Influence of pH and pCO2 on Alpha‐Receptor Mediated Contraction in Brain Vessels

Abstract

The response of isolated brain vessels in the cat to various pH levels or CO2 tensions [PCO2] 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 the response was enhanced 3-fold at a pH of 7.80. Variations in CO2 tension of the buffer solution between 16 mmHg and 64 mmHg produced no consistent change, provided the pH remained constant. An interaction between the perivascular pH and the adrenergic .alpha.-receptor mediated contraction in brain vessels may occur.