Histidine-imbalanced diets stimulate hepatic histidase gene expression in rats

A high protein concentration in the diet induces the gene expression of sev eral amino acid degrading enzymes such as histidase (Hal) in rats. It is im portant to understand whether the amino acid pattern of the dietary protein affects the gene expression of these enzymes. The purpose of the present w ork was to study the effect of a histidine-imbalanced diet on the activity and mRNA concentration of rat hepatic histidase. Seven groups of six rats w ere fed one of the following diets: 1) 6% casein (basal), 2) 20% casein, 3) 35% casein, 4) an imbalance diet containing 6% casein plus a mixture of in dispensable amino acids (IAA) equivalent to a 20% casein diet without histi dine (I-20), 5) 6% casein plus a mixture of IAA equivalent to a 35% casein diet without histidine (I-35), 6) a corrected diet containing 6% casein plu s IAA including histidine equivalent to a 20% casein diet, 7) a corrected d iet containing 6% casein plus IAA including histidine equivalent to a 35% c asein diet. Serum histidine concentration was inversely proportional to the protein content of the diet, and it was significantly higher in rats fed t he corrected diets compared to their respective imbalanced diet groups. Hat activity increased as the protein content of the diet increased. Greater h istidine imbalance resulted in lower food intake and higher Hal activity. R ats fed histidine-corrected diets had lower activity than their respective imbalanced groups. Differences in Hal activity were associated with differe nces in the concentration of Hal mRNA. These results indicate that rats fed a histidine-imbalanced diet exhibit reduced food intake and weight gain an d increased Hal gene expression as a consequence of an increased amino acid catabolism.