Arginine vasotocin induces bearing down for oviposition in the hen.

An intravenous injection of arginine vasotocin (AVT) at 16 h before the expected oviposition of the initial egg of an egg-laying sequence caused bearing down for oviposition. Oviposition was increased up to 100% by increasing the dose of AVT up to 1 microg, but it decreased when the dose was 10 and 20 microg. Bearing down was observed even when the oviposition was not induced by the injection of a higher dose of AVT. The results of the present experiment suggest that bearing down is not necessarily caused by the entering of egg into the vagina, but instead may be caused by hormonal stimulus of AVT receptors present in vaginal tissue.