The influence of long term voluntary exercise on cardiac autonomic function in conscious chronic kidney disease animals

Background: Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular morbidity and mortality. Exercise has enduring cardio-protective effects that arise, in part, as a result of improved autonomic control of heart rate (HR). The aim of our study was to determine if voluntary exercise improves autonomic function in conscious animals with CKD, specifically examining the balance between sympathetic and parasympathetic cardiac tone. Methods: Mixed sex Lewis and Lewis polycystic kidney disease (LPK) rats were used. Animals were divided into four groups: sedentary Lewis (SL) (n=4); exercise Lewis (EL) (n=3); sedentary LPK (SLPK) (n=2); and exercise LPK (ELPK) (n=2). The exercise group was provided unlimited access to an activity wheel in their home cage from 5 weeks of age, and the sedentary group a locked activity wheel. At 10 weeks of age, rats were implanted with radio-telemetry probes. At 13 weeks, resting HR, mean blood pressure (MBP) and activity were determined over a 20 minute period during the day and changes in HR in response to atenolol (AT, 1 mg/kg i.p.) and methylatropine (MA, 2 mg/kg, i.p.). Results: Resting HR and activity was not significantly different between any groups. MBP was higher in both ELPK and SLPK compared with Lewis (average: 213.4 ± 3.8 vs. 96.8 ± 2.8 mmHg, P<0.05). In the ELPK compared to SLPK, atenolol produced a smaller reduction in HR (-47.5 ± 0.8 vs. -66.9 ± 2.8 bpm, P<0.05) and methylatropine a greater increase in HR (85.8 ± 5.3 vs. 54.9 ± 5.1 bpm, P<0.05) indicating a relative reduction in sympathetic and increase in vagal tone in the exercised animals. This was not observed in the Lewis rats. Conclusion: Our preliminary data demonstrates that exercise promotes vagal control of HR in rodents with CKD. Future studies will identify if this translates to an improvement in baroreflex control of HR.