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A radioimmunoassay for oxytocin in cow plasma is described. Antisera were raised in rabbits against synthetic oxytocin coupled to bovine thyroglobulin. Iodinated oxytocin free of unlabelled oxytocin and most likely also free of diiodo-oxytocin was used as radioactive tracer. The tracer showed a high degree of purity, and was stable on storage. It could be used in the assay for 2–3 months. The assay showed very little crossreactivity with vasopressin. Acetone was used for the extraction of oxytocin from plasma as well as from standards made of synthetic oxytocin in pooled cow plasma. Inhibition curves obtained with plasma collected from cows at parturition were parallel to those obtained with the oxytocin standard preparation. The mean recovery of oxytocin added to cow plasma was 106 % (sd = 14). The within-assay coefficient of variation (CV) varied from 5.2 to 10.9 %, and the between-assay CV was in the order of 13 %. The assay sensitivity was 1 pg (0.5 μU) per tube, corresponding to 3 pg/ml plasma. Around the time of milking the plasma oxytocin profile showed a strong response to the preparation for milking, and a further effect releated to the attachment of the teat cups of the milking machine. Peak concentrations were in the range of 15–50 pg/ml. During parturition there was a peak of oxytocin (65 pg/ml) coinciding with the expulsion phase. After this peak levels decreased but remained measurably elevated until the expulsion of the placenta. The plasma disappearance curve for immunoreactive oxytocin after the infusion of 100 IU oxytocin over a period of 1 h showed two components with apparent half-lives of 7–9 and 25 min, respectively.

Growth and differentiation of the mammary gland during development and lactation are controlled by complex hormonal mechanisms. Additionally growth factors are supposed to act as local mediators of the hormonally controlled developmental processes. Mammary tissue for this study was obtained from non pregnant control heifers, primigravid heifers (second part of pregnancy), around parturition, during lactation (early and late) and from dry cows. Using RT-PCR and ribonuclease protections assay (RPA) the expression of the following growth factors was studied in the different phases bovine mammary gland development: Insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), fibroblast growth factor 1 (FGF-I), fibroblast growth factor 2 (FGF-2), transforming growth factor alpha (TGF-alpha). Additionally the expression of fibroblast growth factor receptor (FGFR) and growth hormone receptor (GHR) was investigated. The cellular distribution pattern of several of these growth factors and GHR was obtained using Immunocytochemical techniques. The detailed expression and localization pattern of these growth factors are presented and their role in the local regulation of the bovine mammary gland is briefly discussed.