Bioassay of Oxytocin

• Bioassay of Oxytocin: Commonly done using uterine contraction response in rats or guinea pigs.
• Bioassays of Oxytocin’s: Measures potency by comparing test sample to standard oxytocin.

Principle of Bioassay of Oxytocin

• Oxytocin stimulates rhythmic contraction of uterine smooth muscle and also causes milk ejection.
• The bioassay relies on measuring the uterine contraction magnitude or frequency induced by oxytocin.

Methods

1. Rat Uterus Assay (In Vitro)

• Procedure:
  1. Use an estrogen-primed rat (to ensure the uterus is sensitive to oxytocin).
  2. Isolate the uterine horns/strips and mount in an organ bath with physiological solution.
  3. Add standard oxytocin in graded doses, record contractions, wash out, then repeat with the test sample.
• Potency Determination: Plot dose-contraction curves for standard and test; the potency is determined by comparing ED50 values (the dose that produces 50

2. In Vivo Method (e.g., Anesthetized Cat or Rat)

• Procedure:
  1. Oxytocin is administered intravenously.
  2. Measure and compare uterine contractions against those produced by the standard.
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• Potency Determination: Compare the doses needed to produce a defined contraction response (e.g., 50

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