Microspheres cause release of prostac yclin but not adenosine in the bronchial circulation of intact sheep

We previously found that injection of 15 μ microspheres (MS) into the bronchial artery (BA) of sheep caused vasodilation that could be partially inhibited by indomethacin or 8-phenyltheophylline, an adenosine receptor antagonist (Am I Physiol 38:H1037, 1995). To measure directly release of prostaglandins and adenine nucleotides in the bronchial circulation we perfused the BA with a constant flow of blood in 3 anesthetized sheep. BA blood samples were obtained from the BA cannula by interrupting forward flow and transiently increasing left atrial pressure to promote retrograde BA flow. BA blood was obtained before and after injection of Ix10⁶ MS (n=7 injections) or MS diluent (n=4 injections). Plasma 6-keto-prpstaglandin F_1α (metabolite of prostacyclin) arid adenine nucleotides were measured by GC mass spectroscopy and HPLC. Microspheres Diluent ΔPba (mmHg) -59±5* -5.6±6 Δ6-keto-PGF_1α (pg/ml) 300±180* -40±50 ΔAdenosine (μmol/L) -0.44±0.44 0.90±0.41 Inosine and hypoxanthine were also not different. Moreover, the infusion of dipyridamole, an adenosine uptake inhibitor, did not alter the MS-induccd vasodilation or plasma adenosine levels suggesting that adenosine was not involved. We conclude that MS caused release of prostacyclin in the bronchial circulation of intact sheep.