Failure of norepinephrine to initiate procine malignant hyperthermia

Continuous intravenous infusion in pigs of norepinephrine, to blood concentrations of 140 ng.ml^–1, provided a test of the hypothesis that this sympathetic hormone can initiate malignant hyperthermia (MH). This study was performed during nitrous oxidepentobarbital anesthesia, and in part utilized sodium nitroprusside to maintain normal blood pressure and peripheral perfusion. Metabolic stimulation, or evidence of MH, did not occur in normal of susceptible pigs, as indicated by the lack of increase in both whole body O₂ consumption and arterial lactate concentration. Next, in contrast, susceptible pigs manifested MH when exposed to halothane and succinylcholine, while normal pigs did not. We conclude that norepinephrine does not mediate or initiate porcine whole body stress responses characteristic of MH.