Significance of liver canalicular changes after experimental bile duct ligation.

An ultrastructural morphologic, histochemical, and morphometric study was made on the canalicular structures in rat liver after experimental bile duct ligation (BDL). Four different canalicular structures are distinguished, which are proved by morphometry to correspond to the different types observed during perinatal maturation.Canaliculus type 4, corresponding to the excretory pole of a normal adult hepatocyte, is characterized by a lumen filled with regular, slender microvilli. Canaliculus type 3, corresponding to the canalicular structure described in cholestasis, has a wide lumen devoid of microvilli and is found 2–3 days after BDL. A transitional canalicular structure between type 3 and 4, partly provided with microvilli, is found from the first day after BDL. After 3 days of BDL an increasing number of other canalicular types is observed.Canaliculi type 2, showing an irregular lumen with irregular microvillus-like projections, and canaliculi type 1, representing intracytoplasmic invaginations of two adjacent cell membranes, are found together with canaliculi type 3 and type 3–4.After incubation for alkaline phosphatase, the enzyme activity is detected in canaliculi type 1, 3–4, and type 4.The striking analogy of the sequential changes in canalicular structures after BDL and during perinatal maturation leads to the following interpretation: (1) Canaliculi type 1 and 2, more frequently observed in longstanding cholestasis correspond to newly formed excretory poles of the hepatocytes. (2) Canaliculus type 3, or the so-called cholestatic canalicular type, reflects an inactive secretory function. Morphometrically this canalicular type shows a very low S/V relation which may be partly responsible for this secretory inactivity. (3) Canaliculus type 3–4 reflects a disturbed secretory function after BDL and a beginning secretory activity during perinatal maturation.