Cross talk between renal and cardiac autonomic nerves: is this how renal denervation works?

Testosterone does not shorten action potential duration in Langendorff-perfused rabbit ventricles

BACKGROUND

Women have longer baseline QT intervals than men. Because previous studies showed that testosterone and 5α-dihydrotestosterone shorten the ventricular action potential duration (APD) in animal models, differential testosterone concentrations may account for the sex differences in QT interval.

OBJECTIVE

The purpose of this study was to test the hypothesis that testosterone shortens the APD in Langendorff-perfused rabbit ventricles.

METHODS

We performed optical mapping studies in hearts with or without testosterone administration. Acute studies included 26 hearts using 2 different protocols, including 17 without and 9 with atrioventricular (AV) block. For chronic studies, we implanted testosterone pellets subcutaneously in 7 female rabbits for 2-3 weeks before optical mapping studies during complete AV block. Six rabbits without pellet implantation served as controls.

RESULTS

The hearts in the acute studies were paced with a pacing cycle length (PCL) of 200-300 ms and mapped at baseline and after administration of 1 nM, 10 nM, 100 nM, and 3 μM of testosterone. There was no shortening of APD80 at any PCL. Instead, a lengthening of APD80 was noted at higher concentrations. There were no sex differences in testosterone responses. In chronic studies, heart rates were 136 ± 5 bpm before and 148 ± 9 bpm after (P = .10) while QTc intervals were 314 ± 9 ms before and 317 ± 99 ms after (P = .69) testosterone pellet implantation, respectively. Overall, ventricular APD80 in the pellet group was longer than in the control group at 300- to 700-ms PCL.

CONCLUSION

Testosterone does not shorten ventricular repolarization in rabbit hearts.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Renal sympathetic denervation for treatment of ventricular arrhythmias: a review on current experimental and clinical findings

Ventricular arrhythmias (VAs) remain the major cause of mortality and sudden cardiac death (SCD) in almost all forms of heart disease. Despite so many therapeutic advances, such as pharmacological therapies, catheter ablation, and arrhythmia surgery, management of VAs remains a great challenge for cardiologists. Evidence from histological studies and from direct nerve activity recordings have suggested that increased sympathetic nerve density and activity contribute to the generation of VAs and SCD. It is well known that renal sympathetic nerve (RSN), either afferent component or efferent component, plays an important role in modulation of central sympathetic activity. We have recently shown that RSN activation by electrical stimulation significantly increases cardiac and systemic sympathetic activity and promotes the incidence of acute ischemia-induced VAs, suggesting RSN has a role in the development of VAs. Initial experience of RSN denervation (RDN) in patients with resistant hypertension showed that this novel and minimally invasive device-based approach significantly reduced not only kidney but also whole-body norepinephrine spillover. In addition, experimental studies find that left stellate ganglion nerve activity is significantly decreased after RDN. Based on these observations, it is reasonable to conclude that RDN may be an effective therapy for the management of VAs. Indeed, RDN has provided a protection against VAs in both animal models and patients. In this article, we review the role of the RSN in the generation of VAs and SCD and the role of RDN as a potential treatment strategy for VAs and SCD.