Carbohydrate synthesis in the isolated perfused rat liver: role of the adrenal cortex

Glycogen synthesis in the perfused liver of adrenalectomized rats

1. A total loss of capacity for net glycogen synthesis was observed in experiments with the perfused liver of starved adrenalectomized rats. 2. This lesion was corrected by insulin or cortisol in vivo (over 2-5h), but not by any agent tested in perfusion. 3. The activity of glycogen synthetase a, and its increase during perfusion, in the presence of glucose plus glucogenic substrates, were proportional to the rate of net glycogen accumulation. 4. This complete inherent loss of capacity for glycogen synthesis after adrenalectomy is greater than any defect in hepatic metabolism yet reported in this situation, and is not explicable by a decrease in the rate of gluconegenesis (which supports glycogen synthesis in the liver of starved rats). The short-term (2-5h) stimulatory effect of glucocorticoids in the intact animal, on hepatic glycogen deposition, may be mediated partly through insulin action, although neither insulin or cortisol appear to act directly on the liver to stimulate glycogen synthesis.

Influence of glucocorticoids on glucagon secretion and plasma amino acid concentrations in man

Plasma concentrations of glucagon, insulin, glucose, and individual plasma amino acids were measured in normal nonobese and obese subjects before and after 3 days of dexamethasone treatment (2 mg/day) and in patients with Cushing's syndrome. The subjects were studied in the basal postabsorptive state and following the infusion of alanine (0.15 g/kg) or ingestion of a protein meal. In nonobese subjects dexamethasone treatment resulted in a 55% increment in basal glucagon levels and in a 60-100% increase in the maximal glucagon response to alanine infusion or protein ingestion. In obese subjects, basal glucagon rose by 110% following dexamethasone, while the response to alanine increased fourfold. In patients with Cushing's syndrome basal glucagon levels were 100% higher and the glucagon response to alanine infusion was 170% greater than in normal controls.Dexamethasone treatment in normal subjects resulted in a 40% rise in plasma alanine concentration which was directly proportional to the rise in basal glucagon. The remaining 14 amino acids were unchanged. In the patients with Cushing's syndrome alanine levels were 40% higher than in normal controls and were directly proportional to basal glucagon concentrations. No other plasma amino acids were significantly altered in the group with Cushing's syndrome. It is concluded that (a) glucocorticoids increase plasma glucagon concentration in the basal state and in response to protein ingestion or aminogenic stimulation; (b) this effect of glucocorticoids occurs in the face of obesity and persists in chronic hypercorticism; (c) hyperalaninemia is a characteristic of acute and chronic glucocorticoid excess, and may in turn contribute to steroid-induced hyperglucagonemia; and (d) increased alpha cell secretion may be a contributory factor in the gluconeogenic and diabetogenic effects of glucocorticoids.