Diabetes is associated with cardiac inflammation and impaired endothelium-dependent coronary vasodilation, but molecular mechanisms involved in this dysfunction remain unclear. We examined contributions of inflammatory molecules lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), stress-activated kinases (c-Jun N-terminal kinase [JNK] and p38), arginase, and reactive oxygen species to coronary arteriolar dysfunction in a porcine model of type 1 diabetes. Coronary arterioles were isolated from streptozocin-induced diabetic pigs and control pigs for vasoreactivity and molecular/biochemical studies. Endothelium-dependent nitric oxide (NO)-mediated vasodilation to serotonin was diminished after 2 weeks of diabetes, without altering endothelium-independent vasodilation to sodium nitroprusside. Superoxide scavenger TEMPOL, NO precursor L-arginine, arginase inhibitor nor-NOHA, anti-LOX-1 antibody or JNK inhibitors SP600125 and BI-78D3 improved dilation of diabetic vessels to serotonin. However, hydrogen peroxide scavenger catalase, anti-IgG antibody or p38 kinase inhibitor SB203580 had no effect. Combined inhibition of arginase and superoxide levels did not further improve vasodilation. Arginase-I mRNA expression, LOX-1 and JNK protein expression, and superoxide levels were elevated in diabetic arterioles. In conclusion, sequential activation of LOX-1, JNK, and L-arginine consuming enzyme arginase-I in diabetes elicits superoxide-dependent oxidative stress and impairs endothelial NO-mediated dilation in coronary arterioles. Therapeutic targeting of these adverse vascular molecules may improve coronary arteriolar function during diabetes.