Relaxin treatment significantly suppressed sustained atrial fibrillation in spontaneously hypertensive rats (12.5% vs 100% in vehicle-treated SHR; P<0.01).
Does relaxin suppress atrial fibrillation and reverse fibrosis and myocyte hypertrophy in spontaneously hypertensive rat hearts?
Relaxin suppresses atrial fibrillation in spontaneously hypertensive rats by reversing fibrosis and hypertrophy and increasing conduction velocity and sodium current.
Absolute Event Rate: 12.5% vs 100%
p-value: p=<0.01
RATIONALE: Atrial fibrillation (AF) contributes significantly to morbidity and mortality in elderly and hypertensive patients and has been correlated to enhanced atrial fibrosis. Despite a lack of direct evidence that fibrosis causes AF, reversal of fibrosis is considered a plausible therapy. OBJECTIVE: To evaluate the efficacy of the antifibrotic hormone relaxin (RLX) in suppressing AF in spontaneously hypertensive rats (SHR). METHODS AND RESULTS: Normotensive Wistar-Kyoto (WKY) and SHR were treated for 2 weeks with vehicle (WKY+V and SHR+V) or RLX (0.4 mg/kg per day, SHR+RLX) using implantable mini-pumps. Hearts were perfused, mapped optically to analyze action potential durations, intracellular Ca²⁺ transients, and restitution kinetics, and tested for AF vulnerability. SHR hearts had slower conduction velocity (CV; P<0.01 versus WKY), steeper CV restitution kinetics, greater collagen deposition, higher levels of transcripts for transforming growth factor-β, metalloproteinase-2, metalloproteinase-9, collagen I/III, and reduced connexin 43 phosphorylation (P<0.05 versus WKY). Programmed stimulation triggered sustained AF in SHR (n=5/5) and SHR+V (n=4/4), but not in WKY (n=0/5) and SHR+RLX (n=1/8; P<0.01). RLX treatment reversed the transcripts for fibrosis, flattened CV restitution kinetics, reduced action potential duration at 90% recovery to baseline, increased CV (P<0.01), and reversed atrial hypertrophy (P<0.05). Independent of antifibrotic actions, RLX (0.1 µmol/L) increased Na⁺ current density, INa (≈2-fold in 48 hours) in human cardiomyocytes derived from inducible pluripotent stem cells (n=18/18; P<0.01). CONCLUSIONS: RLX treatment suppressed AF in SHR hearts by increasing CV from a combination of reversal of fibrosis and hypertrophy and by increasing INa. The study provides compelling evidence that RLX may provide a novel therapy to manage AF in humans by reversing fibrosis and hypertrophy and by modulating cardiac ionic currents.
Parikh et al. (Fri,) conducted a other in Atrial fibrillation. Relaxin (RLX) vs. Vehicle was evaluated on Sustained AF triggered by programmed stimulation (p=<0.01). Relaxin treatment significantly suppressed sustained atrial fibrillation in spontaneously hypertensive rats (12.5% vs 100% in vehicle-treated SHR; P<0.01).