DIETARY MANGANESE DEFICIENCY DECREASES RAT HEPATIC ARGINASE ACTIVITY

This study was designed to quantify the effect of dietary manganese de ficiency on rat hepatic Mn concentration and arginase activity. Weanli ng male Sprague-Dawley rats were randomly assigned to two groups of ni ne rats each and fed L-amino acid diets with 0 or 48 mu g Mn/g diet fo r 21 d. After 21 d, hepatic Mn concentration (mu mol/g liver dry wt, m ean +/- SEM) was 0.130 +/- 0.005 for the control group but was lower ( P < 0.01) in the Mn-deficient group (0.040 +/- 0.003). There were no d ifferences in the hepatic concentrations of any other measured mineral . Hepatic arginase activity [mmol ornithine/(g hepatic protein min)l w as 1.55 +/- 0.22 in the control group and was lower (P < 0.01) in the Mn-deficient group (1.12 +/- 0.26). Plasma ammonia concentration was 3 01 +/- 6 mu mol/L in the control group and was higher (P < 0.01) in th e Mn-deficient group (480 +/- 8 mu mol/L). In contrast, plasma urea co ncentration was higher (P < 0.01) in the control group (350 +/- 10 mu mol/L) than in the Mn-deficient group (267 +/- 7 mu mol/L). There were no differences in plasma concentrations of arginine or other amino ac ids between the control and the Mn-deficient groups. Our results demon strate for the first time that dietary Mn deficiency results in altere d plasma concentrations of ammonia and urea in association with decrea sed hepatic Mn concentration and arginase activity in young growing ra ts.