Suckling-induced release of cholecystokinin into plasma in the lactating rat: effects of abdominal vagotomy and lesions of central pathways concerned with milk ejection.

Plasma levels of cholecystokinin were increased in response to suckling in lactating rats. Efferent electrical stimulation of the vagal nerve increased the concentration of cholecystokinin in plasma. Abdominal vagotomy was found to block the suckling-induced release of cholecystokinin. Furthermore, lesions to the lateral midbrain, which disrupt the oxytocin-mediated milk-ejection reflex, were shown to inhibit the increase in plasma cholecystokinin. These results show that the suckling-induced release of cholecystokinin into plasma in lactating rats is dependent upon the vagal nerves and the central neural structures concerned with milk let-down.