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  • Title: Role of endothelium and nitric oxide in the in vitro response of equine colonic venous rings to vasoconstrictor agents.
    Author: Moore RM, Venugopalan CS, Sedrish SA, Holmes EP.
    Journal: Am J Vet Res; 1997 Oct; 58(10):1145-51. PubMed ID: 9328669.
    Abstract:
    OBJECTIVE: To determine in vitro contractile responses of equine colonic veins to various vasoconstrictor agents. ANIMALS: Colonic veins collected from 8 adult horses. PROCEDURE: Veins were cut into 4-mm-wide rings, placed in organ baths at 37 C, and attached to a force-transducer interfaced with a polygraph; 2 g of tension was applied, and rings were allowed to equilibrate for 45 minutes. Bath solution was replaced, and tension was reapplied at 15-minute intervals. Cumulative concentration responses (10(-8) to 10(-4) M) were determined for each agent, using separate rings (n = 8). Three vein groups were evaluated: endothelium-intact, endothelium-denuded, and N omega-nitro-L-arginine methyl ester (L-NAME, 10(-5) M)-treated. Maximal responses by each vein to each agent were considered 100%; responses to lower concentrations were calculated as percentage of maximum. RESULTS: Considering all vein groups, comparison of the doses that caused 50% of the maximal contraction revealed relative sensitivity of colonic veins to be: angiotensin II (ANG) > thromboxane B2 analogue (TXB) > 5-hydoxytryptamine (5HT) > norepinephrine (NE) > histamine (HST) > prostaglandin F2 alpha (PGF) > vasopressin (VP). Compared with ANG, PGF, TXB, and VP, treatment with HST, 5HT, and NE evoked significantly greater responses. Endothelium-denuded and L-NAME-treated colonic veins had significantly greater maximal contractile responses than did endothelium-intact veins. CONCLUSIONS: Response of colonic veins to vasoconstrictor agents was differential; sensitivity was not altered by endothelium removal or L-NAME treatment; maximal responses of endothelium-intact veins were greater than those of endothelium-denuded and L-NAME-treated veins; and responses of endothelium-denuded and L-NAME-treated veins were not different. CLINICAL RELEVANCE: Alterations in colonic veins that mimic conditions associated with large-colon volvulus may contribute to blood flow alterations, edema formation, and vascular responses to hypovolemic and endotoxic shock.
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