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.