SOME HORMONAL, METABOLIC, AND NUTRITIONAL FACTORS INFLUENCING LIPID PEROXIDATION BY RAT ADIPOSE TISSUE IN VITRO*

Abstract

Rat adipose tissue incubated aerobically in vitro in a Krebs-Ringer bicarbonate medium with bovine serum albumin releases a substance which yields a chromogen when reacted with 2-thiobarbituric acid (TBA). The chromogen is presumed to represent the interaction of TBA with malonylaldehyde, a product of the peroxidation of polyunsaturated fatty acids. Adrenaline increases the production of the TBA chromogen. Provided there is no glucose in the medium, there is a high correlation between free fatty acid (FFA) and TBA chromogen release into the medium. When adipose tissue which has been stimulated to a high rate of lipolysis by adrenaline is incubated in a medium with a high concentration of glucose, FFA are eventually completely extracted from the medium, while the TBA chromogen progressively accumulates. These data suggest that the measurement of the products of peroxidation of unsaturated fatty acids may reflect lipolysis under conditions in which FFA values represent the net result of release and reutilization of fatty acids. Free fatty acid release by adipose tissue in vitro in response to adrenaline is reduced after hypophysectomy, but lipid peroxidation is disproportionately lowered. Incorporation of a-tocopherol into the chow diet of the normal rat lowers TBA chromogen production to that of the hypophysectomized rat, without altering FFA release. These data suggest a role for the pituitary in determining tocopherol requirements, and illustrate an application of the TBA reaction in adipose tissue to the study of vitamin E economy.