Effect of hypothalamic preparations on human omental adipose tissue in vitro

Abstract

The lipolytic responses of rat and human adipose tissue to several pituitary hormones, catecholamines, and purified preparations from human and porcine hypothalami have been compared. Fragments of human omental adipose tissue, obtained at surgery, or rat epididymal adipose tissue were incubated in vitro for 2 hr in 2 ml of Krebs-Ringer bicarbonate medium containing 3% bovine albumin. Acetic acid extracts of human and porcine stalk median eminence tissue were purified by gel filtration on Sephadex G-25. Lipid-mobilizing factor (LMF) activity emerged in an area occupied by peptides with a molecular weight of 3000–5000. This lipolytic fraction was found to be free of thyroid-stimulating hormone (TSH) and catecholamines. The ACTH content of this fraction was found to be less than 10 mU/mg. Addition of 20–60 μg/ml of porcine or human LMF to the medium significantly increased lipolysis, as measured by glycerol release into the medium, from human and rat adipose tissue. Human LMF elicited a greated lipolytic response in human omental adipose tissue than did the procine LMF, but porcine LMF was more potent in rat epididymal adipose tissue. This suggests that a species specificity may exist for the lipolytic activity of hypothalamic lipid mobilizers. Responsiveness of human omental adipose tissue to adrenalin was lower than that of rat epididymal adipose tissue. Addition of corticotropin A (10–20 μg/ml), human growth hormone (10–30 μg/ml), and alpha or beta melanocyte-stimulating hormone (MSH) (10–30 μg/ml) had no effect on lipolysis when incubated with human omental adipose tissue. However, the addition of 1.5–3.0 mU/ml of human TSH significantly increased the release of glycerol from human omental adipose tissue. These data suggest that human hypothalamic extracts, like those of porcine hypothalamic extracts, contain a lipid-mobilizing factor or factors that may differ chemically from corticotropin, TSH, growth hormone, and the catecholamines.