Effect of an enterally administered glutamine-rich protein on the catabolic response to a zymosan challenge in rats

Glutamine is considered to be a conditionally essential amino acid during critical illness and has, therefore, been advocated to be included in nutritional support supplied in these situations. We investigated whether a diet containing a protein source rich in glutamine can restore depleted glutamine pools (plasma and muscle) and counteract muscle wasting, in a rat model of critical illness (intraperitoneal injection of zymosan). A glutamine-rich protein source was obtained by mixing a wheat protein hydrolysate (25% glutamine) with a whey protein isolate (to prevent essential amino acid deficiency). Feeding healthy control rats for 2 weeks with an adequate diet containing this protein source increased the two main glutamine pools (plasma and muscle). However, no effect was observed on the following zymosan-induced changes: 1) decreased glutamine and arginine concentrations (plasma and muscle), 2) wasting of muscle protein, and 3) decreased mitochondrial content in skeletal muscle. We conclude that a diet containing a glutamine-rich protein source can be used to increase plasma and muscle glutamine concentrations in healthy rats, but is of limited value to counteract wasting of skeletal muscle in zymosan-treated rats.