BACKGROUND: Glutamine is known to have a specific role in very old rats (>25 months of age). For this reason, we have orally supplemented female rats with glutamine (20% of diet protein) intermittently. The treatment started before animals became very old and lasted 5 months. Very old rats were studied in fed state or after 5-day fasting after the last glutamine cure. The aim of this study was to determine whether this in vivo pretreatment improves the well-being of very old rats (muscle sarcopenia decrease, gut integrity improvement, decrease of the known up-regulated glutamine synthetase observed regardless of nutrition state). METHODS: Protein turnover was measured in epitrochlearis muscle, whereas glutamine synthetase (GS) activities were assessed in tibialis anterior muscle from fed and 5-days-fasted female Wistar adult (6 months) and very old (27 months) rats, pretreated or not with glutamine. Furthermore, gut was dissected and weighed. RESULTS: Long-term treatment with glutamine had positive effects on very old rats: (1) it prevented the loss of body weight, but, (2) it did not prevent the inevitable sarcopenia regardless of nutrition state, and (3) it maintained the gut mass. Surprisingly, the muscle up-regulated GS activity observed in fed and fasted very old rats was only decreased in the fed state when rats were supplemented, without change in plasma and muscle glutamine concentrations. CONCLUSIONS: Long-term treatment with glutamine started before advanced age had essentially a beneficial role on the gut. It may play a role in maintaining intestine integrity and intestinal immune function. Further investigations would be warranted to explore these mechanisms.