Neuromuscular transmission in intramural blood vessels

Functional characterization of neuronal pre and postsynaptic α2‐adrenoceptor subtypes in guinea‐pig submucosal plexus

“…We have not examined this action of ARC-239 further. Prazosin (1-30 pM) did not alter the nerve evoked vasoconstriction (n = 9); prazosin has previously been shown to be ineffective in blocking excitatory junction potentials recorded from submucosal arterioles in response to sympathetic nerve stimulation (Hirst, 1989). Prazosin (10uM) also did not alter the inhibition of the nerve-evoked vasoconstriction by UK 14304 (n = 4).…”

“…c2-Adrenoceptor on sympathetic nerve terminals innervating submucosal arterioles Excitatory junction potentials (ej.ps) recorded from submucosal arterioles in response to sympathetic nerve stimulation are insensitive to blockade by high concentrations of prazosin (Hirst, 1989). These ej.ps have been attributed to the release of ATP from sympathetic nerves (Burnstock & Griffith, 1988) or to activation of a distinct noradrenaline receptor (Hirst, 1989). In the present study, the nerve-evoked vasoconstriction of submucosal arterioles was similarly insensitive to prazosin; 10-30,UM prazosin did not alter the amplitude or time course of the nerve evoked vasoconstriction.…”

“…In the present study, the nerve-evoked vasoconstriction of submucosal arterioles was similarly insensitive to prazosin; 10-30,UM prazosin did not alter the amplitude or time course of the nerve evoked vasoconstriction. On the other hand, submucosal arterioles readily constrict when noradrenaline or phenylephrine is applied (Hirst, 1989;Neild & Kotecha, 1989) and this vasoconstriction is antagonized by prazosin with a KD of 1 nM (Vanner et al, 1990). Thus, it appears that noradrenaline released from sympathetic nerves to submucosal arterioles by even high frequency stimulation does not activate the ax-adrenoceptors present on the vascular smooth muscle.…”

“…Noradrenaline hyperpolarizes submucosal neurones, inhibits the release of acetylcholine from (cholinergic) submucosal neurones as well as the release of sympathetically released neurotransmitter onto submucosal arterioles (North & Surprenant, 1985;Suprenant, 1989;Hirst, 1989). The postsynaptic adreno-I Author for correspondence.…”

Acetylcholine released from guinea‐pig submucosal neurones dilates arterioles by releasing nitric oxide from endothelium.

“…Stimulation of cholinergic neurones in the submucosal plexus of the guinea-pig intestine produces a muscarinic vasodilatation in adjacent arterioles; this has been shown directly by making intracellular recordings from single submucosal neurones and recording arteriolar vasodilatations in response to intracellular depolarization of the neurone (Neild, Shen & Surprenant, 1990). Submucosal arterioles are composed of a single layer of vascular smooth muscle cells overlying a single layer of endothelial cells and have a total vessel wall thickness of 4-10 1am (Hirst, 1989). These physical and physiological features provide a well-defined system in which to investigate the involvement of the endothelium in mediating neurogenic cholinergic vasodilatations in resistance vessels, and such was the primary aim of the present study.…”