Changes in plasma concentrations of arginine vasotocin after intrauterine injections of prostaglandin F-2 alpha and acetylcholine at various times during the oviposition cycle of the domestic hen (Gallus domesticus)

Prostaglandin F-2 alpha (PGF-2 alpha, 1 microgram) and acetylcholine (10 mg) were injected into the uterus of chickens 23, 21, 16, 8 or 4 h before expected oviposition. Plasma concentrations of immunoreactive arginine vasotocin and PGF were measured in relation to the time of administration of PGF-2 alpha or acetylcholine or to the premature oviposition that was induced. PGF-2 alpha or acetylcholine administration caused premature oviposition and a marked increase in plasma arginine vasotocin levels only when an egg was present in the uterus. Changes in plasma PGF concentrations were not observed. After premature oviposition was induced, plasma values of PGF and arginine vasotocin increased at the expected time of oviposition. Manual stimulation of the uterus 4 h after oviposition also stimulated arginine vasotocin release. During spontaneous oviposition, a rise in plasma PGF concentration preceded increases in uterine contractility and plasma arginine vasotocin concentration. These results suggest that PGF may stimulate uterine contractility which in turn causes the release of arginine vasotocin to provide an additional contractile stimulus during oviposition.