Principle
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 of Oxytocin
Rat Uterus Assay (In Vitro)
Procedure:
Use an estrogen-primed rat (to ensure the uterus is sensitive to oxytocin).
Isolate the uterine horns/strips and mount in an organ bath with physiological solution.
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% of maximal effect).
In Vivo Method (e.g., Anesthetized Cat or Rat)
Procedure:
Oxytocin is administered intravenously.
Measure and compare uterine contractions against those produced by the standard.
Potency Determination: Compare the doses needed to produce a defined contraction response (e.g., 50% maximal).