Alkaline phosphatase isoenzymes in serum of rats during cholestasis

Alkaline phosphatase isoenzymes (API) in serum of rats during cholestasis are investigated. For comparison different membrane systems in liver are damaged. Proliferation of bile canaliculi, sinusoidal area, and endoplasmic reticulum, respectively, is induced by different toxic conditions. It is found that in cholestasis an API5 in serum arises which is not present in serum of normal rats, but can be detected in normal rat liver. Thus, it is not a de novo synthesis of this API. Under the condition connected with a proliferation of bile canaliculi we find this API5 in serum. Under different conditions without proliferation of bile canaliculi we do not find an increase of this API5. We assume, therefore, that API5 in cholestasis is produced by cells of the bile canaliculi rather than by liver parenchymal cells in the sinusoidal area. No difference is found in intra- or extrahepatic cholestasis.