Nucleic acid and protein content of rat cecum mucosa in dietary adaptation-growth by cellular hyperplasia

Does dietary fibre stimulate intestinal epithelial cell proliferation in germ free rats?

The aim of the present experiment was to investigate the role of hind gut fermentation in the proliferative response of the intestinal epithelium to dietary fibre. We have previously shown that refeeding starved rats with an elemental diet supplemented with fermentable dietary fibre (but not inert bulk) is capable of stimulating intestinal epithelial cell proliferation throughout the gastrointestinal tract. Three groups of 10 germ free (GF) rats and three groups of 10 conventional (CV) rats, were used. All groups were starved for three days and then refed for two days with either an elemental diet (Flexical); Flexical plus 30% kaolin; or Flexical plus 30% of a fibre mixture. Cell production was determined by the accumulation of vincristine arrested metaphases in microdissected crypts. There was no significant difference between refeeding the rats with an elemental diet alone or with kaolin supplementation, however, the addition of fibre in CV rats was associated with a significant increase in intestinal crypt cell production rate in both the small intestine (p less than 0.01) and the colon (p less than 0.001). This marked proliferative effects of fibre was abolished in the GF rats. It can be concluded that it is the products of hind gut fermentation, not fibre per se that stimulate intestinal epithelial cell proliferation in the colon and small intestine.

Adaptation of electrolyte transport in rat large intestine after proximal resection. I. Cecum and colon after 60% jejunoilectomy

Electrolyte transport was studied in rat cecum and colon adapting to 60% resection of the small intestine. Four weeks after surgery, the absorbing gross surface area, dry and wet weight, net absorption in vivo of sodium, chloride and volume, net potassium secretion, transmural electrical potential difference and mucosal Na-K-ATPase specific activity were determined. In the cecum, all tissue mass parameters were increased compared to sham-operated controls. Net transport was stimulated per organ but not per unit mass, and potential difference and Na-K-ATPase remained unaffected. In the colon, surface area and wet weight increased slightly while dry weight and electrolyte transport were not influenced. Thus, by enlargement without a change in cell function, the cecum but not the colon contributes to electrolyte homoeostasis after 60% jejunoilectomy in the rat. Na-K-ATPase specific activity and electrical potential difference were higher in the colon than the cecum, suggesting segmental heterogeneity of the larger bowel with respect to Na-K-ATPase-linked active sodium absorption.

Decreased cyclic GMP levels in rat cecum mucosa during adaptive stimulation of Na-K-ATPase

In rat cecal mucosa, Na-K-ATPase specific activity and sodium and fluid absorption were increased by giving polyethylene glycol administration with the drinking water. Whereas cyclic AMP levels were unchanged, cyclic GMP was reduced by about 50%. This finding suggests a regulatory role of cyclic GMP in intestinal sodium and fluid absorption.

Induction of Na-K-ATPase in plasma membranes to rat cecum mucosa by diet: time course and kinetics

Dietary polyethylene glycol (PEG) induces an increase in the specific activity of Na+-K+-activated adenosine triphosphatase (Na-K-ATPase) in the cecum mucosa of rats. Using cecum mucosa homogenates and cellular subfractions obtained by differential centrifugation, the induction process was studied with respect to time course, subcellular distribution and properties of the enzyme. In comparison with controls, Na-K-ATPase specific activity was stimulated in PEG treated rats in the total homogenate and the microsomal (105000 X g) but not in the mitochondrial (9000 X g) or nuclear (1000 X g) sediment. The specific activity of Mg-ATPase did not change in any of the fractions. Na-K-ATPase induction was statistically significant after 2 days and complete after 1-2 weeks, in parallel with the previously described stimulation in net sodium absorption. Kinetic analysis showed Vmax for ATP to be doubled while Km for ATP, Na and K as well as the optimal Mg/ATP ratio and Ki for ouabain remained unchanged. It is proposed that Na-K-ATPase and active sodium transport are closely associated in rat cecum and that dietary Na-K-ATPase stimulation is due to the induction of more enzyme molecules per unit basolateral cell membrane.