Oxytocin assay

A series of 1,3,4-triazoles has also been patented by Serono/Applied Research Systems [103]. The 2-benzylthio compound, (48), had a if of 45 nM in a human oxytocin-binding assay. 

Fig. 7. An experiment showing the efficiency of fractional precipitation by ammonium sulfate in assays for oxytocin (O—O, A—A), ACTH (0—0, A—A) or insulin (0—0, A—A). With oxytocin there is a substantial gap between the concentration of ammonium sulfate required to precipitate bound antigen and the concentration that will precipitate free antigen. By contrast, with insulin there is virtually no gap and the procedure would not be suitable for an assay. From Chard. ...

Numerous immunoassays for measuring oxytocin in plasma or urme have been described. However, their routine clinical application has been limited because of a lack of physiological relevance to human reproductive disorders and because of a lack of easy-to-use immunoassays with acceptable sensitivity and specificity. With most plasma assays, a preliminary extraction procedure with column chromatography is required, not only to concentrate the minute amount of hormone that is present in the specimen, but also to remove nonspecific interfering substances. 

The foremost advantage of the chemical assay is that the specificity of the analysis can be tested with the most rigid criteria. In the pituitary assay of oxytocin and vasopressin (Gruber et a/., 1976), specificity was demonstrated by the following four criteria (1) The oxytocin and vasopressin peaks were identified by their retention times. (2) Addition of synthetic oxytocin or vasopressin to the pituitary extract resulted in a quantitative increase in the height of the specific peak with no noticeable peak broadening. (3) After purification by reverse-phase chromatography, each of the nonapeptide fluorophors was collected, hydrolyzed in 6 N HCl, and then characterized... 

In a subsequent investigation by Heller and Zaimir (1949), oxytocin concentrations in the posterior lobe of the human pituitary gland were assayed on the same samples as those employed by the authors for determination of antidiuretic activities. The variation in the hormone level with age showed great similarity with that recorded for the antidiuretic hormone. The mean oxytocin content observed per milligram of dry tissue was 150 milliunits for newborn children (N = 15) and 754 milliunits for adults (N = 12). Values of 950 and 1050 milliunits were found for samples obtained from 2 adolescent children. The observed increase in the pituitary oxytocin potency during maturation is in agreement with. Tores and Zschim-mer s conclusions. 

An unexpected property shown by the hormonogens was their ability to inhibit the response to oxytocin in the milk-ejection and avian depressor assays but this property, too, can be explained by the gradual release of oxytocin - it can be closely. mimicked by infusing oxytocin at suitable rates (8). 

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