Effect of starvation on lipoprotein lipase activity in the liver of developing rats

Liver lipoprotein lipase activity in neonatal (1- and 5-day-old) rats was 2-3-times than in the liver of adult rats. In mid-suckling (15-day-old) or weaned (30-day-old) animals, it was not significantly different from the low activity detected in adult rats. Starvation resulted in a 3-fold increase of lipoprotein lipase activity in the neonatal liver, but did not affect the activity in the liver of mid-suckling, weaned or adult rats. When isolated livers from both 1- and 5-day-old pups were perfused with heparin, a sharp peak of lipoprotein lipase activity appeared in the perfusate. In fed neonates, the peak area accounted for about 70% of the total (released + non-releasable) activity. In starved neonates, the proportion of heparin-releasable activity increased up to about 90%. These results indicate that neonatal rat liver lipoprotein lipase activity is markedly affected by changes in the nutritional status of the animal, and the effect is restricted to the vascular pool of the enzyme, as was reported in extrahepatic tissues from adult rats.     

The effect of in vivo treatment with triiodothyronine on the in vitro synthesis of protein-poly(ADP)-ribose adducts by isolated cardiocyte nuclei and the separation of poly(ADP)-ribosylated proteins by phenol extraction and electrophoresis

In vivo treatment of rats with triiodothyronine (30 micrograms/100 g of body weight for 4 consecutive days) inhibited poly(ADP)-ribose polymerase activity of cardiocyte nuclei, but low enzymatic activity of nuclei of noncardiocyte origin remained unaffected. RNA synthesis in cardiocyte nuclei isolated from triiodothyronine-treated rats was augmented. A positive correlation was observed between the degree of inhibition of poly(ADP)-ribose polymerase and cardiac ventricular enlargement in triiodothyronine-treated animals. RNA synthesis in isolated cardiocyte nuclei was inhibited by in vitro poly(ADP)-ribosylation only when cardiocyte nuclei were obtained from triiodothyronine-treated animals. In vitro poly(ADP)-ribosylated proteins were isolated from cardiocyte nuclei by solvent partitioning between phenol and aqueous phases. About 90% of the protein-poly(ADP)-ribose adducts partitioned into the aqueous fraction, and the chain length of polymers in this phase was between medium (n = 4-9) and long (n greater than 32), whereas the phenol phase contained protein-oligomer and monomer adducts. Not only the chain length of oligomers but the nature of modified proteins appeared to participate in determining the partitioning of polymer-protein adducts, and different proteins were separated from the two phases by gel electrophoresis. More than 90% of protein-polymer adducts formed by cardiocyte nuclei were not extracted by 0.25 N HCl, indicating prevalence of nonhistone proteins as polymer acceptors. Gel electrophoresis and near quantitative recovery of adducts in a gel system that protected from degradation of adducts to free polymers confirmed the predominance of nonhistone proteins as main acceptors and demonstrated an artifact of autoradiography that seemed to indicate histone H1 as a significant acceptor. Treatment with triiodothyronine diminished poly(ADP)-ribosylation of certain groups of proteins more than others, implying some degree of selectivity of action of the hormone. Catabolism of the polymer in vitro was not affected by triiodothyronine treatment.     

Quantitative isolation of oligo- and polyadenosine-diphosphoribosylated proteins by affinity chromatography from livers of normal and dimethylnitrosamine-treated Syrian hamsters. In vivo and in vitro metabolism of the homopolymer

