Effect of pH changes on reactivity of rat mesenteric artery segments at different magnitude of stretch

The reaction to noradrenaline (NA) (10 muM) and electrical field stimulation (EFS) was studied in rat mesenteric artery segments at different magnitude of stretch and the solution pH. Alkaline solution (pH 7.8) potentiated and acidic solution (pH 7.0 or 6.6) inhibited the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 5-200 mmHg. These pH changes failed to alter resting tension at any magnitude of stretch. Acedic solution of pH 6.6 caused 2-fold decrease in noradrenaline- and 5-15-fold decrease in the EFS-evoked response of segments stretched to values corresponding to arterial pressure of 50, 125, and 200 mmHg. In segments pre-contracted with noradrenaline (10 muM) acidification caused the decrease of the dilation and appearance of the constriction induced by the EFS. The effect of acidosis on the EFS-evoked response was diminished and the effect on noradrenaline-evoked response was abolished in the presence of nitric oxide synthase blocker, N(G)-nitro-L-arginine (100 muM). These results suggest that acidosis effectively impairs reactivity of the rat mesenteric artery in a wide range of its stretch, and the inhibition of the response to noradrenaline occurs completely, while to EFS only partially due to nitric oxide NO) release, presumably by the endothelium. In addition, it was shown that acidosis is able to act not only as the commonly known dilator agent, but also as an agent potentiating constriction in case of the high noradrenaline-induced tone.