Blockade of arginase activation, addition of L-arginine, and scavenging of superoxide improve serotonin-induced dilation of coronary arterioles isolated from diabetic pigs. (A) The serotonin-induced dilation was compared between euglycemic control (n = 13) and diabetic (n = 13) vessels. In another cohort of diabetic vessels, vasodilation to serotonin was examined in the presence of arginase inhibitor nor-NOHA before (n = 10) and after (n = 6) treatment with L-NAME, or after administration of L-arginine (n = 3). (B) The serotonin-induced dilation was compared between euglycemic control (n = 19) and diabetic (n = 20) vessels. In another cohort of diabetic vessels, vasodilation to serotonin was examined in the presence of superoxide dismutase mimetic TEMPOL alone (n = 9) or combined with arginase inhibitor nor-NOHA (n = 7), or after administration of hydrogen peroxide scavenger catalase (n = 5). *P<0.05 vs. Control, #P<0.05 vs. Diabetes, two-way ANOVA with Bonferroni multiple-range test.