Reflexes from pulmonary arterial baroreceptors in dogs: interaction with carotid sinus baroreceptors

Non‐technical summary Specialized nerve endings in the walls of various blood vessels are sensitive to alterations in the distending pressure. An increase in the blood pressure inside several arteries, including aorta, carotid and coronary arteries, generates sensory activity which causes reflex changes in the heart and circulation to reduce blood pressure. They operate as a negative feedback control and stabilise blood pressure. In this study we show that stimulation of pressure receptors in the walls of the pulmonary artery (low pressure) results in responses that differ from those originating from high pressure arteries. Instead of causing decreases in blood pressure and vascular resistance, their effect is to increase them. We also show that the effects on nervous activity to the kidney are different; stimulation of arterial receptors decreases renal nerve activity whereas stimulation of pulmonary arterial receptors increases it. There is interaction between the two reflexes. In other words, the level of stimulation of one reflex affects the responses from the other. We suggest that pulmonary arterial receptors are likely to have important physiological and pathophysiological consequences; they could contribute to causing the blood pressure increase during exercise as well as being involved in blood pressure control as the body changes orientation. They may also be involved in blood pressure control in heart failure and in the high pulmonary arterial pressures that are seen, for example, at high altitudes. In contrast to the reflex vasodilatation occurring in response to stimulation of baroreceptors in the aortic arch, carotid sinuses and coronary arteries, stimulation of receptors in the wall of pulmonary arteries results in reflex systemic vasoconstriction. It is rare for interventions to activate only one reflexogenic region, therefore we investigated how these two types of reflexes interact. In anaesthetized dogs connected to cardiopulmonary bypass, reflexogenic areas of the carotid sinuses, aortic arch and coronary arteries and the pulmonary artery were subjected to independently controlled pressures. Systemic perfusion pressure (SPP) measured in the descending aorta (constant flow) provided an index of systemic vascular resistance. In other experiments, sympathetic efferent neural activity was recorded in fibres dissected from the renal nerve (RSNA). Physiological increases in pulmonary arterial pressure (PAP) induced significant increases in