The quantitation of liver cytochrome P450-LM2 mRNA in rabbits of different ages and after phenobarbital treatment

Developmental changes in the amount and functional state of UDP-glucuronosyltransferase

The effect of postnatal development on the activity of liver microsomal UDP-glucuronosyltransferase was determined in male Wistar rats between 25 and 200 days of age using p-nitrophenol as aglycone. Enzyme activity (measured at 1.0 mM UDP-glucuronic acid, 0.05 mM p-nitrophenol) decreased 55% between 25 and 88 days of age and was constant thereafter. Treatment of microsomes with palmitoyl-lysophosphatidylcholine, which allows for an estimation of the amount of enzyme, showed approximately a four-fold decrease in enzyme concentration during the same period. This decrease was confirmed by Western blotting of microsomes with anti-UDP-glucuronosyltransferase antiserum. The fact that a nearly four-fold decline in enzyme concentration led to only a 55% decrease in activity indicates that there was an increase in activity per molecule of UDP-glucuronosyltransferase as the concentration of enzyme decreased. Treatment of microsomes with high pressure or detergent caused a greater extent of enzyme activation in microsomes prepared from 25 than 200 day old rats, suggesting that a fraction of the enzyme in older rats was activated in untreated microsomes. Fatty acid analysis of liver microsomal lipids during postnatal development revealed changes in docosahexaenoic acid (22:6) which correlated with levels of UDP-glucuronosyltransferase activity.

The influence of ageing on the induction of the mRNAs of rat liver cytochromes P450IIB1 and P450IIB2

To investigate the influence of age on the regulation of the cytochromes P450IIB1 and P450IIB2 the levels of the messenger RNAs for these two cytochromes were determined in liver cytoplasmic RNA of rats of various ages after maximal induction with either phenobarbital or isosafrole and in untreated rats. The levels of these mRNAs were determined by solution hybridization with a RNA-probe (riboprobe system) complementary to both mRNAs. This study showed a marked decrease in the maximal induction levels of these mRNAs between the ages of 12 and 36 months irrespective of the type of inducer used. To assess whether this age-related decrease could be found for both individual mRNAs also solution hybridization experiments were performed with deoxyoligonucleotide probes of a defined sequence. The data presented in this paper show that ageing influences the levels of both the cytochrome P450IIB1 and P450IIB2 mRNA in a similar way. After induction the amount of mRNA for P450IIB1 was in all age groups measured four- to five-fold higher than that of P450IIB2. These data indicate that previously observed age-related changes in the cytochrome P450 system could be related to a lower accumulation of its mRNAs.

The influence of age on the inducibility of rat liver cytochrome P450IA1 (CYPIA1) and P450IA2 (CYPIA2) mRNAs

The levels of the messenger RNAs for the cytochromes P450IA1 (CYPIA1) and P450IA2 (CYPIA2) were determined in liver cytoplasmic RNA of rats of various ages after maximal induction with either 3-methylcholanthrene or isosafrole and in untreated rats. An increase in the CYPIA1 mRNA levels was observed only after treatment with 3-methylcholanthrene, whereas both 3-methylcholanthrene and isosafrole were able to induce the levels of CYPIA2 mRNA. The study presented here shows that the maximal induction of these 2 mRNAs did not change with age when 3-methylcholanthrene was used as the inducing agent. Isosafrole induction did not yield higher CYPIA1 mRNA levels in young rats but reduced the amount of this mRNA in old animals to levels below the detection limit of our assay. After induction with isosafrole the levels of the CYPIA2 mRNAs in the older age groups were lower than those observed in young rats. It is concluded that with age the responsiveness to cytochrome P450 inducers may change. This change is different for the various cytochrome P450 enzymes and depends on which inducer is used.

Genetic expression of complement factors and alpha 1-acid glycoprotein by liver tissue during senescence

The effect of age on several messenger RNAs coding for non-specific immune factors were determined in liver RNA isolated from 6-, 12-, 24-, 29- and 37-month-old male Fischer Rats. The levels of complement factors C3 and C4, complement protein factor B, and alpha 1-acid glycoprotein were determined by dot blot hybridization using cDNA probes. All four mRNAs increased slightly between 6 and 29 months of age. Only the mRNAs coding for complement factors C3 and C4 decreased significantly after 29 months of age. In addition, Northern blot analysis of the RNA preparations showed that the size of the four mRNA species did not change with increasing age. There was no evidence for age-related changes in the post-transcriptional processing or degradation of the mRNA species coding for complement factors C3 and C4, complement protein factor B, and alpha 1-acid glycoprotein.