Metabolic responses to suckling in postpartum lactating rats

The effects of suckling on the metabolic activity both of pituitary tissue and of subnuclei in the supraoptic and paraventricular nuclei of the hypothalamus were assessed by means of the [14C]deoxyglucose (2-DG) method of autoradiography. Three groups of female rats were deprived of their pups and of food for 6 h on the fifth or sixth day after parturition. Metabolic activity was assessed either before, during, or after a bout of suckling. The anterior pituitary is more active in suckled than in either non-suckled or postsuckled females. These differences may be a consequence of depletion/transformation/repletion of prolactin during a bout of suckling. The posterior pituitary is metabolically more active in suckled females and in postsuckled females than in non-suckled rats. These differences may reflect metabolic activity needed for the dynamics of oxytocin release and the restoration of ionic gradients. The dorsal and ventral subdivisions of the supraoptic nucleus and the lateral, dorsal, and posterior subnuclei of the paraventricular nucleus were more active in postsuckled females than in non-suckled females. These metabolic changes in the subnuclei of the magnocellular neurohypophysial system may reflect increased resynthesis of oxytocin (and vasopressin) in the cell bodies following a bout of suckling.