Circadian ultrastructural changes in rat gastric parietal cells

The ultrastructure of rat parietal cells of the gastric mucosa was investigated during the twenty-four hours of a day. Male rats were housed at ad libitum feeding under normal light conditions with dark night. The animals were sacrificed at 6.00 h, 12.00 h, 18.00 h and 24.00 h respectively, in groups of 5 animals after standard 24 hours of starvation.

From this material the electronograms of 356 parietal cells (19% in 6.00 h, 26% in 12.00 h, 21% in 18.00 h and 34% in 24.00 h samples) were evaluated. Based on literary data, the parietal cells were specified as secreting parietal cells (S, 38% of the total), secreting parietal cells returning to resting state (SR, 18% of the total), resting parietal cells (R, 35% of the total) and resting parietal cells tending to early secreting state (RS, 9% of the total).

Some types of parietal cells are statistically highly significantly (χ² = 130.9, p ⪡ 0.001) unequally distributed during the circadian rhythm: S are less numerous at 6.00 h (2% of the total) and 12.00 h (4% of the total) than expected (7 and 10% respectively), and more numerous at 18.00 h (11% of the total) and 24.00 h (21% of the total) than expected (8 and 13% respectively). Conversely, R are more numerous in the morning (13 and 15% instead of 7 and 9% respectively) and less in evening samples (4 and 3% instead of 7 and 12% respectively).

Distribution differences were proved statistically (χ²-test) for all cell-cell and hour-hour combinations except the combinations S-RS and 6.00 h to 12.00 h. The maximal differences in distribution were found to be between the amounts of 8 and R at 6.00 h and 24.00 h (χ² = 77.3, P ⪡ 0.001) and at 12.00 h and 24.00 h (χ² = 69.3, p ⪡ 0.001).

Thus, a distinct circadian rhythm of parietal cells, especially as to their fine cell structures involved in acid production was demonstrated. The results render further evidence of the rhythmicity of gastric acid production in rats.