title: Endothelin-1 is not involved in hemoglobin associated vasoactivities.
abstract: This study tested the hypothesis: is hemoglobin (Hb) associated vasoconstriction mediated by endothelins (ET)? Two millimeter segments of the thoracic aorta with intact endothelium were obtained from Sprague-Dawley rats (200-350g) and suspended in oxygenated Krebs buffer (37C, pH 7.4). The vessels were equilibrated at 2g of imposed tension for 1 hour. After submaximal tone was induced with norepinephrine (50nM), the presence of functional endothelium was verified by an acetylcholine (33uM) dilation test. The vessel rings were then treated with either ET-1 (3nM) or human stroma-free Hb (SFH; 2.2uM) and vascular response characteristics observed. Subsequently, the vessel rings were treated with BQ-123 (15uM), an ET-1 receptor antagonist, to test whether the ET-1 pathway is involved in the Hb associated vasoconstriction. Both ET-1 and SFH elicited contractory responses in aortic rings; the maximal tension increases at the doses tested were 54.8 +/- 8.5% and 39.2 +/- 22.5%, respectively, over the pretreatment values. The contractory response characteristics were, however, distinct; ET-1 caused a slow (time to maximal response; TMR = 28.8 +/- 6.4 min, N = 6) but prolonged contraction (> 30 min) while SFH caused a faster contraction (TMR = 7.2 +/- 1.7 min, N = 6) with a shorter duration (< 30 min). The TMR of ET-1 treated rings were significantly longer than that of SFH (P < 0.0005, t-test). Treatment with BQ-123 caused an immediate reversal of the SFH induced contraction but had no significant effect on the SFH induced contraction. If the Hb associated vasoconstriction were mediated by ET-1, BQ-123 should have also reversed the contraction. These results suggest that ET-1 pathway is not involved in the Hb mediated vasoconstriction.
authors.affiliation: Department of surgery, Miriam Hospital, Providence, Rhode Island, USA.
authors.forename: J
authors.initials: J
authors.lastname: Tai
authors.forename: H W
authors.initials: HW
authors.lastname: Kim
authors.forename: A G
authors.initials: AG
authors.lastname: Greenburg
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000096:biosynthesis / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D006454:Hemoglobins / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010456:Peptides, Cyclic / Q000494:pharmacology; D010952:Plasma Substitutes / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D006454:Hemoglobins; D010456:Peptides, Cyclic; D010952:Plasma Substitutes; C016484:hemoglobin, stroma free; C072247:cyclo(Trp-Asp-Pro-Val-Leu)