Changes in liver lobule glycogen zonation during prolonged fasting of rats previously fed a 30% casein diet and adapted to a controlled feeding schedule.

Changes in the lobular distribution of liver glycogen were studied during the prolonged fasting of young adult male Sprague-Dawley rats that were previously adapted to a 30% casein diet and to the 2 + 22 controlled feeding and lighting schedule. The optical density of glycogen, revealed in fixed liver cryostat sections by the periodic acid-Schiff procedure, was determined in the periportal (P), midlobular (M), and centrilobular (C) regions of the liver lobule at various times during a 196-hour fasting period. The prolonged fast could be divided into 3 phases with respect to liver glycogen variation: initial glycogen depletion, glycogen resurgence, and final glycogen depletion. Glycogen was lost from all regions of the liver lobule during the initial glycogen depletion phase. During the glycogen resurgence phase, a lobular glycogen concentration gradient formed (P greater than M greater than C). The simultaneous occurrence of increasing liver glycogen, increasing liver tyrosine aminotransferase activity, and decreasing body fat during glycogen resurgence suggests that the young adult rat does not spare body protein during starvation. During the final glycogen depletion phase, liver glycogen was again present in a lobular gradient (P greater than M greater than C) but the absolute amount of glycogen in each region of the lobule was markedly reduced in comparison with rats killed during glycogen resurgence.