Regulation of histidase gene expression by glucagon, hydrocortisone and protein-free/high carbohydrate diet in the rat

Abstract

The effect of glucagon and hydrocortisone was investigated to understand the mechanism of induction of hepatic histidase gene. In this study, glucagon (0.6 mg 100 g body wt d ) was injected to rats fed 10% casein diet. After 3h of the last injection, histidase activity and amount of enzyme were induced by 3 fold and histidase mRNA concentration by 6 fold. Injection of hydrocortisone (2 mg 100g body wt d ) increased 100% histidase activity and mRNA concentration and by 150% the amount of enzyme after 3 h of the last injection. These results indicate that glucagon is a better inductor of histidase gene expression than hydrocortisone. Another purpose of the study was to evaluate if a protein-free/high carbohydrate diet could reverse the induction of Hal expression produced by a high protein diet. Hal activity, amount of enzyme and mRNA concentration was repressed by 68, 88 and 95% respectively by a protein-free/high carbohydrate diet. Injection of glucagon reversed partially the effect of a high carbohydrate diet, however, injection of hydrocortisone under the concentration used in these experiments did not reverse the effect of a high carbohydrate diet. These results support the evidence that hepatic histidase gene expression is probably regulated transcriptionally by hormones.