Study on circadian changes in sympathetic tone in subtotal nephrectomized rats with heart failure

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We studied whether chronic kidney disease (CKD) could alter circadian changes in autonomic function in rats with heart failure (HF). Rats underwent subtotal nephrectomy and surgically induced myocardial infarction as a potential model of cardiorenal syndrome. After acclimatization to a 12h light-dark cycle, blood pressure, heart rate and locomotor activity were continuously recorded for 24 - 48 hours in conscious, unrestrained rats by using instrumented radiotelemetry pressure transducer. During the awakening period, low frequency components of diastolic blood pressure variability, an index of sympathetic tone, were more exaggerated in HF rats with CKD than in HF rats without CKD. Hypercapnic chemosensitivity evaluated by hourly intermittent CO2 exposure was transiently increased during the awakening period in HF rats with CKD, suggesting that central chemosensitivity could be related to the exaggerated sympathetic tone in cardiorenal syndrome.