MAPK1 and myocardial ischemia: Finally, it is worth mentioning that enhancing O-GlcNAcylation by glucosamine perfusion blunts the phosphorylation of p38 during cardiac ischemia but increases it during reperfusion, further underscoring a tight but complex relationship between O-GlcNAcylation and p38 phosphorylation in the intact heart (11).