1. Six patients with panhypopituitarism and eight controls were studied before, during and after 30 min of moderate, steady exercise on a bicycle ergometer. Venous blood samples were taken for estimation of growth hormone, pyruvate, lactate, glucose, FFA, glycerol and ketone bodies.

2. Exercise caused a rise in serum growth hormone levels in control subjects and these fell to pre-exercise levels within 90 min. There was no change in the levels in the patients. The patients showed changes in blood metabolites resembling those of the controls. FFA levels were considerably elevated and post-exercise ketosis developed, these changes being more marked in the patients.

3. The differences in FFA and ketone bodies between patients and controls may be due to the lower levels of fitness in the patients. A further explanation may be that growth hormone depresses FFA levels after initial mobilization during exercise in normal subjects, but no such action can occur in patients with hypopituitarism.

4. It is concluded that growth hormone does not necessarily have a major role in fat mobilization or in the production of post-exercise ketosis. Thus, the lower levels of ketosis observed in athletes are not due to their lower levels of growth hormone.

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