Autonomic neuropathy precedes cardiovascular dysfunction in rats with diabetes.
BACKGROUND
Our team previously demonstrated arterial stiffening and cardiac hypertrophy in type 2 diabetic rats at 8 but not 4 weeks after being administered streptozotocin (STZ) and nicotinamide (NA). The present study focused on investigating the effects of type 2 diabetes on cardiac autonomic nerve function in the STZ- and NA-treated animals, using modern spectral estimation technique.


METHODS
An autoregressive process was performed to each detrended signal of heart rate and systolic blood pressure measured in the 4- and 8-week STZ-NA rats with anaesthesia. The power of low-frequency and high-frequency oscillations was automatically quantified with each spectral peak by computing the residuals. The closed-loop baroreflex gain was estimated using the square root of the ratio between heart rate and systolic blood pressure powers in the low-frequency band.


RESULTS
Compared with the age-matched controls, both the 4- and 8-week STZ-NA diabetic rats had significantly decreased low-frequency oscillations of heart rate but not systolic blood pressure variability, showing a decline in baroreflex gain (0.451 +/- 0.060 and 0.484 +/- 0.056 vs. 1.196 +/- 0.064 ms mmHg(-1), P < 0.05). On the other hand, the low frequency-high frequency power ratio of the heart period was also diminished in the two diabetic groups, indicating a shift in sympatho-vagal balance of the heart control (0.472 +/- 0.109 and 0.504 +/- 0.090 vs. 1.857 +/- 0.336, P < 0.05).


CONCLUSIONS
The cardiac autonomic dysfunction in the absence of any significant changes in vascular dynamics, 4 but not 8 weeks after induction of type 2 diabetes, suggests that the diabetic autonomic neuropathy may precede arterial stiffening and cardiac hypertrophy in the STZ- and NA-treated rats.
Department of Automatic Control Engineering, Feng-Chia University, Taichung, Taiwan.
Y-D
YD
Lin
K-L
KL
Hsu
E-T
ET
Wu
M-S
MS
Tsai
C-H
CH
Wang
C-Y
CY
Chang
K-C
KC
Chang
D000818:Animals; D001341:Autonomic Nervous System / Q000503:physiopathology*; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure; D006332:Cardiomegaly / Q000209:etiology / Q000503:physiopathology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000503:physiopathology*; D003925:Diabetic Angiopathies / Q000503:physiopathology*; D006339:Heart Rate; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013057:Spectrum Analysis / Q000379:methods