MALIGNANT HYPERTHERMIA IN THE PIG AND THE ROLE OF STRESS *

Malignant hyperthermia (MH) is a paradoxical response to certain anesthetic drugs in which muscle is stimulated sufficiently to produce a fatal hypermetabolic response, with a consequent rise in body temperature. Porcine MH occurs most often in breeds and strains of pigs that are known to be susceptible to a variety of different forms of stress, including transport, fighting, restraint, and hot weather; under these conditions, they develop tachycardia, tachypnea. cyanosis, increase in muscle tone, and high temperature. Many die from the porcine stress syndrome, which accounts for a substantial economic loss to the pig industry.' In addition, stress-susceptible pigs produce poor-quality meat, with an increased loss of water that spoils the appearance in the shop and also represents a serious economic loss.? The rapidity of muscle glycolysis, more specificially, the mechanisms responsible for triggering it, provides a link among the problems of poor meat quality, stress susceptibility, and MH in pigs. In man, MH is a rare but often fatal sequel of anesthesia that usually occurs quite unexpectedly in apparently healthy * The true incidence in man is not known, and because little information can be collected at the time of the crises, the picture of human MH is still confused and not well understood. The information that has been gathered suggests that the syndrome is essentially the same in man as in susceptible breeds of pigs. The fact that the syndrome can be produced more or less to order in pigs explains why much more is known about many aspects of porcine MH than of human MH. For these several reasons, porcine MH has become a valuable model system in which the biochemical changes that occur during stress and slaughter can be studied in the intact animal under laboratory conditions. In addition, although the difficulties involved in extending conclusions from experiments in one species to a clinical syndrome in another are appreciated, results from studies performed