Intrapericardial capsaicin and bradykinin induce different cardiac-somatic and cardiovascular reflexes in rats

Patients with myocardial infarction experience various types of chest pain and autonomic disturbance symptoms. Studies in rats have shown that pericardial infusions of certain chemicals induce cardiac-related muscle pain and cardiovascular reflexes. In the present study, bradykinin or capsaicin was injected into the pericardial sac and the resulting cardiac-somatic reflexes and blood pressure (BP) alterations were record. We found that the cardiac-somatic reflex induced by bradykinin had a longer latency, shorter duration, and lower firing rate than that induced by capsaicin (p<0.05). We also found that bradykinin induced a hypertensive response (p<0.05), while capsaicin induced a hypotensive response (p<0.05). Bilateral vagotomy had no effect on the cardiac-somatic reflex induced by bradykinin (p>0.05) but reduced the reflex induced by capsaicin (p<0.05). However, vagotomy had no effect on the BP alterations induced by both bradykinin and capsaicin (p>0.05). These results suggest that bradykinin and capsaicin activate different pathways to induce cardiac-somatic and cardiovascular reflexes and that the vagus nerve is involved in TRPV1-related muscle pain modulation.