Pharmacology of the new selective A2a adenosine receptor agonist 2-hexynyl-5'-N-ethylcarboxamidoadenosine

The pharmacological profile of 2-hexynyl-5'-N-ethylcarboxamidoadenosine (2HE-NECA, CAS 141018-30-6), a new selective A2a adenosine receptor agonist, was characterized. In binding studies on both rat and bovine brain, 2HE-NECA was more potent on A2a receptors (Ki = 2.2 and 1.5 nmol/l, respectively) than the reference A2a agonist, 2-[4-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoaden osi ne (CPEC) or the non-selective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA). The drug displayed a good A2a vs A1 receptor selectivity in brain tissues of both animal species (60- and 160-fold, respectively). In functional studies, 2HE-NECA showed marked vasodilating properties in rat aorta, bovine and porcine coronary arteries. The vasodilatory response in the porcine coronary preparation was greater for 2HE-NECA (EC50 = 23.3 nmol/l) than for CPEC (EC50 = 58.7 nmol/l) or NECA (EC50 = 76.6 nmol/l). In the rat Langendorff model, in which global ischemia was induced, 2HE-NECA (100 nmol/l) significantly prevented the risk of diastolic pressure and coronary perfusion pressure occurring during postischemic reperfusion. The in vitro antiaggregatory activity of 2HE-NECA (IC50 = 0.07 mumol/l), as tested in rabbit platelets, was higher than that found with NECA (IC50 = 0.2 mumol/l) or CPEC (IC50 = 2.16 mumol/l). In spontaneously beating rat atria, which are responsive to A1-receptor stimulation, 2HE-NECA did not show any negative chronotropic activity up to micromolar concentrations. In conscious spontaneously hypertensive rats, 2HE-NECA administered intraperitoneally caused a dose-dependent reduction in systolic blood pressure (ED30 = 0.005 mg/kg) with minimal reflex tachycardia.