Adenosine release in morphine-induced hypotension in rats.

1. Following intravenous administration of morphine.HCl a reduction in mean arterial blood pressure (MABP) was produced, quaternary morphine analogue was ineffective. 2. Theophylline and 8-phenyltheophylline administration reduced morphine-induced hypotension. 3. A2 adenosine receptor agonist caused an hypotension while A1 adenosine receptor agonist was ineffective. 4. L-NG-Mono-methylarginine administration reduced the hypotensive effect of exogenous A2 agonist while it was ineffective on morphine-induced hypotension. 5. Morphine-induced hypotension was increased by pretreatment with dipyridamole, whereas tetrabenazine abolished it. 6. The present study is consistent with previous reports on the central hypotensive action of morphine and propose a role for adenosine release in morphine-induced hypotension.