Porcine muscle responses to carbachol, alpha‐ and beta‐adrenoceptor agonists, halothane or hyperthermia.

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Abstract
Whole body trans-section at the level of the 1st or 2nd lumbar vertebra of stress-susceptible or normal Poland China swine provided a preparation of isolated perfused caudal muscle that was without nervous or hormonal influences. Metabolic responses to halothane anesthesia were exaggerated in the susceptible preparation. Carbachol (10-4 M) increased O2 consumption 3-fold and elevated blood lactate levels from 3-8 .mu.mol/ml in susceptible but not in normal muscle preparations. Isoprenaline in a continuous infusion (2.5 .mu.g/kg caudal wt per min for 12 min, subsequently diminished to 1.2 .mu.g/kg per min) did not increase O2 consumption of susceptible or normal muscle, but did increase blood lactate by 2 .mu.mol/ml in both. Simultaneous administration of carbachol and isoprenaline resulted in additive increases in blood lactate. Incremental increases in temperature > 41.degree. C initiated exaggerated increases in O2 consumption and blood lactate in susceptible but not normal muscle; these were similar to whole body responses. Phenylephrine (0.2-25 .mu.g/kg per min continuous) produced hypertension, no observed effects upon aerobic or anaerobic metabolism and progressive tissue edema; these effects were similar in susceptible and normal muscle. Skeletal muscle from stress-susceptible swine is evidently inherently capable of metabolic responses to cholinergic agonists and increased temperature; these responses are greater than those in normal muscle. Initiation of stress responses in intact swine is related to somatic motor and sympathetic stimulation of abnormal skeletal muscle, and not to a somatic or sympathetic nervous system disorder.

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