A Sensitivein VitroAssay for Oxytocin1

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Abstract
A bio-assay has been developed for the quantitative determination of oxytocin. The assay makes use of the milk ejection phenomenon of rat mammary gland tissue in vitro. The time between the exposure of the mammary gland tissue to the oxytocin solution and the initiation of milk ejection (TT) was used as the quantitative parameter. The TT was determined by placing 2 mm3 pieces of mammary tissue containing milk into drops of solutions of known oxytocin concentration. Solutions of oxytocin containing from 1 x 10-2 through 1 x 10-10 IU/ml were quantified. Since a volume of 0.01 ml was used per determination, the actual amounts of oxytocin were 1 x 10-4 to 1 x 10-12 IU. The relationship between the logarithm of an exponential series of oxytocin concentrations and the logarithm of TT was found to be inverse and linear over the entire quantitative dose range. The simple materials and equipment, the small amount of time, the high sensitivity and the wide range of the linear dose-response relationship makes this a practical method for determining the amounts of oxytocin over a wide range of concentration.

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