1. Archive
2. Vol.52, No.5

Plasma-Mediated Potentiation in Prostanoid-Induced Contractions in Isolated Canine External Jugular Veins

Abstract: We examined the effects of plasma on contractile responses of isolated dog external jugular veins to a thromboxane A₂ analog, U46619, and noradrenaline. Pretreatment with 1.0% plasma in Krebs-bicarbonate solution, but not 0.1%, caused a significant left and upward shift in the concentration–contractile response curve for U46619. The plasma-mediated potentiation of the response to U46619 was found in the venous segments without intact endothelium. The administration of 2×10⁻⁵ M lysophosphatidylcholine in Krebs-bicarbonate solution with no plasma also produced a significant left and upward shift of the concentration–contractile response curve for U46619, the shift being quite similar to that obtained with 1.0% plasma. In contrast, pretreatment with 1.0% plasma or 2×10⁻⁵ M lysophosphatidylcholine produced no significant effect on the noradrenaline-mediated contractions in the venous segments. Pretreatment with 10⁻⁴ M L-ascorbate or 0.1 mg/ml α-tocopherol in the presence of 1.0% plasma caused a significant reduction in the plasma-mediated potentiation of the contractile responses to U46619. These findings suggest that lysophosphatidylcholine, a major phospholipid component of oxidized low-density lipoproteins, may contribute, in part, to the plasma-mediated potentiation of contractile responses of the isolated veins to U46619, and that the antioxidant vitamin, L-ascorbate, or α-tocopherol significantly reduces the plasma-mediated potentiation of the contractile responses to U46619, which may be related to inhibiting the production of lysophosphatidylcholine in plasma.

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