ao et al. (1999) reported that human recombinet interferon gamma (hrIFN γ) exerted a certain anti contraceptive effect on the pregnant rabbit. In order to investigate the possible mechanisms by which interferon gamma (IFN γ) exerts its deleterious effect on pregnancy, 12 New Zealand breed rabbits were used as an animal model. One day (Day 1) after the females were mated with male animals, They were randomly divided into 3 groups. There were control, hrIFN γ 50 000 IU and hrIFN γ 100 000 IU groups. Saline and hrIFN γ of different doses were administered respectively to control and experimental rabbits via vaginal muscular injection on Day 6 and were killed on Day 12 of pregnancy. The fetus and placenta were weighed. The blood was collected before injection and at various intervals(6, 12, 24, 48 and 96 h) after injection. The concentration of serum progesterone were measured by radioimmunoassay. The apoptosis in placenta were examined by DNA fragmentation analysis. The results were as folloows: 1) In control, 50 000 IU and 100 000 IU hrIFN γ groups, progesterone level in serum were 26 20±0 74 ng/ml,17 81±0 55 ng/ml and 10 97±0 84 ng/ml respectively at 96 h after injection. In contrast with control group, progesterone production dropped significantly in rabbits treated with hrIFN γ, especially 100 000 IU hrIFN γ. 2) Apoptotic fragmentation of DNA(180 bp units) in placenta were detected both in control and experimental groups. The scan density of degraded DNA fragmentation in experimental group was higher than that in control, which suggested that apoptosis in placenta was further induced by hrIFN γ, especially by high dose hrIFN γ. In addition, the weight of placenta in rabbits treated with hrIFN γ reduced significantly as compared with that in control group( P <0 01). We suggest that hrIFN γ inhibits the secretion of progesterone, as a result of inducing apoptosis in placenta.
