FURTHER STUDIES ON URINARY 3-METHYLHISTIDINE EXCRETION AS AN INDIRECT INDEX OF DIETARY AMINO ACID ADEQUACY IN RATS

Abstract

As a further step in the determination of the sen­sitivity of urinary 3-methylhistidine (3-MeH) to essential amino acid adequacy in diet, 36 male albino rats of the Wistar strain were divided into six groups +of six rats per group. Each group with an initial .mean live weight of 106.52 ± 0.54g was fed in in­dividual metabolic cages on a basal diet sup­plemented with graded levels of DL-methionine. Total methionine in diet ranged between 0.25 and 1.05%. The study lasted 10 days. The response of urinary 3-methylhistidine excretion to the graded levels of methionine in diet was compared to responses obtained from growth performance characteristics, plasma urea concentration, liver nitrogen and creatinine excretion. With the excep­tion of feed intake, all other indices of dietary pro­tein adequcy and efficient amino acid utilization viz growth rate, protein efficiency ratio, serum urea concentration, and creatinine excretion were significantly (P 0.05) to P 0.01) influenced by dietary methionine level. Maximum growth rate, liver N and urinary 3-methylhistidine were observed_. in rats given 0.45% total methionine in diet. Supplementing the basal diet to contain 0.45% total^,' methonine significantly (P 0.01) decreased serum urea concentration. Urinary 3-methylhistidlne excre­tion was found by regression analysis to be positively correlated to body weight gain (r = 0.73), feed intake (r = 0.61), urinary creatinine excretion (r = 0.74) and liver N (0.72) but negatively correlated to dietary methionine level (r = —0.41). We suggested that urinary 3-MeH excretion be added to the list of available indicts for dietary amino acid adequacy.