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called transitional cells; albumin was present in both typical hepatocytes and some transitional cells. This work stresses the importance of careful selection of experimental conditions for immunolocalization studies on exportable liver proteins. Our data indicate that at least part of the hepatocytes are functionally homogeneous in regard of AlP and albumin production, and that AFP follows the secretion scheme generally recognized for liver export proteins. Albumin and a,-fetoprotein (AFP) are two plasma proteins with physicochemical, functional, and structural similarities, suggestive of a basic albumin-like biological function for AFP.

The two-step collagenase perfusion method originally developed for the high yield isolation of parenchymal cells from adult rat livers has been adapted to rats of 1 day, 1 week, and 2 weeks of age. The use of this method to isolate hepatocytes from five or six rats of the respective ages demonstrated its reliability in terms of cell yield, percentage of single cells, and cell viability. In all cases, hepatocytes attach with high efficiency to fibronectin precoated dishes using serum-free culture medium. The dynamics of spreading is faster for newborn hepatocytes than adult ones. The functional integrity of these parenchymal liver cells was assessed by their capacity to secrete albumin and alpha-fetoprotein in serum-free medium and to express lactate dehydrogenase activity over a 24-hr period in primary culture.

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