Relationship between CSF and blood glucose concentrations in rats

Objective To explore the relationship between blood and CSF glucose concentration under the circumstance of stable blood glucose and blood glucose fluctuation, and modify current calculation of reference range for CSF glucose concentration. Methods SD rats were intraperitoneally injected with streptozotocin solution to construct diabetic rat model. Seventy normal rats were randomly divided into N+S group (n=35) and N+G group (n=35). Rats in N+S group received intraperitoneal injection of normal saline (20 ml/kg), while N+G group received intraperitoneal injection of 10% glucose solution (20 ml/kg). Seventy diabetic rats were randomly divided into D+S group (n=35) and D+G group (n=35). Rats in D+S group received intraperitoneal injection of normal saline (20 ml/kg), while D+G group received intraperitoneal injection of 10% glucose solution (20 ml/kg). At 45 and 15 minutes prior to the administration of glucose solution/ normal saline, and 15, 45, 75, 105, 135 minutes after the administration, CSF and blood samples were collected from 5 rats per group, and CSF and blood glucose concentration were measured. Results For N+S group and D+S group, there was a linear relationship between blood and CSF glucose concentration (N+S group, r=0.943, P=0.000; D+S group, r=0.866, P=0.000). For N+G group and D+G group, there was a 60 min time lag of glucose peaking time in CSF compared to blood. There was also a linear relationship between CSF glucose and average blood glucose level during 60 min prior to CSF collection (N+G group, r=0.964, P=0.000; D+G group, r=0.993, P=0.000). Conclusion For rats with stable blood glucose level, blood glucose measured at any time points can be the reference for CSF glucose. For rats with a fl uctuated blood glucose level, there is a time lag for CSF glucose, which can be calculated based on the average of blood glucose level during 60 min prior to CSF glucose measurement.