Endothelin Modulates Rhythm Disturbances and Autonomic Responses to Acute Emotional Stress in Rats

SIMPLE SUMMARY: Our body’s reaction to acute emotional stress differs, depending on several factors, which include a small molecule called endothelin. Excessive responses are important, as they can trigger (sometimes serious) heartbeat disturbances. To further investigate the role of endothelin in this process, we compared the reactions to laboratory-induced stress in two groups of rats, known to have diverse baseline levels of endothelin in the blood. We found distinct responses leading to slow heartbeat disturbances in the latter group. This feature resembles that observed in people with a tendency to faint after strong emotions, a common problem with many unknown aspects. Our study calls for further research on the effects of endothelin on fainting and irregular heartbeat after acute emotional stress. ABSTRACT: The ubiquitous peptide endothelin is currently under investigation as a modulatory factor of autonomic responses to acute emotional stress. Baseline plasma levels of endothelin alter blood pressure responses, but it remains unclear whether autonomic activity and arrhythmogenesis (i.e., brady- or tachyarrhythmias) are affected. We recorded sympathetic and vagal indices (derived from heart rate variability analysis), rhythm disturbances, voluntary motion, and systolic blood pressure after acute emotional stress in conscious rats with implanted telemetry devices. Two strains were compared, namely wild-type and ET(B)-deficient rats, the latter displaying elevated plasma endothelin. No differences in heart rate or blood pressure were evident, but sympathetic responses were blunted in ET(B)-deficient rats, contrasting prompt activation in wild-type rats. Vagal withdrawal was observed in both strains at the onset of stress, but vagal activity was subsequently restored in ET(B)-deficient rats, accompanied by low voluntary motion during recovery. Reflecting such distinct autonomic patterns, frequent premature ventricular contractions were recorded in wild-type rats, as opposed to sinus pauses in ET(B)-deficient rats. Thus, chronically elevated plasma endothelin levels blunt autonomic responses to acute emotional stress, resulting in vagal dominance and bradyarrhythmias. Our study provides further insights into the pathophysiology of stress-induced tachyarrhythmias and syncope.