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Hormonal Regulation and the Effects of Glucose on Tyrosine Aminotransferase Activity in Adult Rat Hepatocytes Cultured on Floating Collagen Membranes¹

Departments of Oncology [G. M., G. L. S., H. C. P.] and Pathology [G. M., H. C. P.], McArdle Laboratory for Cancer Research, University of Wisconsin, Medison, Wisconsin 53706

Adult rat parenchymal hepatocytes can be maintalned. In primary culture on floating collagen membranes for prolonged periods of time. In this system the enzyme tyrosine aminotransferase is induced by glucoagon, (10^-6 to 10^-8 M) hydrocortisone (10^-5 to 10^-8 M), and cyclic adenosine 3':5'-monophorphate (cAMP) (10^-4 to 10^-5 M). Epinephrine (10^-4 M) induces the enzyme only in the presence of hydrocortisone. Addition of actinomycin D inhibited the induction of tyrosine aminotransferase by hydrocortisone and cAMP. Maintenance of the cultured hepatocytes in the presence of glucose (3 g/liter) results in partial suppression of the inducing effects of glucagon and cAMP. Cyclic guanosine 3':5'-monophosphate does not mimic the effects of glucose. These results demonstrate that the phenomenon of glucose repression of enzyme induction, demonstrated in vivo in mammallan liver, is independent of changes in levels of serum hormones, which occur in vivo as a result of glucose administration. This study also demonstrates that glucose repression is not mediated by changes in intracellular levels of cAMP and cyclic guanosine 3':5'-monophosphate.

¹ This study was supported in part by Grant CA-02575 from the National Cancer Institute.

² Postdoctoral trainee in biochemical pathiology of the National Institute of General Medical Sciences (GM-00130). Present address: Department of Pathology, Duke University School of medicine, Durham, N. C.

³ To whom requests for reprints should be addressed.

Received 11/10/77. Accepted 3/ 2/78.