Vascular responses to catecholamines during respiratory changes in pH.

The influences of hypercapnia and hyperventilation on peripheral vascular responses to adrenaline and noradrenaline were observed in lightly anesthetized dogs. Changes in the carotid artery blood flow and pressure induced by intra-arterial doses of these amines were measured before, during and after the respiratory changes. During hypercapnia and low blood pH there was a reduced peripheral vascular response, while during hyperventilation and a high pH the vascular response to these drugs increased. However, a fall in blood pressure and flow, and a reflex elevation of the peripheral resistance occurred during both the hyperventilation and the posthypercapnic periods. It appeared that the elevated responses to the amines during those periods of high vasomotor tone may have been produced, in part at least, by the geometric factors involved in resistance, and not entirely by an increased response of the vascular smooth muscle.