Decreased hexokinase activity of the rat epididymal fat pad caused by high level of free fatty acids a possible factor in the mechanism of dietary adaptation

Abstract

1. 1. The increase in hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) activity of epididymal fat pads induced by glucose and insulin in vitro was inhibited by the addition of short-chain fatty acids to the incubation medium. The inhibitory effect tended to increase with the length of the hydrophobic chain. 2. 2. A transient elevation of tissue free fatty acids of epidymal fat pads incubated in vitro was established by successive additions of adrenalin and insulin to the incubation medium. This produced a biphasic effect on hexokinase activity, i.e. a small initial increase followed by a slowly established decreased activity level. It is indicated that this was the result of two effects on hexokinase activity, a positive effect of adrenalin which was counteracted by a negative effect of fatty acids. 3. 3. Fasting previously carbohydrated-fed rats resulted in decreased epididmal adipose tissue hexokinase activity and increased level of free fatty acids of the same tissue. 4. 4. The stability of adipose tissue hexokinase was decreased in the presence of octanoate. This is on line with the view that the fatty acids decrease the hexokinase activity level by increasing the degradation of the ezyme. 5. 5. The results give support to the suggestion that the increase in hexokinase activity induced by insulin may be mediated through the antilipolytic effect of this hormone.