血漿Oxytocin含量のRadioimmunoassay

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A simple radioimmunoassay was applied to the measurement of oxytocin in human plasma.<BR>Ten mg of synthetic oxytocin and 10 mg of porcine gamma globulin were dissolved in 4 ml of distilled water, and then added 150 mg of carbodiimide, after adjusted pH to 6-7. The solution was incubated 25°C for 4 hours and dialyzed overnight at 4°C against distilled water. An antibody to oxytocin was produced by intramuscular administration of the conjugate of oxytocin and globulin, emulsified with an equal volume of Freund's complete adjuvant, to rabbits at 2 weeks intervals. Oxytocin was radioiodinated by chloramine-T method, and then purified by gel filtration using Sephadex G-25. Plasma oxytocin was adsorbed by Florisil and extracted with acetone containing 1% acetic acid. Radioimmunoassay of oxytocin was performed by adding 0.1 ml of 125I-oxytocin and 0.1 ml of antisera to plasma extracts diluted with 0.05 M phosphate buffer containing 0.1% lysozyme (pH 7.4). After incubation at 4°C for 72 hours, antibody-bound antigen was separated using dextran-coated charcoal.<BR>A high specificity of immunoassay was demonstrated by the fact that large excess of angiotensin I and II, and ACTH did not displace labelled oxytocin from the antibody. Lysine-8-vasopressin and arginine-8-vasopressin showed very little cross-reaction in the assay, possessing only 0.002% of the immunological potency of oxytocin. The specific activity of 125 I-oxytocin was 166 μCi/μg. Adsorption and extraction capacities of Florisil were 96.6±2.1% and 85.7±2.5%, respectively. Intra-and inter-assay variability were 7.2±4.9% and 4.3±2.2%, respectively. The sensitivity of the assay was below 1pg/tube.<BR>Normal levels of plasma oxytocin were 0-2.2 pg/ml (n=13) in males and 0-10.4 pg/ml (n=10) in females. Plasma oxytocin levels in the 39th and 40th weeks of pregnancy were 27.9±4.14 pg/ml (n=4) and 29.8±17.1 pg/ml (n=13), respectively. The levels in creased to 33.1±12.1 pg/ml (n=7) and 37.1±17.5 pg/ml (n=7) in the first and third stages of labor, and decreased to 13.6±5.25 pg/ml (n=6) on the 2nd to 8th day after labor.<BR>The radioimmunoassay for oxytocin in plasma is considered to be sufficiently applicable for clinical use.
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血漿Oxytocin含量のRadioimmunoassay

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