A FAT-MOBILIZING FACTOR IN RAT SERUM

Abstract

ABSTRACT The serum of rats promoted triglyceride breakdown in isolated adipose tissue cells incubated in vitro, as shown by increased glycerol release into the medium. The serum of fed rats had a smaller fat-mobilizing action than that of rats fasted for 20 h. There was a very close linear relation of dose-response versus dose, as occurs in other physiological responses provoked by a hormone acting on a limited number of receptors. The maximum lipolytic effect of serum from fasted animals was of the same order as the maximum effect of noradrenaline, and amounted to a breakdown of about 1.5% of the adipose cell triglyceride per hour. The triglyceride breakdown provoked by serum was inhibited by the β-blocking drug propranolol, but was not affected by insulin even in high concentration.