Ornithine-alpha-ketoglutarate (OKG) supplementation is more effective than its component salts in traumatized rats

Addition of an anabolic stimulus during nutritional support seems to be a reasonable adjunct to augment protein synthesis. Ornithine-alpha-ketoglutarate (OKG) has been used for this purpose in many pathological situations, but the mechanism of action is poorly understood. We have evaluated the relative metabolic efficacy of four isonitrogenous diets with or without the addition of alpha-ketoglutarate (alpha KG) or ornithine (ORN), in a rat trauma (bilateral femur fracture) model. Both control and traumatized rats were starved for 2 d. Then for 4 d, the control rats were pair-fed to the traumatized rats, one of the four isonitrogenous diets: the basal diet was a casein-based liquid diet; the ORN and OKG diets were the basal diet in which 10% of the dietary nitrogen was replaced by ORN- or OKG-nitrogen, respectively; the alpha KG diet contained equivalent amounts of alpha KG as were present in the OKG diet. Body weight gain per gram of nitrogen intake was similar in all four diet groups of both control and traumatized rats. The fraction of nitrogen intake that was retained in the body was significantly higher in OKG-fed traumatized rats (23%) than in the corresponding basal diet-fed rats. Plasma and muscle free amino acid concentrations were comparable in OKG- and ORN-fed rats but not in OKG- and alpha KG-fed rats. Our data suggest that the mechanism of OKG action may be associated with increases in growth hormone and insulin, as well as the production of metabolites of ORN and alpha KG. OKG has better metabolic benefits than its two components given separately in the nutritional support of injured rats.