ENDOTHELIAL DYSFUNCTION COINCIDES WITH AN ENHANCED NITRIC-OXIDE SYNTHASE EXPRESSION AND SUPEROXIDE ANION PRODUCTION

We investigated the effects of aortic banding-induced hypertension on the endothelium-dependent vasodilator responses in the aorta and coron ary circulation of Sprague-Dawley rats. We studied the influence of hy pertension on the endothelial nitric oxide synthase (NOS III) expressi on, assessed by Western blot and reverse transcription-polymerase chai n reactions experiments, and on the superoxide anion (O-2(-)) producti on. Two weeks after aortic banding, the endothelium-dependent relaxati ons were not altered. At this time, the expression of NOS III in the a orta and in confluent coronary microvascular endothelial cells (RCMECs ) exhibited no marked changes, whereas O-2(-) production was enhanced 1.9-fold in aortas from aortic-banded rats. Six weeks after aortic ban ding, the endothelium-dependent dilations were markedly impaired in th e heart (50% decrease) and aorta (35% decrease). Analysis of NOS III p rotein and mRNA levels revealed marked increases in both aortas and co nfluent RCMECs (2.6- to 4-fold) front aortic-banded compared with shar n-operated rats. There was no further increase in O-2(-) production in both the aorta and confluent RCMECs from aortic-banded rats. An enhan ced nitrotyrosine protein level was also detected in the aorta from 6- week aortic-banded rats. These findings indicate that in hypertension induced by aortic banding, an enhanced O-2(-) production alone is not sufficient to produce endothelial dysfunction. Endothelial vasodilator hyporesponsiveness was observed only when NOS III expression and O-2( -) production were increased and was associated with the appearance of enhanced nitrotyrosine residues. This would suggest that the developm ent of endothelial dysfunction is linked to an overproduction of not o ne, but two, endothelium-derived radicals that might lead to the forma tion of peroxynitrite.