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Summary. The concentrations of T-cell suppressor factor (TsF) were examined by competitive binding assays in the uterus, spleen, and regional lymph nodes draining the uterus in Day-5 pregnant mice or in ovariectomized mice given hormone treatments to induce conditions of delayed implantation or implantation. The amounts of immunoreactive TsF on Day 5 of pregnancy were 2·055 ± 0·302, 0·803 ± 0·088, 0·426 ± 0·136 ng TsF/mg extractable protein for the regional lymph nodes, spleen and uterus, respectively, during Day 5 of pregnancy. When implantation was prevented by ovariectomy on Day 4 followed by treatment with only progesterone, amounts of TsF (as a % of Day 5 value) were decreased to 57% in the uterus and increased to 141% in the spleen and 180% in the regional lymph nodes. When implantation was then initiated with the addition of oestradiol-17β to the progesterone treatment, amounts of TsF were increased to 206% in the uterus, 318% in the spleen, and remained unchanged at 180% in the regional lymph nodes. These experiments suggest that the amounts of TsF in the uterus and spleen are dependent upon the implantation process, whereas amounts of TsF in the regional lymph nodes are independent of this event.

Keywords: T-cell suppressor factor; implantation; monoclonal antibody; pregnancy; delayed implantation; mouse

Summary. Mouse embryos collected before implantation were incubated in vitro for 24 h with fluid rinsed from the uteri of ovariectomized female mice injected with progesterone, oestradiol-17β + progesterone, or oestradiol-17β alone. Although none of the zonae was completely dissolved, those incubated in fluid from animals treated with oestradiol + progesterone were subsequently more soluble in sodium thiocyanate (NaSCN) than those incubated similarly in control buffer, indicating a sublytic change during the incubation with uterine washings. Zonae incubated in fluid from animals injected with either hormone alone did not undergo such a change.

Summary. A monoclonal antibody, mAb 14-30, which binds T-cell produced suppressor factors (TsF) was used to study the possibility that molecules produced by suppressor T-cells play a role in maintaining pregnancy, presumably by protecting the fetus from the maternal immune system. Female mice were injected with mAb 14-30 at various times after mating. Overall, only 14% of the expected 68% of the mated and treated females were pregnant at term. In addition, Western blots were used to demonstrate the presence of TsF in fetuses, placentae, uteri and spleen of pregnant animals and its presence only in the spleen of non-pregnant animals. These experiments help to confirm results that indicate the importance of immune suppressor factors in maintaining pregnancy and extend these previous observations to include suppressor T-cell molecules.

Keywords: pregnancy; immunosuppression; mouse; T-cell; abortion

Summary. A variation of the dye dilution technique was used to determine the volume of uterine fluid in 'implanting' and 'delayed implanting' mice. The method involves rinsing Krebs—Ringer—bicarbonate buffer containing [methyl-¹⁴C]methylated-BSA through the uterine lumen and using the resulting decrease in concentration of the BSA to calculate the volume of uterine fluid. The results indicated that the volume of uterine fluid was essentially the same in 'implanting' and 'delayed implanting' mice (i.e. 300–400 nl/pair of uterine horns). The total amounts of a substance recovered by rinsing the uteri would therefore provide an estimate of relative concentrations in situ.

Summary. Preimplantation mouse embryos with intact zonae pellucidae were transferred into the uteri of ovariectomized females treated with progesterone, oestradiol-17β plus progesterone, or oestradiol-17β alone; the disappearance of zonae from the uterine lumen was used to determine the presence of 'zona-lytic' activity in situ. Lysis of zonae did not occur in animals treated with progesterone or oestradiol-17β alone. However, lysis did occur when oestradiol-17 β was combined with progesterone; 'zona-lytic' activity reached peak levels within 12 to 24 h, then decreased. Attachment of embryos to the uterine epithelium occurred only in animals treated with oestradiol-17β plus progesterone and was initiated at about the time of peak 'zona-lytic' activity. It is suggested that the chymotrypsin-like enzyme activity present in uterine fluid is involved with the initiation of implantation.

Summary. Rabbit blastocysts were homogenized by sonication, and centrifuged at 105 000 g for 60 min. The pellet was resuspended and incubated in phosphate buffer containing [1β-³H]testosterone and a NADPH generating system. The amount of ³H₂O produced was determined by liquid scintillation counting. Enzyme activity was calculated, after subtracting blank values obtained with boiled embryos, and expressed as pg testosterone aromatized per embryo per hour. Aromatase activity was undetectable to low on Day 5 and increased on Day 6 of pregnancy. There was a 10-fold increase in activity in Day-6 embryos cultured for 24 h, with a further 6-fold increase in activity in Day-6 embryos cultured for 48 h. The enzyme had an apparent K _m of 0·77 μm and was completely inhibited by an aromatase inhibitor. The results clearly indicate that the rabbit blastocyst has an increasing capacity for aromatization of testosterone at about the time of implantation.