l-Glycyl-l-glutamine provides the isolated and perfused young and middle-aged rat heart protection against ischaemia–reperfusion injury

The amino acids glycine and glutamine have been implicated in myocardial protection of the much studied young adult heart. This study aimed to determine whether such protection could be enhanced using the dipeptide, l-glycyl-l-glutamine (gly-gln) in both young hearts and in middle-aged hearts representative of a more clinically relevant age group. Hearts from 8-week-old and 36-week-old rats were perfused in the Langendorff mode for 20 min, before 40 min global normothermic ischaemia and 30 min reperfusion. Where present, 0.5, 2, or 5 mM gly-gln was added 10 min into baseline perfusion, was present throughout ischaemia and was washed out after 10 min reperfusion. Reperfusion damage was assessed from the release of lactate dehydrogenase. Metabolic fitness was assessed from the time to ischaemic contracture and the accumulation of lactate and thiobarbituric acid reactive substances during ischaemia. The presence of 5 mM gly-gln significantly improved the post-ischaemic rate pressure product (RPP) and decreased reperfusion damage in both the 8 (RPP in control on reperfusion 5527 ± 957  vs. 10,320 ± 795 mmHg beat min−1 in 5 mM gly-gln, n = 6 ± SE, p < 0.05) and 36-week-old (RPP in control on reperfusion 1964.33 ± 876.3 vs. 4008 ± 675 mmHg beat min−1, n = 6 ± SE, p < 0.01) hearts. Five mM gly-gln also increased the time to ischaemic contracture and was able to protect against the rise in lactate that occurred in the controls during ischaemia. These results suggest that gly-gln has good potential as a combatant against ischaemia–reperfusion injury in both the young adult and middle-aged populations.