Coordinating mechanisms of prostaglandins and vasotocin in the control of ovulation-oviposition

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Uterine electromyographic activity (EMG),plasma concentrations of prostaglandin(PG) F and E, and arginine vasotocin(AVT) were simultaneously measured in relation to PGE_2-induced premature oviposition and to indomethacin-blocked oviposition in chickens. The administration of indomethacin (5 mg, im) 3 hr before the predicted time of oviposition delayed egg lay by 8-14 hr, whereas control hens laid eggs at the predicted time. In indomethacin-treated hens increases in uterine EMG activity and plasma concentrations of PGF,PGE,and AVT were not observed at the expected time of oviposition, whereas a marked increase in plasma PGF and AVT occurred during spontaneous oviposition . The intrauterine administration of PGE_2(1<micrn>g) 3 hr before predicted oviposition induced premature egg lay within 5 min. Premature oviposition was accompanied by significant elevations in both uterine EMG activity and plasma levels of AVT. Changes in plasma levels of PGF and PGE were not observed. When premature oviposition was induced, significant increases in EMG activity and plasma concentrations of PGF and AVT were observed at the expected time of oviposition in the absence of an egg in the uterus. The administration of PGE_2 at the predicted time of oviposition in hens pretreated with indomethacin induced oviposition which was accompanied by a significant increase in plasma AVT levels. The results suggest that AVT release is stimulated by uterine contractility in chickens.