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  • Author: K. S. RAGHAVAN x
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Although various hypotheses have been suggested to explain the mechanism of the antifertility effect of an intrauterine device (IUD), this mechanism is not known. It has been suggested that studies on the effect of an IUD on the blood level of oxytocin be carried out (W.H.O. Tech. Report No. 397).

In this investigation the circulating level of oxytocin in the plasma of rats with and without bilateral IUD's has been estimated both at oestrus and dioestrus. The IUD, a silk thread suture, was inserted as described by Chaudhury & Tarak (1965). The method of extraction of oxytocin from rat plasma was that of Folley & Knaggs (1965).

Female albino rats weighing 175–225 g. were used. Blood was collected from decapitated animals into chilled polythene beakers containing 500 i.u. heparin. Blood from three to eight animals was pooled. Plasma was obtained by centrifugation at 4° at 3000 rev./min. for 20 min.

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The evaluation of a radioimmunoassay of oxytocin is described. The method involved careful collection and transportation of blood at 4 °C, acidification of the plasma, extraction with Fuller's earth and radioimmunoassay using antisera raised in rabbits immunized against oxytocin conjugated to bovine serum albumin and 125I-labelled oxytocin. The antisera showed insignificant cross-reaction with a variety of small peptides including vasopressin and vasotocin. The limit of detection of the assay was 2·5 pg with intra-assay and interassay coefficients of variation of 7–15% and 12–18% respectively. Seventy-seven per cent (88 out of 116) of the pregnant women tested had detectable maternal plasma oxytocin. Serial samples of maternal plasma showed a significant increase in oxytocin from the first to the second stage of labour and a significant decrease in the third stage. Oxytocin concentrations in the umbilical arterial plasma were significantly higher in patients in labour. The significance of these findings is discussed.