Differential effects of protein restriction on gamma-glutamyltranspeptidase [EC 2.3.2.2] activity in young and mature rats

Gamma-glutamyltranspeptidase (GGT, EC 2.3.2.2) activity was determined in the plasma and liver of 40 young (50 days old) and 40 mature (300 days old) male Wistar rats, after a protein restriction period of 28 days. Casein protein levels used were: 1 percent, 3 percent, 5 percent, 7 percent and 28 percent (control). Weanling rats submitted to protein-free diet and adult rats submitted to that and other low-protein diets (1 percent, 3 percent or 5 percent casein) presented weight reductions (-0.38 +/- 0.07 g/day and -0.98 +/- 0.19 g/day, respectively). Only in young animals did these weight reductions parallel those of food consumption (37 +/- 12 percent of control), plasma protein (52 +/- 11 percent of control), plasma albumin (70 +/- 12 percent of control), hepatic RNA (68 +/- 7 percent of control) and protein (71 +/- 8 percent of control). A marked effect of the protein restriction, increasing the GGT activity, was also observed only in young rats. A significant (P<0.05) rise was promoted by the protein-free diet in the plasma GGT (2.83 +/- 1.39 vs 0.69 +/- 0.50 mU/ml for control) and by both the protein-free and 3 percent casein diets, in the liver GGT (respectively, 16.00 +/- 6.72 and 7.75 +/- 3.49 vs 0.94 +/- 0.57 U/g protein for control). The different results obtained for young in relation to mature animals could be explained by the reduction of both protein and sulfur-containing amino acid requirements with aging.

Rice and beans: effect of milk, mineral, and vitamina A, on weight gain, food intake, and body protein retention

Ratas recién destetadas fueron alimentadas con dietas de: arroz/frijoles (RB) suplementadas o no con minerales (M); vitamina A (A); M + A (MA), o leche (L), que contenían de 3 a 14% de proteína. Según se determinó a través de diversas mediciones, los mejores reutlados se observaron en el grupo alimentado con la dieta RB suplementada con L, seguido por los grupos que recibieron las dietas MA y M. La utilización proteínica de la dieta de RB, así como el requerimiento mínimo de proteína para mantenimiento de peso corporal, depende de los nutrientes suploementarios. Puede que el mecanismo de este efecto esté relacionado con el apetito de los animales y con la ingesta energética voluntaria, la que es influencia y regulada por la composición d ela dieta