In vivo assessment of microvascular nitric oxide production and its relation with blood flow

Unidad de Regulación Neurohumoral, Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile 6513492 To assess the hypothesis that microvascular nitric oxide (NO) is critical to maintain blood flow and solute exchange, we quantified NO production in the hamster cheek pouch in vivo, correlating it with vascular dynamics. Hamsters (100-120 g) were anesthetized and prepared for measurement of microvessel diameters by intravital microscopy, of plasma flow by isotopic sodium clearance, and of NO production by chemiluminescence. Analysis of endothelial NO synthase (eNOS) location by immunocytochemistry and subcellular fractionation revealed that eNOS was present in arterioles and venules and was 67 ± 7% membrane bound. Basal NO release was 60.1 ± 5.1 pM/min ( n = 35), and plasma flow was 2.95 ± 0.27 µl/min ( n = 29). Local NO synthase inhibition with 30 µM N -nitro- L -arginine reduced NO production to 8.6 ± 2.6 pmol/min ( 83 ± 5%, n = 9) and plasma flow to 1.95 ± 0.15 µl/min ( 28 ± 12%, n = 17) within 30-45 min, in parallel with constriction of arterioles (9-14%) and venules (19-25%). The effects of N -nitro- L -arginine (10-30 µM) were proportional to basal microvascular conductance ( r = 0.7, P