α-Lipoic acid treatment prevents the diabetes-induced attenuation of the afferent limb of the baroreceptor reflex in rats

Autonomic neuropathies, common complications of prolonged diabetes, may result from diabetes-induced increased oxidative stress. Recently, we found that the afferent component of the baroreceptor reflex is attenuated in streptozotocin-induced diabetic rats. This study sought to determine the influence of the anti-oxidant, α-lipoic acid on the diabetes-induced deficits of the afferent limb of the baroreceptor reflex and on plasma malondialdehyde (a measure of lipid peroxidation). The number of c-Fos-ir neurons in the nucleus tractus solitarius in response to phenylephrine-induced baroreceptor activation was used as an index of the integrity of the afferent limb of the baroreceptor reflex. Groups of streptozotocin-induced diabetic and non-diabetic control rats, maintained from 8 to 16 weeks, were treated with α-lipoic acid (100 mg kg−1 IP, 5×/week), or vehicle for the last 4 weeks prior to the experimental procedure. Vehicle-treated diabetic rats had elevated plasma malondialdehyde levels when compared to non-diabetic rats. α-Lipoic acid-treated diabetic rats had plasma malondialdehyde levels similar to those seen in non-diabetic rats and less than those of vehicle-treated diabetic rats at both the 8- and 16-week time points. α-Lipoic acid treatment did not affect the baseline (absence of baroreceptor activation) presence of c-Fos-ir in the nucleus tractus solitarius. In response to phenylephrine and regardless of treatment, the diabetic and control rats displayed increases in blood pressure and reflex bradycardia. As previously reported, phenylephrine-induced baroreceptor activation resulted in significantly fewer c-Fos-ir neurons in the nucleus tractus solitarius (commissural and caudal subpostremal regions) of diabetic rats when compared to non-diabetic rats at both 8- and 16-week time points. Four weeks of α-lipoic acid treatment reversed the diabetes-induced decrement in the numbers of c-Fos-ir neurons in the nucleus tractus solitarius in response to baroreceptor activation. α-Lipoic acid-treated diabetic rats showed the same phenylephrine-induced c-Fos response in the nucleus tractus solitarius as those of α-lipoic-acid- and vehicle-treated control rats at both 8- and 16-week time points. These data suggest that diabetes-induced oxidative stress plays a role in diabetes-induced baroreceptor dysfunction and that the α-lipoic acid may have a beneficial effect in treatment of diabetic autonomic neuropathy.