The ability of
3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), 3,5-diethoxycarbonyl-4-ethyl-1,4-dihydro-2,6-dimethyl
pyridine (EDDC) and
griseofulvin to induce
porphyria in primary cultures of mouse and rat hepatocytes was determined. Exposure of mouse hepatocytes to DDC, EDDC or
griseofulvin (5-100 mum) for 4 days resulted in a marked inhibition of
ferrochelatase activity (up to 95%). However, whereas exposure of rat hepatocytes to DDC or EDDC (5-100 mum) for 4 days also resulted in marked inhibition of
ferrochelatase activity (up to 96%), exposure to
griseofulvin (5-100 mum) had no effect. DDC, EDDC and
griseofulvin induced
porphyrin accumulation in both mouse and rat hepatocyte cultures. In mouse hepatocyte cultures exposed to each
xenobiotic the
porphyrin that accumulated was predominantly
protoporphyrin. In rat hepatocyte cultures exposed to DDC or EDDC the
porphyrin that accumulated was also predominantly
protoporphyrin, whereas following exposure to
griseofulvin it was coproporphyrin. Time course studies confirmed that in rat hepatocyte cultures exposed to
griseofulvin (25 or 100 mum) over a 4-day exposure period,
ferrochelatase activity was not inhibited and coproporphyrin was always the predominant
porphyrin accumulating (45-72% of total). Addition of 5-aminolaevulinic
acid to mouse or rat hepatocyte cultures (10-1000 mum) also resulted in marked accumulation of
porphyrin but whereas uroporphyrin accumulated in mouse hepatocyte cultures, coproporphyrin accumulated in rat hepatocyte cultures. These studies demonstrated that the
hepatic porphyrias produced by the
dihydropyridines and
griseofulvin can be modelled in vitro in primary cultures of hepatocytes. Furthermore, the species differences in sensitivity of mouse and rat hepatocyte cultures in vitro to inhibition of
ferrochelatase activity by
griseofulvin mirrors, and therefore probably explains, the species differences in
porphyria observed in vivo.