Both quantitative and histochemical studies of alkaline phosphatase, thymidine kinase (a marker for DNA synthesis and hence crypt cell activity), lactase, maltase, sucrase and sodium/potassium ATPase were undertaken. Three points emerged from these gut enzyme studies. First, while the levels of lactase fell, the residual level of lactase was demonstrably sufficient to handle most of the lactose load delivered from the stomach to the small intestine at 72 h after infection, the peak of clinical diarrhea. A corollary to this is that a child who becomes lactose intolerant must be suffering from severe erosion of intestinal villi over a significant length of the small bowel. Second, thymidine kinase levels peaked at 72 h after infection, at which point cell division in the villus base region was increased (Figure 7). Villus reconstruction also took place rapidly between 48 and 72 h after infection. Third, based on the accelerated appearance of sucrase in the reconstructed gut, it is unlikely that prolongation of diarrhea was due to the presence of ‘immature’ absorptive cells; an alternative explanation for prolonged secretion can be given in terms of altered villus microcirculation (see below). Confirmation of the secretory state of the gut was obtained by in vitro studies, which showed that the gut was maximally secretory 72 h after infection.
Remarkable changes occurred in the microcirculation of rotavirus-infected mouse intestine. Between 18 and 48 h after infection, villi became ischemic and atrophied throughout all areas of the small intestine. By 72 h after infection, villi had recovered their normal height and showed incipient hyperemic microcirculation. At 96 h after infection, hyperemic microcirculation was most marked. buy flovent inhaler
Between 120 and 144 h after infection, a second phase of villus atrophy occurred, which was more attenuated and confined to the upper and middle regions of the intestine. This phase was not accompanied by a widespread ischemia of villi; a minority of villi were short and ischemic but many appeared hyperemic. Recovery of villus microcirculation occurred at 168 h after infection, which coincided with the reappearance of crenated erythrocytes and recovery from diarrhea.
Intracellular concentrations of elements were measured by x-ray microanalysis in gut epithelia of infected mice. Although infection was limited to villus tip regions in the small intestine, significant changes in concentrations of sodium and chloride ions were observed (Figure 8), in both villus tip cells and villus base cells corresponding to the electron lucent cells in Figure 7.
Figure 7) Transmission electron micrograph of neonatal mice 72 h after infection with mouse rotavirus. Low power transmission electron micrograph showing longitudinal sections of several villi from small intestine of mouse 72 h after infection with mouse rotavirus. Most ente-rocytes in the upper regions of villi are electron opaque, vacuolated and obviously damaged. Cells at the villus bases are electron lucent and represent areas of cell replication; mitotic profiles were visible (small double arrows). Note the congested tip capillary (single arrow) and the patent subepithelial vessel (curly arrow). Reproduced with permission from reference 57. Scale bar = 25
Figure 8 ) X-ray microanalysis of neonatal mouse gut before and during infection with mouse rotavirus; sodium and chloride ion profiles. The analyses were performed in regions corresponding to the tips of villi (top), the translucent band of villus base cells (bottom) and crypt regions (Figure 7). No significant changes were observed in crypt regions (not shown). Striking changes were observed in villus bases of infected mice, in particular at 48 to 72 h after infection, concomitant rises in both sodium and chloride ions were observed. In contrast, in villus tips, sodium levels rose while chloride levels dropped at 48 h after infection. The arrow heads in the villus base panels indicate data from a dividing cell in control tissue. EDIM Epizootic diarrhea of infant mice.