Short-term effects of streptozotocin-induced diabetes on the electrocardiogram, physical activity and body temperature in rats

A variety of contractility defects have been reported in the streptozotocin (STZ)-induced diabetic rat heart including alterations to the amplitude and time course of cardiac muscle contraction. Transmitter devices were surgically implanted in the peritoneal cavity of young adult male Wistar rats. Electrodes from the transmitter were arranged in Einthoven bipolar lead II configuration. Electrocardiogram (ECG), physical activity and body temperature data were continuously recorded with a telemetry system before and following the administration of STZ (60 mg kg^-1). Heart rate (HR), physical activity and body temperature declined rapidly 3-5 days after administration of STZ. The effects became more conspicuous with time and reached a new steady state approximately 10 days after STZ treatment when HR was 255 ± 8 beats min^-1 in diabetic rats compared to 348 ± 17 beats min ^-1 in age-matched controls. Heart rate variability (HRV) was also significantly reduced after STZ treatment (18 ± 3 beats min^-1) compared to controls (36 ± 3 beats min^-1). Reduced physical activity and/or body temperature may partly underlie the reduction in HR and HRV. Reductions in power spectral density at higher frequencies (2.5-3.5 Hz) suggest that parasympathetic drive to the heart maybe altered during the early stages of STZ-induced diabetes. Short-term diabetes-induced changes in vital signs can be effectively tracked by continuous recording using a telemetry system.