Influence of pH and pCO2 on alpha-receptor mediated contraction in brain vessels.

The response of isolated brain vessels to various pH levels or carbon dioxide tensions was analyzed. Reduction of the pH induced a slight relaxation of the vessel, whereas an increase in the pH produced a slight contraction. These effects were markedly exaggerated when the alpha-adrenergic receptors in the vascular wall were activated by noradrenaline. During these conditions the contractile response to noradrenaline was reduced by about 40% at a pH of 7.01, while, on the other hand, the response was enhanced 3-fold at a pH of 7.80. Variations in carbon dioxide tension of the buffer solution between 16 mmHg and 64 mmHg produced no consistent change, provided the pH remained constant. The results indicate that an interaction between the perivascular pH and the adrenergic alpha-receptor mediated contraction in brain vessels may occur.