Phenylephrine induces relaxation of longitudinal strips from small arteries of goat legs.

Kawin Padmaja Marconi,Bhavithra Bharathi,Alen Major Venis,Sathya Subramani,Soosai Manickam Amirtham,Renu Raj,Michael Bader

doi:10.1371/journal.pone.0227316

Abstract

Alpha adrenergic stimulation is known to produce vasoconstriction. We have earlier shown that, in spiral strips of small arteries Phenylephrine (PE) caused vasorelaxation under high nitric oxide (NO) environment. However, on further experimentation it was realized that the PE-induced vasorelaxant response occurred only with longitudinal strips of small arteries even under normal NO environment while circular strips showed contraction with PE even under high NO environment. Such PE-induced vasorelaxation of longitudinal strips was blocked by Phentolamine, an alpha-adrenergic receptor blocker. On delineation of specific receptor subtype, PE-induced relaxation was found to be mediated through alpha 1D receptor. However, this phenomenon is specific to small artery, as longitudinal smooth muscle of aorta showed only contractile response to adrenergic stimulation. There is no prior report of longitudinal smooth muscle in small artery up to our knowledge. The results of this study and histological examination of vessel sections suggest the presence of longitudinal smooth muscle in small artery and their relaxant response to alpha adrenergic stimulation is a novel phenomenon.

Highlights

Phenylephrine (PE) is an alpha-adrenergic agonist which is known to cause contraction of vascular smooth muscle
The results of this study suggest the presence of longitudinal smooth muscle in small arteries, and their relaxant response to alpha adrenergic stimulation is a novel phenomenon
The concentration of PE for the experiments on aortic as well as small artery preparations was chosen as 100μmol/L because the small artery preparation did not show a response to 10μmol/L PE

Summary

Introduction

Phenylephrine (PE) is an alpha-adrenergic agonist which is known to cause contraction of vascular smooth muscle. We had recently reported that Phenylephrine caused relaxation of spiral strips made from small arteries from goat legs in a high nitric oxide environment, while causing contraction in normal circumstances. With further experimentation we have realized that longitudinal strips made from small arteries always relaxed with Phenylephrine, even in normal nitric oxide environment. PE caused contraction of circular strips of small arteries even in a high nitric oxide environment.

Methods

Results

Conclusion