VASODILATION IN PORCINE OPHTHALMIC ARTERY - PEPTIDE INTERACTION WITH ACETYLCHOLINE AND ENDOTHELIAL DEPENDENCE

Co-activation of cranial perivascular sensory and parasympathetic fibr es in vivo induces simultaneous release of several vasodilatory substa nces with neurotransmitter or neuromodulatory roles. The role of the e ndothelium and possible interactions between such substances are poorl y understood. The objective of this study was therefore to investigate these aspects with the sensory dilator calcitonin gene-related peptid e (CGRP) and the parasympathetic dilators acetylcholine (ACh) and vaso active intestinal peptide (VIP) in isolated porcine ophthalmic artery. Whilst ACh induced relatively rapid, endothelium-dependent dilation, CGRP and VIP induced slower dilations. Both CGRP and VIP were found to have partial endothelium-dependence in this artery. The simultaneous addition of ACh with CGRP potentiated the relaxation induced by CGRP, as has already been shown for substance P. ACh did not potentiate VIP relaxation, but the results generally indicate a potential role for AC h in initiating rapid dilation prior to strong, sustained relaxation b y CGRP or VIP. The potential role of the endothelium and of substances like ACh or substance P in enhancing the rate of dilation of neuropep tides inducing strong and sustained relaxation is discussed.