Patterns of dietary and hormonal induction of certain NADP-linked liver enzymes

Abstract

Estrogen and thyroxine induction of hepatic hexosemonophosphate shunt and NADP-linked malic dehydrogenases was studied in rats on chow and on a high-fat, low-carbohydrate diet. A different enzyme pattern resulted from treatment with each of the hormones; i.e., estrogen produced a greater effect on the dehydrogenases of the pentose phosphate pathway while thyroxine showed a greater influence on the malic enzyme. Both enzymes were inducible in animals adapted to a high-fat diet, suggesting that accelerated glucose absorption from the gastrointestinal tract is not an essential feature of the mechanism of hormonal induction. However, in the case of the shunt enzymes, availability of dietary carbohydrate resulted in greater increases in enzyme activity than did induction on a high-fat diet. Refeeding a high-carbohydrate diet after a 48-hr fast resulted in a simultaneous increase in both shunt dehydrogenases and malic enzyme, a fact which disproves the hypothesis that the adaptive increase of the former is secondary to a primary increase in the latter.