Pharmacological probes for A1 and A2 adenosine receptors in vivo in feline pulmonary vascular bed.

Under conditions of controlled pulmonary blood flow and constant left atrial pressure, adenosine produces dose-dependent, tone-dependent responses in the pulmonary vascular (PV) bed of intact-chest, spontaneously breathing cats. The potency profile for adenosine receptor agonists to produce vasoconstriction at low baseline PV tone is 5'-(N-ethylcarboxamido)adenosine > or = CGS-21680 > or = 2-chloroadenosine (2-CADO) > or = [R]-N6-(2-phenylisopropyl)adenosine (R-PIA) > or = N6-cyclopentyladenosine > adenosine > > CV-1808. After an increase in PV tone with the use of an intralobar infusion of the thromboxane mimic U-46619, the potency profile for adenosine receptor agonists to produce vasodilation at elevated PV tone is 2-CADO > or = CV-1808 > or = CGS-21680 > R-PIA > or = adenosine. The selective A1 adenosine receptor antagonists xanthine amine congener (XAC) and 8-cyclopentyl-1,3-dipropylxanthine (DP-CPX) significantly antagonize the vasoconstrictor responses of adenosine and R-PIA at low baseline PV tone while having less effect on the vasodilator responses of adenosine, 2-CADO, and R-PIA at elevated PV tone. DPCPX antagonizes the vasoconstrictor responses of CGS-21680 at low baseline PV tone. The nonselective A1 and A2 adenosine receptor antagonist BWA-1433U significantly antagonizes vasoconstrictor responses of R-PIA and vasodilator responses of adenosine, 2-CADO, and R-PIA. These data support that adenosine produces vasoconstriction at low baseline PV tone and vasodilation at elevated PV tone in the feline PV bed by acting on A1 and A2 adenosine receptors, respectively. Compared with the adenosine receptor agonists tested in this in vivo model, R-PIA and CV-1808 are the most selective adenosine receptor agonists for A1 and A2 adenosine receptors, respectively, in the feline PV bed. R-PIA, CV-1808, DPCPX, and XAC may be used in this in vivo model to define the roles of A1 and A2 adenosine receptors in acute lung injury and pathophysiological changes in the pulmonary vasculature associated with pulmonary hypertension and edema formation in the same animal model.