Monitoring of glycemic status should begin when NOD mice reach 10 weeks of age. Generally, this is done at weekly intervals by using Diastix (Bayer Diagnostics; appendix 5) or similar reagent strips to measure urine glucose. Picking a mouse up leads to immediate urination, allowing a drop to be collected on the test area (tip) of the reagent strip. High levels of glucose in the urine (glycosuria) appear when plasma glucose is >300 mg/dl. A nonfasting plasma glucose of >300 mg/dl for 2 consecutive weeks indicates IDDM. The nonfasting plasma glucose levels of young, prediabetic NOD mice ranges between 130 and 180 mg/dl. Plasma glucose can be measured directly in small samples of venous blood using glucose oxidase methods (either commercially available glucose analyzers or small portable analyzers and glucose oxidase-coated test strips; see unit 15.3 for details). Onset of IDDM can also be accelerated in young prediabetic NOD mice by intraperitoneal administration (unit 1.6) of cyclophosphamide (Sigma; 200 to 300 mg per kg body weight). It is quite difficult to maintain hyperglycemic NOD mice by insulin treatment; mice are usually euthanized after the diagnosis is certain. Transition from mild to severe hyperglycemia occurs over a period of 3 to 4 weeks. During this time, the mouse will survive without insulin therapy. If insulin therapy is part of the investigator's experimental protocol, doses of 1 to 2 U of a 1:1 mixture of regular and slower-acting porcine insulin (both available from Novo Nordisk; appendix 5) are injected intraperi-toneally as required by empirical determination of hyperglycemic status immediately before injection in the morning and evening (also see unit 15.3).
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