Parenteral nutrition, brain glycogen, and food intake

To determine whether brain glycogen concentrations change during parenteral nutrition, Fischer 344 rats with jugular vein catheters received 0.9 N saline or parenteral nutrition providing 100% of daily calories (PN-100). Rats were killed after 4 days of PN-100 and serially after PN-100 was stopped. Food intake decreased during PN-100 to approximately 15% of control, but total kilocalories eaten and infused over the 4-day PN-100 period was approximately 130% of control. Food intake of PN-100 rats remained low for 3-4 days post-PN-100. At the end of the 4-day PN-100 period, plasma glucose and insulin (P = 0.01) and whole brain glycogen (P < 0.005) were higher than but similar to control within 24 h of PN-100 being stopped. When PN-100 rats were not allowed to eat during the infusion period, plasma glucose was lower, plasma insulin higher, and brain glycogen content the same as in control rats after 4 days of PN-100. The increased brain glycogen was the likely consequence of the hyperglycemia and hyperinsulinemia during PN-100 and was not causally associated with the reduced food intake either during or immediately after PN-100.