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

The effects of epidermal growth factor (EGF) and cell density on the appearance of beta-adrenergic responses were examined in primary cultures of adult rat hepatocytes. The beta-adrenergic response was measured as the ability to accumulate cAMP by beta 2-agonist metaproterenol in monolayers that had been cultured without or with 20 ng/ml EGF. Hepatocytes cultured with EGF at a high cell density (1.0 x 10(5) cells/cm2) showed a relatively lower response to 10 microM metaproterenol. In contrast, when cultured at a low cell density (3.3 x 10(4) cells/cm2) with EGF, the cells showed a higher response to the beta-adrenergic agonist. These responses were blocked by the beta-adrenergic antagonist propranolol (10 microM). The beta-adrenergic response increased rapidly with culture time. The addition of cycloheximide (5 microM) to the culture abolished the expression of beta-adrenergic response. The enhanced beta-adrenergic response by 20 ng/ml EGF was partially inhibited by the addition of cytochalasin B (20 microM) to the culture. The cAMP-producing response to metaproterenol (10 microM) was dose-dependently inhibited by the specific x2-agonist UK-14304. Pretreatment of the hepatocytes with pertussis toxin (100 ng/ml) potentiated the beta-adrenergic response. These results demonstrate that augmented beta-adrenergic responsiveness can be acquired by adult rat hepatocytes cultured with 20 ng/ml EGF at a low cell density, and the beta-adrenergic response involves de novo synthesis of protein(s). The results also show that significant alpha 2- and beta-adrenergic responses coexist in the primary cultures of adult rat hepatocytes.