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Abstract: Precision-cut rat liver slices are a widely accepted in vitro tool for the examination of drug metabolism, enzyme induction or hepatotoxic effects of xenobiotics. After prolonged incubation, however, distinct histopathological changes and increasing losses in function are seen with liver slices from adult animals. Since tissue from neonatal animals is expected to be less vulnerable, in the present study liver slices from 1-day-old rats were examined for morphological changes and for the expression of different cytochrome P450 (CYP) isoforms after incubation for up to 24h and after a 24h in vitro exposure to β-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) or pregnenolone 16α-carbonitrile (PCN). In parallel, CYP activities were assessed by different model reactions in slice homogenates and in intact slices. Histopathological changes were less pronounced in liver slices from 1-day-old rats than in those from adult animals. During the 24h of incubation even a maturation of the tissue occurred, since the proportion of haemopoietic stem cells declined and the glycogen content of the hepatocytes increased. The CYP expression pattern after 2 and 24h of incubation was similar to that of normal liver specimens from neonatal rats showing a moderate CYP1A1, 2B1 and 3A2 expression. The immunostaining for CYP1A1 and 2B1 was elevated after incubation with BNF. PB enhanced CYP2B1 and 3A2 expression, and DEX and PCN increased CYP3A2 immunostaining. This induction pattern was paralleled by respective effects on the corresponding model reactions. Thus, besides increased viability, slices from neonatal rats are excellently suited for the evaluation of an in vitro induction of CYP enzymes as well. [Copyright &y& Elsevier]

We previously reported that PLA2 activity in the gills is higher than that in other tissues in red sea bream and purified PLA2 from the gills belongs to the group IB PLA2 as well as other red sea bream PLA2s. In this study, we reconfirmed that the level of PLA2 activity is extremely high in the gills compared with other tissues, and gill PLA2 was detected only in the gills by immunoblotting and inhibition test using anti-gill PLA2 monoclonal antibody. The level of PLA2 activity and protein expression in the gills are well correlated. Fish can be roughly divided into high and low groups based on the level of PLA2 activity. Gill PLA2 was detected in the gills of the high group, but not the low group by immunoblotting. In the gills of the high group, gill PLA2 was detected in the mucous cells and pavement cells located on the surface of gill epithelia by immunohistochemistry. On the other hand, positive signals were observed only in the mucous cells by in situ hybridization. We also isolated inactive proPLA2, having AR propeptide, preceding the mature enzyme from the gill extract. These results suggest that gill PLA2 is synthesized as an inactive proPLA2 in the mucous cells and is secreted to the surface of gill epithelia. [Copyright &y& Elsevier]