Evidence for purinergic receptors on vascular smooth muscle in rat pancreas.

The changes in flow rate in the isolated pancreas of the rat in response to natural purine nucleotides and phosphate-modified analogues were recorded. ATP and ADP transiently decreased the flow rate in a dose-dependent manner but only at very high concentrations (greater than 165 microM). In contrast, alpha,beta-methylene ATP, the most active of the drugs used, decreased the flow rate of the preparation at very low concentrations: 0.495 microM induced about 50% of the maximum effect. beta, gamma-Methylene ATP and AMP-PNP had an intermediary potency. Pyrophosphate had no effect. AMP and adenosine had no vasoconstrictor effect even at 1650 microM. The vasoconstrictor effect of alpha,beta-methylene ATP was not antagonized by phenoxybenzamine (6 microM) or by apamin (0.01 microM). In contrast PIT, a P2-purinergic receptor antagonist, partially or totally blocked the alpha,beta-methylene ATP effect depending on the concentrations used. From our results it can be concluded that purinergic receptors of P2-type are present on the vascular smooth muscle of the pancreatic bed in the rat.