Metabolic rate and blood hormone and metabolite levels of individuals susceptible to malignant hyperpyrexia at rest and in response to food and mild exercise.

Resting metabolic rate and the energy cost of performing a specific (light work load on a bicycle ergometer were measured in nine subjects susceptible to malignant hyperpyrexia (MHS) and nine control subjects, both fasting and following a 600-kcal meal. Blood glucose, lactate, pyruvate and serum triglycerides, thyroxine, cortisol, creatine kinase, growth hormone, and calcium and potassium levels at rest and immediately following exercise, after fasting and eating, were measured. There was no evidence of increased heat production in the MHS subjects compared with controls. The MHS subjects, however, showed a complete 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, whereas in the controls they did not vary from the initial value. Lactate did not rise as much with exercise in the MHS group but did nor fall with rest, and pyruvate did not change from resting fasting values, whereas in the controls it rose steadily. Differences were also found in thyroxine and cortisol levels between the MHS and control groups. The shunting of blood away from thermogenic tissue is 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 is discussed. The biochemical abnormalities are discussed in relation to previous biochemical data from MHS humans and pigs and in relation to the abolition of dietary-induced thermogenesis.