Efficacy of ornithine-alpha-ketoglutarate (OKGA) as a dietary supplement in growing rats

Abstract

New substrates of potential benefit to critically ill patients receiving traditional nutritional support have been suggested to meet organ or tissue specific needs. The addition of an anabolic stimulus during nutritional support therefore appears to be a reasonable adjunct to augment protein synthesis. The purpose of this investigation was to evaluate the efficacy of the neutral salt ornithine alphaketoglutarate (OKGA) as a dietary supplement to promote growth in young rats by enhancing protein metabolism. A group of 16 male Sprague-Dawley rats (150–170g) were housed in individual metabolic cages and after dark-light cycle adaptation were fed ad libitum an oral liquid diet for 7 days. Half of the animals were given the control diet and the other half was fed a test diet. This isonitrogenous test diet contained the control diet with 2.3% of nitrogen (N) replaced by N from OKGA. Daily weight, food intake and urinary excretions of N, creatinine, urea, orotic acid, polyamines and amino-acids were determined. At the end of 7 days of free-feeding, the rats were sacrificed and blood was collected for free amino-acids. Rats fed the OKGA supplemented diet consumed 16% more diet, retained 11% more nitrogen and gained 15% more weight. The accelerated protein metabolism is reflected in the changes in plasma and urinary free amino-acid levels. Enhanced protein anabolism is evident from the increased urinary excretion of polyamines in the OKGA fed rats. The increased ratio of urinary urea N to total N and the decreased orotic acid excretion in OKGA fed rats suggests thata NH 4 + was efficiently diverted through urea cycle. It is concluded that in growing rats, supplementing isonitrogenous diet with OKGA significantly stimulates food intake compared to controls. This results in better weight gain and improvement in protein metabolism.