Modulation of sympathetic nerve activity by perivascular sensory nerves inthe arterioles of the guinea-pig small intestine

Objective: The aim of this study was to assess the role of perivascular sen sory nerves in modulating constrictions of intestinal submucosal arterioles . Methods: Arteriole constrictions were induced either by nerve released ad enosine 5'-triphosphate (ATP) or exogenous ATP or phenylephrine (PE). Indiv idual nerve shocks were used to elicit excitatory junction potentials (EJPs ) in the arteriole smooth muscle whereas trains of stimuli were used to evo ke transient constrictions of the arteriole. Effects of the sensory neuroto xin, capsaicin, were examined on constrictions and EJPs. Results: Pre-treat ment of the arteriole preparation with capsaicin did not cause any signific ant change in the amplitude of arteriole constrictions to exogenously appli ed ATP or PE. However, there was a significant increase in the amplitude of neurally evoked arteriole constrictions and EJPs, without a significant ch ange in the decay time constant (tau(decay)) of the EJPs. Exogenous applica tion of calcitonin gene related peptide (CGRP) significantly decreased tau( decay) of the EJPs without affecting their amplitude, whereas substance P ( SP) significantly decreased the amplitude of EJPs without affecting tau(dec ay). Both, CGRP and SP, decreased the amplitude of neurally evoked and ATP induced constrictions. Whilst the inhibitory effects of CGRP on evoked and ATP induced constrictions were not significantly different, the reduction i n evoked constrictions obtained with SP was significantly greater than the reduction in ATP induced constrictions. SP antagonist significantly increas ed the amplitude of neurally evoked constrictions. Conclusions: It is concl uded that capsaicin-sensitive afferents inhibit the release of transmitter from perivascular sympathetic nerves via the prejunctional modulatory actio n of SP. The other putative sensory neurotransmitter, CGRP, appears to act postjunctionally on the arteriole smooth muscle. (C) 1999 Elsevier Science B.V. All rights reserved.