Reduction of heart rate, but not heart rate variability, in diabetic rats

Abstract

Reduction of heart rate is an early event in type 1 diabetes mellitus (DM) in a number of species including rats, rabbits, and humans. This reduction has been attributed to baroreflex dysfunction resulting from increased parasympathetic tone (McDowell et al AJP 1994; 266: H235). DM was induced by streptozotocin in Long Evans rats (intact, n=5 & DM n=7). Systolic pressure did not differ between the groups. 24h average heart rate declined from 362 ± 4 at control to 356 ± 3 at week 3 and 346 ± 4 min−1 at week 11 in intact rats and from 370 ± to 328 ± 6 and 300 ± 6 min−1 in DM (decline p < 0.00003 versus intact). However, heart rate variability, expressed as coefficient of variation, was unchanged. We had previously shown that spectral analysis of blood pressure from heart rate (~6 Hz) to circadian (0.0000115 Hz) readily detects the roughly fivefold increase in blood pressure (BP) spectral power induced by chemoreceptors‐sparing partial baroreceptor denervation. This increase occurs only in the interval from 0.08 Hz out to 0.0004 Hz. Here we used spectral analysis of inter‐beat interval (one hour record) and of BP to compare intact and DM rats at the three time points. Repeated measures ANOVA was used to compare intact and DM rats in the frequency band noted above and in standard very low frequency (0.02 ‐ 0.2 Hz), low frequency (0.2 ‐ 0.6 Hz), and high frequency (0.6 ‐ 3 Hz) bands. As expected there were no differences between groups in the control condition. However there were also no differences between the intact and DM rats at weeks 3 and 11. To the extent that this analysis probes arterial baroreflex is, we can detect no differences between intact and diabetic rats. Funded by Heart & Stroke Fdn of BC & Yukon