Effects of oxytocin, vasopressin, and acetylcholine on glucose metabolism in mammary tissue in vitro.

The mammary gland of the rat undergoes profound metabolic changes after parturition. The rate of oxygen uptake, the respiratory quotient (l), and the activity of the phosphogluconic acid oxidative pathway increase markedly (2, 3). These alterations disappear within 1 or 2 days after the suckling young are weaned. The hormonal “environment” also changes at these times. After parturition, the source of placental hormones is lost, there is probably a release of prolactin from the pituitary (4), and there is a release of oxytocin in response to suckling (5). The hormonal changes after weaning are not as well documented, but there is certainly less reflex stimulation for the release of oxytocin. Consideration of the changes in oxytocin release which parallel the changes in mammary metabolism occasioned the investigation reported here, in which an effect of oxytocin, vasopressin, and acetylcholine on glucose oxidation has been demonstrated in rat mammary gland slices.