Biological evaluation of the nitric oxide-trapping agent, N-methyl-D-glucamine dithiocarbamate-Fe2+, as a probe of nitric oxide activity released from control and diabetic rat endothelium

We utilized the nitric oxide (NO) scavenger N-methyl-D-glucamines dithiocar bamate-Fe2+ (MGD-Fe) to characterize the role of NO in basal and acetylchol ine (ACh)-stimulated relaxation arising from the endothelium of control vs diabetic rat aortic rings. In phenylephrine-contracted rings, MGD-Fe produc ed an additional increment in tension that was indomethacin-insensitive (i. e., excluding a role of prostanoids in this action), This MGD-Fe-sensitive component was more pronounced in control rings than diabetic rings and of t he same magnitude achieved in rings without MGD-Fe treatment: after removal of endothelium or treatment with the NO synthase inhibitor L-nitroarginine (L-NA). This suggests complete scavenging of basal Na by MGD-Fe and suppor ts reduced basal NO in diabetic rings. ACh fully relaxed both control and d iabetic rings. This relaxation was abolished by removal of the endothelium and was inhibited by L-NA (by 100% and 90% in control and diabetic rings, r espectively). In contrast, MGD-Fe only partially inhibited ACh-induced rela xation in control (65 +/- 5% inhibition) and diabetic (41 +/ -11% inhibitio n) rings. The MGD-Fe-resistant component was hot further modified by indome thacin. Addition of L-arginine (L-ARG) (but not D-arginine (D-ARG) enhanced the ACh-induced relaxation of MGD-Fe-treated diabetic (but not control) ri ngs. These data provide evidence about endothelium-dependent relaxation in control and diabetic rings which cannot be discerned by use of L-NA alone. This study suggests that ACh produces a NO synthase-dependent vasodilation, a portion of which is due to free NO radical (.NO) or due to NO in a form or location that is unavailable for scavenging by MGD-Fe.