Comparison of 2 endothelin-receptor antagonists on in vitro responses of equine palmar digital arterial and venous rings to endothelin-1

摘要

The goals of this study were to determine the concentration–response (C–R) relationship of endothelin-1 (ET-1), compare 2 ET-receptor antagonists and determine the antagonist concentrations that block the vasomotor effects of ET-1, and compare the effectiveness of ET-1 and previously studied vasoconstrictors in equine palmar digital arterial and venous rings in vitro. Vessel rings from 8 nonlaminitic horses were placed in Tyrode’s solution, 1 side fixed to the floor of an organ bath and the other side fixed to a force-displacement transducer. Two separate studies were conducted: (I) incubation with a single ET-receptor antagonist (PD142893 or PD145065 at a concentration of 10⁻⁷, 10⁻⁶, or 10⁻⁵ M), followed by determination of an ET-1 C–R curve (using concentrations of 10⁻¹⁰ to 10⁻⁶ M) for medial vessel rings; and (II) comparison of ET-1 with norepinephrine and histamine (10⁻¹⁰ to 10⁻⁶ M) and comparison of contractile responses of medial and lateral vessel rings. In study I, ET-1 administration caused pronounced and sustained concentration-dependent contraction of vessel rings; these contractile responses were decreased by 10⁻⁵ M PD142893 and were completely blocked by 10⁻⁵ M PD145065. Venous rings had greater apparent maximum contraction in response to ET-1 than arterial rings. In study II, the relative sensitivity of norepinephrine was found to be equivalent to that of ET-1, whereas that of histamine was lower. No significant differences were observed between responses of medial versus lateral vessel rings. Thus, ET-1 is a potent vasoconstrictor of equine palmar digital arteries and veins, and the ET-receptor antagonist PD145065 is more effective than PD142893 in inhibiting these contractile effects in vitro.