Action of Synthetic Oxytocin on the Crop Gland of the Pigeon

Abstract

Cowie and Folley¹ have suggested that oxytocin released in response to the stimulation of suckling in rats may cause the release of prolactin. If oxytocin causes a release of prolactin in birds, then administered oxytocin should perhaps cause an increase in the crop gland weight in the pigeon, which is shown to respond to prolactin². This has been investigated by measuring the weight of the crop gland in pigeons (200–300 gm. in body-weight) after administration of 400 m.units of oxytocin (‘Syntocinon’, Sandoz Products Ltd.) systemically (200 m.units intravenously and 200 m.units intra-muscularly) and also intra-dermally (one unit) over the site of the gland for four days. The animals were killed on the fifth day when the crop glands were dissected out and weighed. The results are depicted in Fig. 1 as the mean of the percentage of the body-weights of the animals. Synthetic oxytocin in the doses used caused an increase in the crop gland weight of the pigeon, which differed significantly (P < 0.001) from the crop gland weights of the control pigeons. The pigeons injected with oxytocin after it had been incubated with sodium thioglycollate to inactivate its oxytocic activity³ did not show an increase of crop gland weight. The fact that oxytocin also has this crop-stimulating action on the pigeon makes results of blood and urine prolactin contents assayed by this method less acceptable as regards the specificity of the substance being measured. While the results are suggestive that oxytocin may, in birds, cause a release of prolactin, a direct action of oxytocin on the crop gland of the pigeon, not described before, has not been ruled out. Experiments are in progress investigating the mechanism of action of oxytocin on the pigeon crop gland and its significance.