Effect of intrauterine injection of casein on fetal survival in rat: a new pharmacological approach for contraception

BackgroundThe incidental finding of casein as a possible new local pharmacological contraceptive prompted us to assess its validity in an experimental rat model.MethodsThe intrauterine injection of 150 μg of bovine α-casein dissolved in 150 μL phosphate-buffered saline (PBS) was performed on one uterine rat horn on days L5–L7, whereas the contralateral horn was used for injection of 150 μL PBS as a control. Intraperitoneal injection of α-casein (5 mg/mL, 2 mL/rat) was performed on day L5. The rats were killed by cervical dislocation on the day L14.ResultsThe effect of an α-casein on fetal resorption rate was assessed following the unilateral injection of 150 μL of α-casein (1 mg/mL in PBS) and compared with the effect obtained following the contralateral injection of 150 μL PBS. The unilateral injection of α-casein on day L5 caused a significant increase in fetal resorption rate as compared with the contralateral uterine horn injected with PBS (p<.00001). The decrease in α-casein concentration from 1 to 0.3 mg/mL caused a reduced, but still significant, effect on fetal resorption rate (p<.0001). The injection on days L6–L7 caused a local effect of resorption near the injection site. There was no effect on fetal resorption rate following the injection of α-casein intraperitoneally.ConclusionOur data suggest a new pharmacological approach for contraception, based on local intrauterine effect of α-casein in an experimental rat model. The exact mechanism of action related to casein should be further studied.