Levels of Histidine and Histidine Derivatives in Breast Muscle of Protein-depleted and Repleted Adult Cockerels

Four groups of adult cockerels, consisting of a control group given adequate protein, a protein-depleted group, and two groups that had been given, respectively, a low and a higher nitrogen-containing diet following protein depletion, were killed after appropriate time intervals and histidine and histidine derivatives analyzed in breast muscle extract. The concentration of l-methylhistidine increased more than 12-fold during protein depletion and returned to near control levels during repletion. Carnosine decreased during depletion to less than 1/20 of the concentration in controls, yet increased more rapidly during repletion in the group fed a low-nitrogen diet free of histidine compared to the group fed a high-nitrogen diet containing histidine. Depleted cocks showed an elevation in the concentration of free histidine which decreased toward control levels after repletion. Levels of 3-methylhistidine were highest in the cocks fed diets containing histidine. Evidence for an accumulation in the breast muscle of adult cocks of 3-methylhistidine consisted of unusually high ratios of this derivative to muscle protein in all experimental groups. It was suggested that both 3-methylhistidine and 1-methylhistidine might serve as useful indices for assessing protein depletion in the adult cockerel, but that consideration should be given to the possibility of species differences in the metabolism of histidine derivatives during protein depletion.