Abstract
Mouse epididymal fat pads were incubated for 2 hours in 3 per cent albumin Krebs-Ringer phosphate buffer (KRP), free of calcium and glucose, or in Krebs-Ringer bicarbonate (KRB) containing calcium. Addition of defatted acetic acid extracts of pituitary stalk and median eminence (SME) of ovine, porcine, bovine and human orgin significantly increased lipolysis as measured by release of glycerol into the KRP incubation medium and inhibited 1-
14C acetate incorporation into lipids. Extracts of porcine SME were the most potent in enhancing glycerol release and showed a log-dose response relationship between 0.1 mg. to 1.0 mg. extract/ml. of medium. Extracts of cerebral cortex from all the species tested were without effect on lipolysis at these dose levels. After gel filtration of porcine SME extracts on Sephadex G-25, lipolytic activity emerged in an area occupied by peptides with molecular weight of 3000 to 5000. The same area contained ACTH-like activity (200 mU./mg.). A comparison of the in vitro lipolytic activity of this hypothalamic fraction indicated that it was active in doses as small as 20 μg./ml. when incubated in KRP with mouse, rat, and hamster fat pads. Higher doses (40 μg./ml.) were required to elicit a lipolytic response from rabbit and guinea pig tissue. Incubation of the hypothalamic fraction with trypsin and chymotrypsin abolished the lipolytic response while pepsin had no effect. Chemical analyses of this hypothalamic fraction showed it to be free of calcium and norepinephrine and its lipolytic activity could not be accounted for by contamination with TSH, oxytocin, vasopressin, α and β-MSH or hypothalamic releasing factors. Most, but not all, of the lipid mobilizing activity of the porcine fraction may be accounted for by ACTH and/or its analogues with adrenocorticotropic activity.
