title: Oxytocin determination by radioimmunoassay. III. Improvement to subpicogram sensitivity and application to blood levels in cyclic cattle.
abstract: An improved RIA for measurement of oxytocin in blood is described by using an extraction method with SEP-PAK C18 cartridges, which allows also concentration of the sample, a new antiserum with a higher sensitivity to standard oxytocin and preparation of the standard curve in buffer. The lower limit of assay sensitivity was 0.25 pg/tube, corresponding to 0.25-1.0 pg/ml plasma depending on the amount of plasma extracted. Hence, it was no problem to measure oxytocin basal concentrations in peripheral blood in the range of 0.6-4 pg/ml plasma depending on the stage of the oestrous cycle. The highest oxytocin concentrations occurred during the early and mid-luteal phase. The method has been applied also for samples from women, sheep, pigs and horses. Mean (+/- SD) recovery of oxytocin added to plasma or only buffer after extraction was 71.3 +/- 8.1%, and the coefficient of variation (CV) = 11.4% (n = 27 assays). The intra-assay CV of two control samples was 7.9 +/- 2.8 and 7.8 +/- 2.4% (n = 17 assays). The inter-assay CV of 5 control samples with low and high oxytocin concentrations varied between 10.8 +/- 17.3% (n = 25 assays). The 50% intercept was 2.5 +/- 0.3 pg, CV = 11.3% (n = 29 assays).
mesh_terms: D000818:Animals; D002417:Cattle; D004971:Estrus; D005260:Female; D010121:Oxytocin / Q000097:blood*; D011247:Pregnancy; D011863:Radioimmunoassay / Q000379:methods*
chemical_list: D010121:Oxytocin