of the study. Polynomial curves fit to the ACTH and cortisol data differed (P < .005) on both d 14 and 16 between RIS and CON treatments. The area under the cortisol response curve in RIS lambs was reduced (P < .001) on d 16 compared with d 14, whereas the area under the ACTH response curve was not different between these 2 d. Lymphocyte blastogenic response to pokeweed mitogen was not affected by treatment. However, blastogenic response to phytohemagglutinin was lower (P < .005) in RIS lambs at the conclusion of each stress bout on d 14, 15, and 16 and even before the onset of stress on d 16 (P < .05). Blastogenic response also was reduced (P < .005) in response to concanavalin A at 6 h on d 15 and 16. No day x treatment interaction was noted for production of IL-2, but, overall, production of IL-2 by RIS lambs was reduced (P < .001). Antibody response to ovalbumin was not influenced by treatment. The data suggest that repeated application of a stressor repeatedly activates the pituitary-adrenal system and reduces some measures of cell-mediated immunological function.