ON THE RESPONSE OF HEPATIC GLUCOSE-6-PHOSPHATE DEHYDROGENASE ACTIVITY TO CHANGES IN DIET COMPOSITION AND FOOD INTAKE PATTERN.

Abstract

1. 1.|Ethionine inhibition experiments suggest that the hepatic glucose-6-phosphate dehydrogenase increase seen on refeeding and after fructose feeding probably represents de novo protein synthesis. Some difficulties in interpreting experiments done with protein synthesis inhibiting maneuvers in whole animals are discussed. 2. 2.|No increase in glucose-6-phosphate concentration of liver is detectable before or during periods of rapid dehydrogenase activity increase. 3. 3.|Inhibition of lipogenesis by the isocaloric substitution of fat for protein in a high glucose diet is accompanied by failure of enhancement of glucose-6-phosphate dehydrogenase activity. When the enzyme level has been elevated as a result of carbohydrate feeding the addition of fat to the diet results in a lowering of enzyme activity but only after a 2 day latent period. 4. 4.|The administration of 2 ml of corn oil by stomach tube to carbohydrate diet adapted rats has the following effects within 2 hr (a) decreased lipogenesis from glucose and acetate and (b) decreased appearance of glucose carbon 1 in CO2. These findings suggest that inhibition of lipogenesis results in a dimunition of glucose-6-phosphate oxidation by way of the pentose pathway. 5. 5.|A number of treatments (methylene blue, menadione and phenobarbital administration) designed to increase cellular demand for NADPH2 were without effect on glucose-6-phosphate dehydrogenase activity. An attempt to increase tissue NADP concentration by nicotinamide feeding was similarly without effect.