Circadian morphometric variation in gastric parietal cell populations of the rat

Gastric parietal cells of rats maintained under standardized conditions and fed ad libitum were examined by electron microscopy at 6 time points of the 24-hr day. Morphometric determinations were made on 4 cell characteristics. The volume density of secretory canaliculi was maximal at the mid-dark sampling point and decreased during the light phase; a secondary peak was seen 1 h before the onset of darkness. The surface density of microvesicles and RER fluctuated inversely with the pattern displayed by secretory canaliculi. The number of multivesicular bodies per cytoplasmic area exhibited a single peak, 1 h after the onset of darkness. It was further noted that parietal cells in the necks and bases of glands differed morphologically and that their organelle populations varied at individual circadian rates.