Restraint, but not frustration, induces prostaglandin-mediated hyperthermia in pigs

Three experiments were carried out to investigate stress hyperthermia in prepubertal pigs. Experiment 1 examined the effect of frustrative nonreward (psychological stress) on deep body temperature in animals (n = 7) trained to make operant responses for food following a 17.5-h period of deprivation. There was no change in body temperature when the feeders were switched off whereas there was a small increase (NS) during normal operant feeding that might be attributable to physical exertion. In Experiment 2, the effects of 15-min physical restraint (snaring) were examined in the same group of animals. This procedure induced a significant (p < 0.01) rise in core temperature that was completely abolished by prior administration of a cyclooxygenase inhibitor (indomethacin, 2 mg/kg given intravenously). The final experiment investigated the effects of snaring on plasma cortisol concentrations. Blood samples were taken from indwelling catheters in pigs (n = 5) subjected to 15-min restraint with, or without, indomethacin pretreatment. Snaring produced a significant (p < 0.001) increase in cortisol release that was not affected by the administration of indomethacin. These results suggest that snaring, a physical stress that may also have energy expenditure components, induces a prostaglandin-mediated hyperthermic response in the growing pig.