Enumeration of S-phase cells in normal rat liver by immunohistochemistry using bromodeoxyuridine-antibromodeoxyuridine system.

The visualization of incorporation sites of the thymidine analog bromodeoxyuridine (BrdU) into DNA, detected by immunocytochemistry, has been proposed as an index of the percentage of S-phase cells in a variety of tissues and as an easy, less expensive alternative to autoradiography. This technique has not yet been applied to the study of physiological cell renewal in the normal liver. In the present study, results obtained with this method in the liver of normal young adult rats is reported. BrdU was administered in vivo and subsequent incorporation was detected by the PAP technique using monoclonal anti-BrdU antibodies. The nuclei exhibiting a positive reaction within the liver were few and accounted for about 0.45\% of all hepatocytes. Positive cells were located preferentially in zone 1, which contained 82.7\% of the labeled cells. Zone 2 contained 15.4\%, while only 1.9\% of the labeled cells were found in zone 3. Positive-staining Kupffer cell nuclei were rare (about 0.5\% of all Kupffer cells) and were distributed randomly in the hepatic lobule. These findings provide quantitative data about hepatocyte renewal in the normal liver in the absence of a growth stimulus. The simplicity and the reproducibility of this technique suggests that further application of this method in situations assessing hepatic regeneration are indicated.