We performed a research regarding duration of diabetes. Diabetes mellitus was induced by injection of STZ (65 mg/kg, i.p). There were two period of diabetes in experimental animals; short term (2 week) and long term (6 week) diabetes. We obtained interesting results. There were no significant differences in serum insulin, SOD and LDH levels between groups. Is it possible? Is there any article which you see before about that? What do you think about these results?
Did your rats become diabetic to the extent you had wished? If yes, what were their fasting and ad lib fed blood glucose levels?
There are some strain-dependent differences in STZ dose to induce diabetes. In case of normal Wistar and Lewis rats (which are fairly common strains), a single intraperioneal injection of 65mg/kg STZ is unlikely to cause total destruction of all beta cells. If sufficient beta cells remain intact, they may be able to manage well enough. [I am assuming that STZ was delivered into peritoneum and not into any other organ.]
Yes, our rats (Sprague Dawley, 3-4 months old) becomes diabetic, fasting blood glucose levels was about 300-450 mg/dl. However, I could not find any article in literature which show no difference in insulin level between diabetic and healty rats.
Salih, the next obvious question that comes to mind is how are you measuring rat insulin? If you do not have sufficiently high sensitivity and dynamic range in your chosen method and all your readings are in the lower part of the curve (close to baseline), you may have difficulty in accurately quantitating insulin.
I am also of the same opinion as Dr. Tausif Alam. The insulin levels in normal rats are very low and in diabetic rats, they further decrease. Under such circumstance, it is very important to consider the sensitivity of ELISA kit used. The STZ model of diabetes is very reliable model and produces stable diabetes. There are several reports that it causes reduction in insulin levels.
Dear Salih,
The degree of beta cell destruction in STZ-induced diabetic rats varies depending on many thinks such as:
1- Age of rats; β-cells of younger animals are less sensitive to STZ (FBG levels in young rats: about 150 - 250, older rats: about 300 - 600 mg/dl)
2- Gender of rats
3- The strain of rats
4- Injection of STZ in fasting or fed rats
5- The dose of STZ used for induction of diabetes in rats (the solution should be made fresh)
6- Administration route of STZ in rats
7- Measuring blood glucose in fasting or ad libitum fed rats
If your rats became diabetic (FBG levels were about 300-450 mg/dl), it appears that measuring rat insulin (used method or Elisa kit) has difficulty.
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