Independent association between plasma leptin levels and heart rate in heart transplant recipients

Background-Leptin, the protein product of the ob gene, has been linked to a faster heart rate in animal and human studies. The interaction between lep tin and heart rate in the denervated heart is not known. Therefore, we stud ied the relationship between plasma leptin levels and heart rate in heart t ransplant recipients. Methods and Results-We studied 32 male patients (mean age, 56.5 +/-9.3 year s; range, 41 to 74 years) after orthotopic heart transplantation. All subje cts underwent a physical examination, anthropometric measurements, blood ch emistry analysis, and office blood pressure measurements. A blood sample wa s collected from each subject while fasting. In univariate analysis, heart rate was related to leptin levels (r=0.47, P=0.007) but heart rate was not related to systolic or diastolic blood pressure, mean arterial pressure, bo dy mass index, or catecholamines. Leptin levels were only strongly associat ed with heart rate and body mass index (r=0.73, P<0.0001). In multivariate analysis, heart rate was independently and positively associated with lepti n levels (F=2.61, P=0.017). We also observed a strong, independent associat ion between leptin levels and body mass index (F=5.8, P<0.00001). Conclusions-We show an independent association between leptin levels and he art rate in heart transplant recipients. We speculate that this may be due, in part, to a direct effect of leptin on heart rate, conceivably mediated through cardiac leptin receptors.