Cell-density-dependent expression of the alpha(2)-adrenergic response by epidermal growth factor (EGF) in primary cultures of adult rat hepatocytes.

Effects of epidermal growth factor (EGF) on the expression of alpha(2)-adrenergic responses were examined in primary cultures of adult rat hepatocytes. The alpha(2)-responses were assessed by the inhibition of the rate of forskolin-stimulated cAMP formation by the selective alpha(2)-adrenergic agonists, oxymetazoline and UK-14304. Hepatocytes cultured with EGF (20 ng/ml) at a high cell density (1.0 x 10(5)/cm2) showed almost no response to the alpha(2)-adrenergic agonists, oxymetazoline and UK-14304 (1-100 mu M). In contrast, when cultured at a low cell density (3.3 x 10(4) cells/cm2) with EGF, forskolin-stimulated cAMP production was inhibited by oxymetazoline and UK-14304 in a dose-dependent manner. The alpha(2)-response was blocked by the alpha2-antagonist yohimbine (10 mu M). It was also reversed by treatment of hepatocytes with pertussis toxin (100 ng/ml). In addition, the effects of EGF on the appearance of alpha(2)-responses were almost completely inhibited by treatment of the hepatocytes with genistein (10 mu M) or cytochalasin B (10 mu M). The alpha(2)-response was abolished when cycloheximide (5 mu M) was added to the cultures. These results demonstrate that when cultured at a low cell density with EGF, adult rat hepatocytes acquire a significant alpha(2)-adrenergic response. The expression of this alpha(2)-response is associated with de novo protein synthesis.