Induction of monooxygenase and UDP-glucuronosyltransferase activities in primary cultures of rat hepatocytes.

The inducibility of two monooxygenase and UDP-glucuronosyltransferase (GT) forms was studied in primary cultures of adult rat hepatocytes. The following enzyme activities were determined: cytochrome P-448-dependent ethoxyresorufin O-deethylase (ERDE) and cytochrome P-450-dependent aldrin epoxidase (AE), and, furthermore, the GT form(s) metabolizing 3-hydroxybenzo(a)pyrene (GT1) and the GT form(s) metabolizing 4-hydroxybiphenyl (GT2). The results were as follows. The activity of AE and GT2 decreased markedly during the first days of culture, whereas ERDE and GT1 remained stable or even increased slightly. The maintenance of ERDE activity was dependent on the presence of dexamethasone. Pregnenolone-16 alpha-carbonitrile (PCN), phenobarbital (PB), and benz(a)anthracene (BA) induced the activity of ERDE in hepatocytes cultured in HM 84 medium by a factor of 4, 8, and 12, respectively. Similar factors of induction were obtained at the fifth day of culture using a modified Leibovitz L-15 medium. However, the time course of induction differed greatly in the two media. BA and PB had an additive effect on ERDE activity, suggesting different mechanisms of action for the two inducers. Monoclonal antibodies directed against cytochrome P-448 inhibited ERDE activities induced by BA and PB to a similar extent. Neither PB nor PCN significantly increased AE activity. However, these compounds induced GT2. BA did not affect GT2 but induced GT1. The present results show that the culture of adult rat hepatocytes changes the relative distribution of monooxygenase and GT forms. The response to inducers resembles only partially that observed in vivo.