The inhibitory effects of the endothelium against ergonovine-induced contraction were examined in isolated porcine coronary arteries under normal conditions and after endothelial regeneration. Endothelium-dependent responses were examined in vitro in normal Yorkshire pigs (n = 16) and in pigs that had undergone balloon endothelium removal of the left anterior descending coronary artery (LAD) 4 weeks before the study (n = 10). The presence of a complete endothelial lining was confirmed histologically. In rings from normal arteries contracted with prostaglandin F(2α) in the presence of indomethacin and ketanserin (a 5-HT2-serotonergic blocker), ergonovine caused endothelium-dependent relaxations. They were attenuated by rauwolscine (an α2-adrenergic blocker), inhibited by methiothepin (a combined 5-HT1- and 5-HT2-serotonergic blocker) or by pertussis toxin (an inhibitor of several G proteins) and abolished by oxyhemoglobin (a selective inactivator of endothelium-derived relaxing factor). In quiescent rings from normal arteries, ergonovine caused contractions that were inhibited by the presence of the endothelium; this endothelium-dependent inhibition was ablished by oxyhemoglobin. The direct contractions were not affected by prazosin (an α1-adrenergic blocker), rauwolscine, 6-hydroxydopamine (an agent causing chemical sympathectomy), or diphenhydramine (an H1-histaminergic blocker) but were inhibited by ketanserin. In rings with regenerated endothelium contracted with prostaglandin F(2α), the endothelium-dependent relaxations to ergonovine were reduced significantly and were not inhibited by pertussis toxin. In quiescent rings with regenerated endothelium, the endothelium-dependent inhibition of ergonovine-induced contraction was less. Oxyhemoglobin caused endothelium-dependent contractions in quiescent rings (an indirect index of basally released endothelium-derived relaxing factor) that were reduced significantly in quiescent rings with regenerated endothelium. These results indicate that 1) the endothelium exerts its inhibitory action against ergonovine-induced contractioins by the release of endothelium-derived relaxing factor under basal conditions and upon stimulation by ergonovine, 2) endothelium-dependent relaxations to ergonovine are mediated mainly by 5-HT1-serotonergic receptors, whereas the direct contractions are mediated by 5-HT2-serotonergic receptors with little contribution of α-adrenoceptors, 3) the inhibitory role of the endothelium is impaired significantly in the regenerated state because of the reduced ability to release the relaxing factor, and 4) endothelial pertussis toxin-sensitive G protein may be involved in the synthesis of the relaxing factor upon stimulation by ergonovine, and dysfunction of the G protein may account partly for the dysfunction of regenerated endothelium.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)