Thesis (M.Sc.)--Chulalongkorn University, 1983

The effect of silk thread suture intrauterine device (IUD) on the binding characteristics and concentration of progesterone re-ceptor in rat uterus was investigated by using 3H-progesterone as specific binding ligand. The IUD showed no effect on the binding affinity of progesterone receptor. The dissociation constant (Kd) of cytosolic progesterone receptor (PRc) in the control and IUD horns were similar whether they were compared in the same stage or between stages of es-trous cycle. The mean Kd of Prc in the control horn was 0.59 +0.03 nmol/l and was 0.56 + 0.02 nmol/l in the IUD horn. Similarly, there was no significant difference in the Kd of nuclear progesterone receptor (Prn) between the control and IUD horns. The Kd value of PRn was 0.89 + 0.10 nmol/l in the control horn and was 0.89+0.06 nmol/l in the IUD horn. All these results indicated that IUD had no effect on binding affinity and sedimentation property of progesterone receptor. It significantly caused a decrease in progesterone receptor concentration of which the underlying mechanism is not yet available from present data. The reduction of progesterone receptor in the presence of an IUD however may alter the uterine sensitivity to progesterone which probably contribute to the contraceptive effect by causing failure of blastocyst implantation on Day 5.