You can not induce Type-2 diabetics using Streptozotocin alone in adult rats. Please give High Fat Diet (Lard Conc 40-50%) for around 14 days. HFD should increase the body weight. On day 15 inject STZ, 45mg/kg in Citrate Buffer, i.p. route. At the end of 3rd week you can check fasting blood glucose levels. You have to standardise this method with some changes according to your facility. Try to standardise it on male rats, body weight range 140 to 160g (wistar or SD).
OR If you want to use only STZ then try in rat pubs (age within 24h of birth). Single shot of STZ (90-100mg/kg, i.p. route) will work. Allow the pubs with mother up to weaning period. Then check the fasting blood glucose level.
Freshly prepare streptozotocin solution in 0.1M citrate buffer, pH 4.5 and inject intraperitoneally (50mg/kgbw) to overnight starved rats. Check Fasting blood glucose and post prandial glucose (PPG) regularly till stable hyperglycaemia is established. Animals with stabilized diabetes having FBG equal to/more than 250 mg/dl were used
Apart from the answers given by Drs Hamza and Misra, we recently induced an animal model of type 2 diabetes using a new approache which has been published in the Pharmacological Reports on 2012 authored by Wilson RD and Islam MS. You can have a look on that paper which is accessible freely on the web or journal home page. Please let me know if you cannot get it from the web or journal any way.
We have done streptozotocin induced diabetes in our research. Many rats die from very high glucose, osmotic diuresis, and volume depletion are the underlying factors for the high mortality of streptozotocin induced diabetes. This is not a sustainable model to investigate long-term effects of diabetes on organ system. Her is our publication citation: Clin Exp Hypertens Theory and Practice 1990; A12: 1021-1035.
STZ can induce mild hyperglycaemia but in no way replicates the complex pathophysiology of T2DM. So I agree with Dr Misra, in some respects. However, the best models are the various rat strains available specifically as models of T2DM.
STZ induced diabetes and T2D are not comparable, as Dr. Smith states. Our research questions must be carefully formulated and possible approaches thoroughly thought through if we want to make sound conclusions. STZ is useful for killing beta cells, but it is a model of diabetes only in the most simplified sense, that beta cells are destroyed and blood glucose will rise.