Metabolic effects of hypopituitarism and acromegaly

Hypopituitarism is associated with reduced lean body mass and increased body fat, while in acromegaly the converse is true. Fasting plasma glucose is increased in acromegaly but fasting plasma insulin and C-peptide are increased in both groups. There is a positive association between fat mass and fasting serum insulin in hypopituitarism, suggesting insulin resistance. Hypoglycaemia unresponsiveness, rather than insulin sensitivity, is the feature of growth hormone deficiency. Basal metabolic rate (expressed per kg body weight) is increased in acromegaly and decreased in hypopituitarism but when expressed 'per kg lean body mass', is increased in both groups. There is a close correlation between fat mass and fasting free fatty acid and glycerol levels in obese but not normal weight patients with hypopituitarism; slim patients appear to metabolise and oxidise their fat stores more effectively than those who remain obese. Thus indirect evidence suggests that growth hormone has an important role in maintaining normal body composition and energy stores.