Insulin‐induced hypoglycemia directly affects the cerebral microvasculature in vivo

Abstract

ObjectiveInsulin therapy for patients with diabetes mellitus (DM) carries the risk for acute hypoglycemia (HG). Evidence from human and animal studies has suggested a role for HG in the exacerbation of cardiovascular dysfunction accompanying DM. Specifically, animal studies have shown that recurrent HG promotes increased ischemic brain injury. Furthermore, HG has been shown to affect mitochondrial function in cultured endothelial cells. Therefore, we hypothesized that acute insulin‐induced HG directly affects the cerebral microvascular function in vivo.MethodsWild type C57Bl/6 mice were prepared for long term two‐photon microscopy by removing a 4mm diameter section of bone over the somatosensory cortex which was then sealed with a glass coverslip held in place with cyanoacrylate and dental acrylic. A custom titanium bar was added to the preparation for head fixation during imaging. During imaging sessions, the cerebral vasculature was visualized using FITC‐dextran 40kDa. Mice were imaged under hypoglycemia (63.2 +/− 8.2 mg/dL by imaging start) using 1–2 U/kg of Humulin‐R. Microvessels approximately 3–5μm in diameter were measured for diameter changes using ImageJ. Blood flow through cerebral microvessels was assayed using line scans over the vasculature to determine red blood cell (RBC) traffic and speed. Fluorescence intensity was also measured in ImageJ to determine any changes in BBB permeability.ResultsAcute hypoglycemia induces a vasodilatory effect in cerebral microvasculature (diameter increased by 10.0 +/− 1.7 %, N=7 mice, n=89 microvessels, vs. 1.751 +/− 1.0 % N=6 mice, n=134 microvessels, in saline controls, p = .0007). However, blood flow was not changed between groups (149.0 +/− 7.4 vs. 167.6 +/− 11.3 RBC/sec and 0.979 +/− 0.060 vs. 1.052 +/− 0.068 μm/ms). Additionally, acute hypoglycemia caused no noticeable changes in the permeability of the BBB indicated by the extravasation of FITC‐dextran.ConclusionsOur data show that acute HG causes noticeable changes in the in vivo cerebral microvasculature, however, we did not note any changes in blood flow, potentially due to cerebral auto regulation. We therefore conclude that insulin‐induced HG causes noticeable direct effects on the cerebral vasculature that may play a role in cerebro vascular impairments in DM.Support or Funding InformationNational Institute of Health: National Institute of General Medical Sciences, National Institute of Aging, and National Institute of Neurological Disorders and Stroke (Mostany: R01AG049821; Katakam: R01NS094834).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.