Modulation of ACh Vasorelaxation by VIP in Ischemic Submandibular Artery

Objectives:It is known that in in vitro conditions VIP potentiates vasodilatory effect of ACh in submandibular gland and that in in vitro conditions ACh produces endothelium-dependent while VIP endothelium-independent vasorelaxation of rabbit submandibular branch of facial artery (feeding artery for submandibular gland). On the other hand, it is well established that ischemic conditions impair endothelium-dependent relaxation.Our aims were to examine, in vitro, modulatory effect of VIP on ACh-induced vasorelaxation under a)normal and b) in acute ischemic conditions, on isolated rabbit submandibular artery. Method:In organ bath studies with rings of rabbit submandibular artery changes in isometric tension were recorded on contralateral and ipsylateral side of common carotid artery occlusion after 10, 30 and 60 minutes. Relaxation was studied in vascular segments precontracted with phenylephrine (10 µM). Results:In control rings VIP(100 nM)potentiates vasorelaxant effect of ACh (1,3 and 10 µM). Maximal response of ACh-induced vasorelaxation in abscence of VIP was 97.0 ± 4.0% and in the presence 135.0 ± 4.5%. In ischemic conditions, the observed potentiating effect of VIP was smaller or absent.Maximal responses of ACh-induced vasorelaxation in the absence and presence of VIP after 10 minutes of occlusion were 95.0 ± 2.0% vs.115.6 ± 4.5%respectively, after 30 minutes of occlusion 70.0 ± 5.1% vs. 90.0 ± 4.3% respectively while after 60 minutes of occlusion there was no potentiation (54.0 ± 5.0% vs. 62.0 ± 4.5%). Conclusions: The results suggest that acute ischemic conditions in time-dependent manner decreases potentiation of ACh-induced vasorelaxation of rabbit submandibular artery by VIP.