Metabolic Rate and Blood Hormone and Metabolite Levels of Individuals Susceptible to Malignant Hyperpyrexia at Rest and in Response to Food and Mild Exercise

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Abstract
Resting metabolic rate and energy cost of performing a specific (light) work load on a bicycle ergometer were measured in 9 subjects susceptible to malignant hyperpyrexia (MHS) and 9 controls, fasting and following a 600-kcal meal. Blood glucose, lactate, pyruvate and serum triglycerides, thyroxine, cortisol, creatine kinase, growth hormone and Ca and K levels at rest and immediately following exercise, after fasting and eating, were measured. There was no evidence of increased heat production in MHS subjects compared with controls. MHS subjects showed an absence of dietary-induced thermogenesis with exercise. Compared with the controls, MHS subjects had higher insulin levels for essentially the same blood glucose values. Triglycerides in the MHS group rose steadily over the course of the experiment; in controls they did not vary from initial value. Lactate did not rise as much with exercise in the MHS group but did not fall with rest, and pyruvate did not change from resting fasting values; in controls it rose steadily. Differences were also found in thyroxine and cortisol levels between MHS and controls. The shunting of blood away from thermogenic tissue was suggested as a mechanism for the absence of diet-induced thermogenesis with exercise in the MHS group and the possibility of an underlying abnormality of cardiovascular (sympathetic) control mechanisms in these subjects was discussed. Biochemical abnormalities were discussed in relation to previous biochemical data from MHS humans and pigs and in relation to the abolition of dietary-induced thermogenesis.