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Cell Proliferation and Subcellular Localization of Alkaline Phosphatase Activity in Rat Liver Parenchyma during Azo Dye Carcinogenesis¹

Institut du Cancer de Montréal, Centre Hospitalier Notre-Dame, and Département d'Anatomie, Université de Montréal, Montréal, Canada

A combined method of phosphatase histochemistry and [³H]thymidine radioautography was devised to study the subcellular localization of alkaline phosphatase (AP) activity with the changing pattern of cell proliferation in precancerous livers of rats fed dimethylaminoazobenzene. After 50 hr of continuous infusion of [³H]thymidine into the rats, labeled liver tissues were fixed in glutaraldehyde. Sections were incubated for AP activity in a lead citrate medium (pH 9.4) with ß-glycerophosphate as substrate. Light and electron microscopic examinations of radioautographs revealed that focal groups of ³H-labeled hepatocytes within hyperplastic nodules were coincident to hyperbasophilic foci and distinguishable from the surrounding parenchyma, which was sparsely labeled. Proliferative hepatocytes in the foci exhibited enzyme reaction product indicative of AP activity along the entire surface membranes. The surface AP topography was in contrast to that of the surrounding hyperplastic parenchyma, in which regenerative hepatocytes showed a normal localization of AP activity at the bile canalicular membranes. The L-phenylalanine-sensitive and heat-resistant activity of hyperbasophilic hepatocytes was different from that of normal hepatocytes. The surface enzyme differentiation was accompanied by a decrease of cytoplasmic AP. Golgi elements apparently function in the mobilization of AP into the surface membranes. The phenomena of AP alterations might be related to the abnormal control of cell proliferation and cytodifferentiation leading to malignant growth.

¹ This work was supported by grants from the National Cancer Institute of Canada, le Ministère des Affaires Sociales du Québec, La Fondation J. H. Biermans, and Les Fondations J. Rhéaume.

² Research Associate of the National Cancer Institute of Canada.

Received 9/18/74. Accepted 11/ 8/74.

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