Mitsutoshi Kimura and Masahiko Ogihara (*)
Biochemical Pharmacology Group, Faculty of Pharmaceutical Sciences, Josai
University, 1-1, Keyakidai, Sakado, Saitama 350-02, Japan
(*) To whom correspondence should be addressed.
Abstract: We investigated whether or not proliferation of adult
rat hepatocytes induced by platelet-derived growth factor (PDGF) is affected
by alpha1-adrenoceptor agonists such as phenylephrine during
the early and late phases of primary culture. Adult rat hepatocytes underwent
significant DNA synthesis after culture with 10 ng/ml of PDGF for 2 hr at
a low cell density (3.3 x 104 cells/cm2). Under these
culture conditions, the number of nuclei increased significantly during
the 3.5-hr culture period. Hepatocyte DNA synthesis and proliferation induced
by 10 ng/ml of PDGF decreased slightly as a result of increasing the initial
plating density. An alpha1-adrenoceptor agonist, phenylephrine
(10-6 and 10-5 M), alone did not affect hepatocyte
DNA synthesis and proliferation, but markedly potentiated PDGF-induced hepatocyte
DNA synthesis and proliferation. The phenylephrine effect was mimicked by
phorbol myristate acetate (10-7 M), but not by ionomycin (10-5
M). The mitogenic effects of PDGF were almost completely blocked by treating
hepatocytes with genistein (5 x 10-6 M), U-73122 (3 x 10-6
M), sphingosine (10-5 M), wortmannin (10-7 M) and
rapamycin (10 ng/ml). These results demonstrate that PDGF can induce the
proliferation of adult rat hepatocytes rapidly in primary culture, regardless
of the initial plating density. The present results also suggest that following
stimulation with PDGF, activation of tyrosine kinase, phospholipase C, phosphatidylinositol
3-kinase, protein kinase C (PKC) and p70 ribosomal protein S6 kinase is
essential for the proliferation of adult rat hepatocytes. The co-mitogenic
effects of phenylephrine may involve PKC activation.
Keywords: Platelet-derived growth factor, Hepatocyte DNA synthesis, Hepatocyte
proliferation, alpha1-Adrenoceptor agonist, Phorbol ester