How do you explain that 3 days after injection of streptozotocin to rats, they have 16h fasting blood and glucose levels above 15 mmol/l? 10 days after some of these rats have 16h fasting blood glucose level of about 6 mmol/l, although their non fasting blood glucose level still above 18 mmol/l.
There are two points to be considered, one is it depends on the dose of streptozotocin given and whether the injection is given properly given that streptozotocin has a short half life and secondly these rats are normal rats and the process of beta cell regeneration is also initiated. Hence after 15 days some of them would show recovery in fasting blood glucose but they still have impaired glucose metabolism and hence demonstrate higher non-fasting blood glucose. To prevent this you can start giving glucose infusions or put the rats on high fat diet so that they turn into confirmed diabetic rats
It has happened to me before maybe you have to re inject them again by increasing the dose or you use another diabetology toxin like alloxan or you use diet or fructose
This is very common! If you conduct dose response curves for the effect of a single dose of STZ the clinical response will range from death through complete beta cell death to a range of degrees of beta cell death to no effect on beta cells. There is an acute effect but some beta cells recover. At the time point you mention there would not have been time for beta cell hypertrophy/neogenesis. So your dose is not killing all beta cells and those that survive have a headache for a while and then recover! In essence your animals have impaired glucose tolerance due to a reduced beta cell mass. This can be difficult to achieve intentionally as STZ can be tricky to use reproducibly due the the many variables that affect its efficacy. Other protocols may help but what matters is understanding and controlling the variables that affect beta cell death following STZ administration.
Hope this makes sense!
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