[Immunohistochemical study of the distribution of constitutive nitric oxide synthase in vascular endothelium of the nasal mucosa in the human].

Human nasal mucosa is a highly regulated tissue that performs a wide range of physiological functions. In addition to the classic and peptidergic neurotransmitters, the endogenously produced free radical gas nitric oxide (NO) has been found to be increasingly important for the vascular regulation of this tissue. NO-dependent control of vascular tone works in two ways, consisting of neurally produced NO acting as a neurotransmitter on the one hand and endothelially produced NO on the other hand. Neurons and endothelial cells contain various isoforms of the enzyme nitric oxide synthase, which forms NO out of L-arginine. The aim of this study was to examine the distribution of endothelial constitutive NO-synthase (ecNOS) in the human nasal mucosa of inferior turbinates. Immunocytochemistry (avidin-biotin method) with polyclonal and monoclonal antibodies against eNOS and cluster of differentiation 31, a marker for endothelial and certain blood cells, was used in order to gain more detailed information on the physiological distribution and significance of NOS in vascular endothelium of different vessel types. Positive eNOS-immunoreactions were found in the endothelial cells of arterial blood vessels of different diameters as well as in capillaries and postcapillary venules. Venous sinuses with or without subendothelial cushions did not show any immunoreactions. There is strong evidence that vascular tone in human nasal mucosa is not only subject to nerval control, but also influenced directly by mediators released from the endothelium. The present results lead to the conclusion that in physiological conditions endothelially produced NO has an influence on the arterial component of the swelling mechanism in human nasal mucosa. Because eNOS could also be detected in capillaries and postcapillary venules, NO might also play an important role in plasma extravasation.