Influence of dietary potassium on lysine metabolism in the chick

High levels of dietary cations have been reported to spare the arginine requirement of chicks fed a diet containing excess lysine. The present studies were conducted to determine the nature of this effect, using potassium as the variable cation. The inclusion of 1.8% potassium in a high lysine diet improved growth but did not affect consistently the efficiency of feed utilization, nor did it have a significant effect on arginine metabolism as measured by renal arginase activity, urea excretion or arginine excretion. Lysine catabolism was markedly increased, however. Chicks fed the potassium supplemented diet converted approximately 23% of an oral loading dose of 14C lysine to respiratory 14CO2 over a 6-hour period, in contrast to approximately 9% of the dose in chicks fed the unsupplemented diet containing 0.4% potassium. The activity of hepatic lysine-alpha-ketoglutarate reductase, an initial enzyme in the catabolism of lysine, was increased in response to potassium or arginine supplementation. It is proposed that high levels of potassium or other cations may improve the growth of chicks fed diets containing excess lysine by increasing lysine catabolism. The effect on growth may be mediated primarily by increasing food intake and to a lesser extent by alleviation of the other metabolic manifestation of the lysine-arginine antagonism.