causes hypotension by activating pulmonary sympathetic afferents in the rabbit. J Appl Physiol 95: 233-240, 2003. First published April 4, 2003 10.1152/japplphysiol.00584.2002 activates sympathetic afferents in the heart, intestine, and kidney, and it alters hemodynamics. However, we know little about the influence of pulmonary sympathetic afferents on circulation. Activation of pulmonary afferents by directly injecting stimulants into the lung parenchyma permits examination of reflexes that originate in the lung without confounding effects from the systemic circulation. In the present study, we tested the hypothesis that pulmonary sympathetic afferents exert a significant influence on hemodynamics. We examined reflex effects of injecting BK (1 g/kg in 0.1 ml) into the lung parenchyma on circulation in anesthetized, open-chest, artificially ventilated rabbits. BK significantly decreased mean arterial blood pressure (BP) (27 Ϯ 3 mmHg) and heart rate (19 Ϯ 4 beats/min). Both effects remained after bilateral vagotomy. To rule out possible direct systemic vasodilation by BK, we examined renal sympathetic nerve activity (RSNA) in response to BK injection and examined BP responses to injection of ACh (0.1 ml of 10 Ϫ4 M). BK suppressed the RSNA before and after vagotomy. ACh did not change BP when injected into the lung parenchyma, but it decreased BP (31 Ϯ 3 mmHg) when injected into the right atrium. Our data indicate that activating pulmonary sympathetic afferents reflexly suppresses hemodynamics. lung receptors; lung reflex; depressor effect; bradycardia FOR DECADES IT HAS BEEN RECOGNIZED that cardiovascular regulation is strongly influenced by inputs from the lung (24). These pulmonary inputs are believed to travel mainly in the vagus nerves. Mechanically activating pulmonary stretch receptors (33) or chemically activating pulmonary C fibers (4) in the vagus nerve can cause peripheral vasodilation and changes in heart rate. Activation of some pulmonary vagal afferents in the rabbit causes a slight pressor response in addition to stimulating breathing (25, 34). However, information regarding the reflex effects evoked from pulmonary sympathetic afferents is scarce and debatable (23).Sensory information in the lung is transmitted through vagal and sympathetic nerves (32). Morphological evidence points to the existence of sympathetic afferents in the lungs (13,18,22). Pulmonary sympathetic afferent activity has been recorded in stellate ganglia (9) and white rami of T 2