How much glucose to inject into a rat? - briefly
For a 250 g rat, inject 0.5 ml of a 20 % glucose solution (≈1 g kg⁻¹); dosage should be scaled proportionally to the animal’s weight, typically remaining within 0.5–2 g kg⁻¹ for acute supplementation.
How much glucose to inject into a rat? - in detail
Determining the correct glucose volume for a laboratory rat requires consideration of body weight, desired plasma glucose increase, solution concentration, and injection route.
The calculation begins with the animal’s mass, typically expressed in grams. An average adult rat weighs 250–300 g; juvenile specimens may be 100–150 g. Desired plasma glucose elevation is commonly set at 50–100 mg/dL above baseline, corresponding to an increase of approximately 0.5–1 mmol/L.
The formula for the required glucose amount (mg) is:
• required mg = target increase (mg/dL) × blood volume (mL) ÷ 100
Blood volume in rats averages 6–7 % of body weight (≈ 0.06 × weight (g)). For a 250 g rat, blood volume ≈ 15 mL. To raise glucose by 80 mg/dL:
required mg = 80 × 15 ÷ 100 = 12 mg.
Next, select a glucose solution concentration. Commonly used preparations are 5 % (50 mg/mL) or 20 % (200 mg/mL) dextrose. Using a 5 % solution, the volume needed is:
volume (mL) = required mg ÷ concentration (mg/mL) = 12 ÷ 50 = 0.24 mL.
For a 20 % solution, the volume reduces to 0.06 mL.
Administration routes include intraperitoneal (IP) and intravenous (IV). IP injection is standard for short‑term glucose loading; the volume should not exceed 0.5 mL to avoid discomfort. IV injection, typically via the tail vein, allows precise control of plasma levels; volumes are generally limited to 0.1 mL.
Safety considerations:
• Verify sterility of the glucose solution; filter if prepared in‑house.
• Use isotonic saline as diluent when higher concentrations are required to prevent osmotic injury.
• Monitor blood glucose at 5‑minute intervals for the first 30 minutes, then at 15‑minute intervals for an additional hour.
• Adjust subsequent doses based on measured glucose values to maintain target levels.
Reference guidelines from the American Physiological Society and the National Institutes of Health recommend the above methodology for acute glucose challenges in rodents.
In practice, for a 250 g rat, an IP injection of 0.2–0.3 mL of 5 % dextrose reliably produces a transient plasma glucose rise of 80 mg/dL, while an IV dose of 0.05–0.07 mL of 20 % dextrose achieves a comparable effect with greater precision.