Effects of interleukin-6 treatment on neurovascular function, nerve perfusion and vascular endothelium in diabetic rats

Aim: Interleukin‐6 (IL‐6), a member of the neuropoietic cytokine family, participates in neural development and has neurotrophic activity. Recent research has also indicated actions to improve vasa nervorum function in diabetes. Both these facets are potentially relevant for treatment of diabetic neuropathy. The aim of this study was to determine whether IL‐6 treatment corrected changes in neurovascular function in streptozotocin‐induced diabetic rats. Methods: After 1 month of diabetes, rats were given IL‐6 for 1 month. The rats were subjected to sensory testing and measurements of nerve conduction velocities and nerve blood flow by hydrogen clearance microelectrode polarography. Further groups were used to study responses of the isolated gastric fundus and renal artery. Results were statistically analysed using ANOVA and post hoc tests. Results: Diabetic rats showed mechanical hyperalgesia, thermal hyperalgesia, and tactile allodynia. The former was unaffected by IL‐6 treatment, whereas the latter two measures were corrected. Immunohistochemical staining of dorsal root ganglia for IL‐6 did not reveal any changes with diabetes or treatment. The results showed that 22 and 17.4% slowing of sciatic motor and saphenous sensory nerve conduction velocities, respectively, with diabetes were improved by IL‐6. Sciatic endoneurial perfusion was halved by diabetes and corrected by IL‐6. A 40.6% diabetic deficit in maximal non‐adrenergic, non‐cholinergic relaxation of gastric fundus to nerve stimulation was unaffected by IL‐6. Renal artery endothelium‐dependent relaxation was halved by diabetes, the endothelium‐derived hyperpolarizing factor (EDHF) component being severely attenuated. IL‐6 did not affect nitric oxide‐mediated vasorelaxation, but markedly improved EDHF responses. Conclusions: IL‐6 improved aspects of small and large nerve fibre and vascular endothelium dysfunction in diabetic rats. The functional benefits related to increased nerve blood flow via an EDHF mechanism, and IL‐6 could have therapeutic potential in diabetic neuropathy and vasculopathy, which should be further evaluated.