Localization of liver fatty acid-binding protein and its mRNA in the liver and jejunum of rats: an immunohistochemical and in situ hybridization study.

The localization of liver fatty acid-binding protein (L-FABP) and its mRNA in the liver and jejunum was examined in normal and 3-day-fasted rats by means of immunohistochemistry using a specific antibody to L-FABP and in situ hybridization using a synthetic oligonucleotide complementary to L-FABP mRNA as probe. In the liver from normally fed rats, the signal for L-FABP mRNA in hepatocytes was distributed throughout the lobule, with higher intensity in the periportal than in the centrolobular region. After a 3-d fasting, the mRNA signal declined in intensity throughout the lobule, in accordance with the result of Northern blot analysis. Immunohistochemistry for L-FABP showed intralobular patterns of immunoreactivity similar to those of the mRNA signal in both fed and fasted animals. In the jejunum from fed rats, L-FABP-mRNA signal was abundant in the absorptive epithelial cells lining the lower two-thirds of villus and less abundant in the villus tip cells, while the intensity of L-FABP immunoreactivity remained high in the latter cells. Fasting brought about a downward shift of the mRNA signal to an area including the upper half of the crypt and the lower portions of villus, with decreased intensity in the rest of the villus. Immunohistochemistry also showed a downward extension of the immunoreactivity into the upper crypt area. The present results suggest that in situ hybridization is a useful tool to analyze regulations of the expression of L-FABP gene in the digestive organs in association with epithelial cell migration and dietary condition.