Long-term effects of type 2 diabetes mellitus on heart rhythm in the Goto-Kakizaki rat

First published online on December 21, 2007.
Experimental Physiology (2007)
DOI: 10.1113/expphysiol.2007.040055
Frank Christopher Howarth 1*, Michael Jacobson 2, Mohamed Shafiullah 1, Ernest Adeghate 1
1 United Arab Emirates University
2 Higher Colleges of Technology
* To whom correspondence should be addressed. E-mail: chris.howarth@uaeu.ac.ae.
In vivo biotelemetry studies have demonstrated a variety of heart rhythm disturbances in type 1 diabetes mellitus. In the streptozotocin (STZ) iV induced diabetic rat these disturbances have included reductions in heart rate (HR) and heart rate variability (HRV) and an electrocardiogram (ECG) that displays prolonged QRS duration and Q-T interval. The aim of this study was to investigate the chronic effects of type 2 diabetes mellitus on heart rhythm in the Goto-Kakizaki (GK) rat. Transmitter devices were surgically implanted in the peritoneal cavity of young male GK and age-matched Wistar control rats. Electrodes from the transmitter were arranged in Einthoven bipolar ¡V Lead II configuration. ECG, physical activity and body temperature data were recorded in rats from age 2 to 15 months. Data was acquired for 2 weeks each month. Non-fasting blood glucose and body weight were measured periodically and a glucose tolerance test was performed during the last month of the experiment. Growth rate and maximal attained body weight were significantly reduced and non-fasting blood glucose was progressively increased in GK rats compared to age-matched controls. HR was significantly lower in GK rats compared to controls at 2, 7 and 15 months of age. At 2 months of age HR was 316±6 beats per minute (BPM) in GK rats compared to 370±7 BPM in controls. There was a progressive age-dependent decline in HRV in control rats however, HRV in GK rats did not alter significantly with age. HRV was significantly reduced in GK rats compared to controls at 2 and 7 months. At 2 months of age HRV was 28±2 BPM in GK rats compared to 38±3 BPM in controls. Reduced HR and HRV and changes in HRV with time in GK rats compared to age-matched controls may be associated with a progressively developing autonomic neuropathy.