EFFECT OF FASTING ON THE ADRENERGIC-RECEPTOR ACTIVITY OF HUMAN ADIPOCYTES

Abstract

To assess the influence of fasting on the .alpha.- and .beta.-adrenergic receptor activities of human adipocytes, subcutaneous adipose tissue was obtained from normal obese subjects in the fed state and after 3 days of fasting. Isolated cells prepared from the adipose tissue were incubated with epinephrine (10-6 M) and in the presence of the .alpha.-blocker phentolamine (10-5 M) and the .beta.-blocker propranolol (10-5 M), respectively. Intracellular cyclic[c]AMP levels and glycerol released into the buffer were measured. Epinephrine stimulated cAMP and glycerol release when incubated with cells from fed subjects. Phentolamine enhanced this action and propranolol reduced it below the basal level. Epinephrine suppressed cAMP and lipolysis when incubated with adipocytes from fasted individuals. This reversal in the effect of epinephrine on adipocytes apparently is due to a reduction in .beta.-receptor activity rather than an increase in .alpha.-activity. This change in .alpha.- and .beta.-adrenergic receptor balance apparently occurred after 1 day of fasting and was not significantly exaggerated when fasting was prolonged to 8 days. In the fasting state the sympathetic nervous system and circulating catecholamines act to conserve adipose tissue triglyceride.