Mesenterial-window hyperplasia in the lactating rat.

By examining the true mesentery adjacent to the small gut before and after weaning, as well as in age-matched controls, we found that the number of mesenteric windows, their total area, and their total DNA content increased significantly during lactation. Simultaneously, Feulgen-DNA absorption analysis in individual mesenteric cells showed that these had a normal DNA stemline, and a normal distribution within the G1-G2 range. The hyperplasia and growth developed and declined temporally somewhat parallel in the mesenterial windows and their adjacent small gut, suggesting that an as yet unknown common factor(s) governs the hyperplastic growth in both these tissues. The novel physiological, mesenterial-window hyperplasia in the lactating rat described in the present study may prove useful for studies of the mesenteric function and the regulation of cell proliferation.