Pulmonary Spinal Sympathetic Afferent Activation in Post-myocardial Infarction Rats

Recently, we reported activation of pulmonary spinal afferents by topical application of bradykinin (BK) to lung surfaces evokes a potent sympatho-excitatory reflex, including increased blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in urethane-α-chloralose anesthetized vagotomized rats. This finding suggests a new previously undocumented pulmonary sympathetic afferent reflex (PSAR). Preliminary data was reported in abstract form at the Association of University Anesthesiologists 64 th Annual meeting. Expanding this work, we examined the activation of the PSAR at different time points post myocardial infarction (1 month vs. 5 months post MI) and at different degrees of infarct size (15%-35% (moderate) vs. above 35% (large) of left ventricle). Following bilateral vagotomy, we applied filter paper (3 х 3 mm) saturated with BK (10 μg/ml) to the ventral lung surface to stimulate the PSAR in both urethane- α-chloralose anesthetized sham-operated and MI rats. Application of BK to the lungs resulted in increased BP, HR and RSNA in all sham and MI rats. Compared to sham rats, the BK-induced sympatho-excitatory response was significantly increased in 1-month moderate and 1-month large MI rats as well as in 5-month moderate MI rats. The BK-induced sympatho-excitatory response was significantly blunted in 5-month large MI rats (Table 1). These data suggest that the activation of pulmonary spinal afferents in the post-MI state may be an independent risk factor for sympatho-excitation. Further studies are needed to understand the differential effects of pulmonary spinal afferent activation at the transition from the post MI state to heart failure.