Effect of nordihydroguaiaretic acid on glucose absorption, metabolism and (Na(+)+K+)-ATPase activity in rat jejunum.

A regulatory role of endogenously synthesized eicosanoids on the absorption, transmural transport and metabolism of glucose in perfused, isolated loops of jejunum in vitro was investigated using the lipoxygenase/cyclooxygenase inhibitor, nordihydroguaiaretic acid (NDGA). NDGA diminished glucose absorption over the range 100-500 microM: maximal inhibition at 500 microM NDGA was 52 +/- 9 and 64 +/- 9% (mean +/- SE, P < 0.001) for jejuna from fed rats and rats maintained on glucose water for 48 hr, respectively. In each instance, transmural transport was effectively abolished. The vectorial disposition of lactate release was also changed such that the ratio of luminal to serosal production was increased from 0.19 +/- 0.02 to 1.72 +/- 0.12 (P < 0.001) in fed rats, indicating inhibition of the Na+ pump. NDGA inhibited (Na(+)+K+)-ATPase activity in whole mucosal homogenates with a concentration dependence similar to that observed for glucose absorption. However, NDGA also inhibited Mg(2+)-ATPase activity in whole homogenates and purified rabbit skeletal muscle phosphofructokinase under the same conditions. The results are discussed in terms of the dissipation of the transmembrane Na+ gradient via direct inhibition of the (Na(+)+K+)-ATPase by NDGA. Inhibition of the ATPase precludes the use of NDGA as a suitable drug with which to investigate the role of endogenously synthesized eicosanoids in the regulation of intestinal function.

The isolation and characterization of phosphofructokinase from the epithelial cells of rat small intestine.

1. Only a single phosphofructokinase isoenzyme is present in the mucosa of rat small intestine. 2. Mucosal phosphofructokinase was purified to yield a homogeneous preparation of specific activity 175 units/mg of protein. 3. The native enzyme is a tetramer, with monomer Mr 84 500 +/- 5000. 4. The native enzyme may be degraded by the action of endogenous proteinases to give two products with the same specific activity as the native enzyme: degradation occurs in the order native enzyme leads to proteolytic product 1 leads to proteolytic product 2. 5. Proteolytic product 1 has a greater mobility in cellulose acetate electrophoresis at pH8 and binds more strongly to DEAE-cellulose than does native enzyme; the converse is true for proteolytic product 2. 6. Proteolytic product 1 is a tetramer with a monomer Mr about 74 300; proteolytic product 2 is also a tetramer. 7. Native enzyme can only be prepared in the presence of proteinase inhibitors; partial purifications based on simple fractionation of crude mucosal extracts in the absence of proteinases inhibitors contain proteolytic product 2 as the main component and proteolytic product 1 together with little native enzyme. 8. Purified native mucosal phosphofructokinase displayed little co-operativity with respect to fructose 6-phosphate at pH 7.0 and was only weakly inhibited by ATP.