Effects of prostaglandin F
2α (PGF
2α) on the contractile activity of the oviductal isthmus, uterus and cervix in rabbits before and after mating were investigated by recording changes of their intraluminal pressures. PGF
2α(2 or 5mg/kg of body weight) was subcutaneously administered to rabbits prior to mating and then at 24 or 48 hours after mating. Effects of readministration of PGF
2α 1 or 2 hours later were also studied in estrous rabbits. PGF
2α effected an increase in the muscular activity of all organs examined. The responsive pattern was characterized by a spasmodic contraction, and in the uterus and cervix there was another pattern showing an increase in the amplitude and frequency but no change in tone. Readministration of 2mg/kg of PGF
2α 1 hour later caused a strong contraction as occurred earlier only in the uterus, while the second PGF
2α injected 2 hours later brought about stimulatory effects on the motility of each organ similar to those after the first PGF
2α injection. Readministration of 5mg/kg of PGF
2α 1 or 2 hours later evoked little or a slight stimulatory effect of the contractions of each organ, respectively. Administration of PGF
2α 24 hours after mating caused strong contractions in each organ, similarly at estrus. The effectiveness of PGF
2α in stimulating the motility of each organ was less remarkable when injected 48 hours after mating. It was concluded that the effectiveness of multiple injections of PGF
2α varies with dose and interval, and that the sensitivity of the reproductive organs to this drug decreases by at least 48 hours after mating.
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