Abstract
Effects of prostaglandin F2α (PGF2α) and flufenamic acid (FA) on termination of pregnancy were investigated in Wistar strain rats after day 17 of pregnancy. Results obtained are as follows.
1. Main urinary metabolite of endogenous PGF2a (PGF2a-MUM) and serum progesterone (P) levels were successively measured. PGF2a-MUM levels (ng/total 24-hour urine) increased from 594.5 on day 18-19 of pregnancy to 1242.5 on day 19-20 and to 1515.8 on day 21-22. P levels (ng/m/) decreased from 37.5 on day 19 to 16.7 on day 20 and 10.7 on day 21. Parturition cccured in two cases out of ten on day 21, seven on day 22 and one on day 23.
2. When FA was subcutaneously administered every day from day 19 of pregnancy until partu-rition, the decrease of serum P level (ng/ml) was delayed compared with control, showing 33.1 on day 20 and 19.4 on day 21, and parturition was also evidently prolonged in four cases out of eleven occurring on day 22, five on day 23 and one on day 24.
3. When the total dose of 0.5-1.0 mg/kg of exogenous PGF2α were administered intramuscularly, induction of parturition was clearly recognized and this effect was observed 1-2 days after adminis-tration. Parturition-inducing effect of PGF2α was not inhibited with FA, but was inhibited with P.
4. The fall of P level and elevation of intra-uterine pressure were recognized with exogenous PGF2α. It required 48 hours to decrease to the extent of P level at near parturition, though the uterine contractile effect lasted only 40-60 minutes. Repeated administration of PGF2α, at the dose causing no uterine contraction, also induced parturition. These results suggest that the increase of endogenous PGF2α and the resultant luteolytic effect play important roles in spontaneous parturition in rats. It was considered that the luteolytic factor also largely accounts for the mechanism of parturition-inducing effect of exogenous PGF2α.
