Extrinsic and intrinsic cholinergic systems of the vascular wall

Immunohistochemical, biochemical and functional studies have revealed two s eparate cholinergic systems in the arterial vascular wall. Endothelial cell s represent the ubiquitous intrinsic, intimal system; they contain the acet ylcholine-synthesizing enzyme, choline acetyltransferase, release a choline eater, and contain functional muscarinic receptors. Perivascular autonomic nerve fibres represent the extrinsic, adventitial system. These axons are not ubiquitous but show a highly selective distribution among and even with in organs, and utilize co-mediators (NO, neuropeptides) in an organ-specifi c pattern. We put forward the hypothesis that the intrinsic, intimal system serves as a general regulator of basal vascular tone and wall structure re sponding to local, luminal stimuli, whereas the perivascular nerve fibres a ct on top of this basal tone by providing fine tuning in response to reflex activation due to systemic demands.