NEUROPEPTIDES INDUCE RELEASE OF NITRIC-OXIDE FROM HUMAN DERMAL MICROVASCULAR ENDOTHELIAL-CELLS

Nitric oxide is a potent mediator of endothelium-dependent vasodilatat ion, the synthesis of which is catalyzed by the constitutively express ed enzyme endothelial nitric oxide synthase, In this study we have inv estigated whether human dermal microvascular endothelial cells express endothelial nitric oxide synthase and whether the vasodilator neurope ptides, calcitonin gene-related peptide and substance P, stimulate the release of nitric oxide from these cells, Endothelial nitric bride sy nthase was identified by immunohistochemistry in the blood vessels in both the papillary and deep dermis of normal skin, and also in monolay ers of human dermal microvascular endothelial cells, On western blots of protein extracts prepared from both the dermis of normal human skin and human dermal microvascular endothelial cells, a 135-kDa band corr esponding to endothelial nitric oxide synthase was identified. Nitric oxide was released from unstimulated human dermal microvascular endoth elial cells as assessed by inhibition of platelet aggregation and nitr ite formation. Endothelial cell-mediated inhibition of platelet agi gr egation was blocked by hemoglobin, which binds nitric oxide, Substance P (10 nM) potentiated microvascular endothelial cell inhibition of pl atelet aggregation, and this effect was also blocked by hemoglobin, Ca lcitonin gene-related peptide (100 pM to 100 nM) directly inhibited pl atelet aggregation, and this direct effect was not modulated by microv ascular endothelial cells, Substance P (10 nM to 1 mu M) and calcitoni n gene-related peptide (100 pM to 10 nM) significantly (p < 0.05) incr eased nitrite formation, and this increase was blocked by the competit ive nitric oxide synthase antagonist, N-G-monomethyl-L-arginine. These results demonstrate that endothelial nitric oxide synthase is express ed in the microvascular endothelium of normal human skin and that huma n dermal microvascular endothelial cells release nitric oxide constitu tively and in response to vasodilator neuropeptides.