THE ROLE OF ADENOSINE IN THE HYPOTENSIVE ACTIONS OF MORPHINE

The role of adenosine in the hypotensive action of morphine was examin ed in the pentobarbitone anaesthetized or pithed rat preparations. Ade nosine (10-300 mu g/kg) induced dose-dependent decreases in diastolic blood pressure in the anaesthetized rat preparation. These effects wer e attenuated by infusion of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 50 mu g/kg/min), 8-phenyltheophylline (8PT; 50 mu g/kg/min), and 3,7- dimethyl-1-propargylxanthine (DMPX; 50 mu g/kg/min). In this preparati on morphine (10-1000 mu g/kg) also induced dose-dependent decreases in diastolic blood pressure. Guanethidine (16 mu g/kg/min), atropine (1 mg/kg), DPCPX and 8PT reduced the effect of morphine on diastolic bloo d pressure, whilst DMPX (50 mu g/kg/min) was inactive. In the pithed r at preparation morphine was inactive at doses up to 10 mg/kg. The resu lts suggest that the hypotensive effect of morphine is mediated at lea st in part by the release of adenosine which then acts on centrally lo cated adenosine receptors to induce changes in autonomic control of bl ood pressure.