Effect of drugs on the force of spontaneous mechanical activity in rat portal vein.

A study was made on the force of spontaneous mechanical activity in the rat portal vein. Prostaglandin inhibitor, sodium meclofenamate, phosphodiesterase inhibitors, aminophylline and dipyridamole, adenosine and blockade of calcium entry by isoptin all reduced the force of spontaneous activity in a concentration-dependent manner, while imidazole enhanced it. Low concentration of aminophylline (10 microM), dipyridamole (6 microM) and meclofenamate (10 microM) depressed the spontaneous contraction of the vein by about 50% without modifying the response to noradrenaline. At higher concentration of these drugs, spontaneous mechanical contraction was reduced further and the response to noradrenaline antagonized. Low concentration of isoptin also reduced the mechanical activity without affecting maximum response to noradrenaline. A common mechanism of action for the drugs tested, namely the limiting of Ca2+ availability for muscular contraction, is discussed. Adenosine markedly reduced the spontaneous mechanical activity of the rat portal vein. Its relaxation effect could be due to the activation of a specific adenosine receptor.