Polyadenosine- and adenosine-diphosphoribosylated proteins of hamster liver were quantitatively isolated with the aid of m-aminophenyl boronic acid glutaryl hydrazide polyacrylamide affinity resin by selective adsorption at pH 8.2 and elution at pH 4.0. Polymer-free proteins, DNA, and RNA are readily separated from adenosine-diphosphoribosylated proteins. The total quantity of proteins that is covalently modified by the homopolymer is 14.3 micrograms/mg of DNA or 37.4 micrograms/g of liver in controls and 38.7 micrograms/mg of DNA or 116 micrograms/g of liver in dimethylnitrosamine-treated hamsters. Polymer content increases from 9 to 15 nmol/mg of DNA to 42 to 118 nmol/mg of DNA following treatment with dimethylnitrosamine. Pulse labeling with [14C]ribose results in a parallel doubling in dimethylnitrosamine-treated animals of the specific activities of adenosine- diphosphoribose and NAD+ and of the [14C]ribose content of polyadenosine-diphosphoribose of chain length between 20 and 40, indicating chain elongation of pre-existing larger polymers. Two groups of proteins that are isolated as polyadenosine-diphosphoribose adducts are increased significantly after treatment with dimethylnitrosamine, one minor component of a mass between 100-112 X 10(3) daltons, and a major group exhibiting a mass of 158-162 X 10(3) daltons. Polyadenosine-diphosphoribose synthetase activity of isolated hepatic nuclei is increased by 32-37% after dimethylnitrosamine treatment, and since the change in glycohydrolase activity is negligible relative to the increase in synthetase, the augmentation of polyadenosine-diphosphoribosylated proteins can be explained by the increased synthetase of nuclei. The molecular size distribution of DNA in liver nuclei of control and dimethylnitrosamine-treated hamsters is indistinguishable.     

The activity of deoxyribonucleic acid polymerase and deoxyribonucleic acid synthesis in nuclei from brain fractionated by zonal centrifugation

1. The DNA polymerase (EC 2.7.7.7) activity in purified intact brain nuclei from infant rats was investigated. The effects of pH, Mg(2+), glycerol, sonication and storage of the nuclei under different conditions were examined and a suitable assay system was established. 2. The nuclei from infant brain cells were fractionated by zonal centrifugation in a discontinuous sucrose gradient into five zones: zone (I) contained neuronal nuclei (59%) and astrocytic nuclei (41%); zone (II) contained astrocytic nuclei (81%) and neuronal nuclei (19%); zone (III) contained astrocytic nuclei (82%) and oligodendrocytic nuclei (18%); zone (IV) contained oligodendrocytic nuclei (92%) and zone (V) contained oligodendrocytic nuclei (100%). 3. The content of DNA, RNA and protein for each fraction was measured. 4. The distribution of DNA polymerase activity in the fractionated infant and adult rat brain nuclei was determined. The highest activity was found in the neuronal nuclei from zone (I) and the following zones exhibited a progressive decline. In contrast with the nuclei from infant rats those from adults had a much higher activity and expressed a preference for native DNA as template. 5. The deoxyribonuclease activity in all classes of nuclei was measured with [(3)H]DNA as substrate. A general correspondence in the pattern of the relative activities in the nuclear fractions with the distribution of DNA polymerase was found. 6. The incorporation of [(3)H]thymidine into nuclear DNA in infant and adult rat brain was investigated. The specific radioactivity of the DNA in the 10-day-old rats was highest in zone (V) whereas in the nuclei of adult rats, which exhibited a comparatively low incorporation, the highest specific radioactivity was associated with zones (I) and (V).     

Intracellular distribution of poly(ADP-ribose) synthetase in rat spermatogenic cells

The highest activity of poly(ADP-ribose) synthetase was found in the testis among several rat tissues tested. Subcellular fractionation of the testis demonstrated that the synthetase was localized primarily in the nucleus and partially in the microsomal-ribosomal fraction. This result was confirmed by immunocytochemical staining with the enzyme-specific antibody. The synthetase was localized in the nuclei of interstitial cells, Sertoli cells, spermatogonia, and spermatocytes. In addition, round spermatids showed a granular staining in the cytoplasm, which was comparable in intensity with that in the nucleus. The cytoplasmic synthetase had a molecular weight of 115,000 and synthesized oligomers of ADP-ribose on itself (automodification). The synthetase activity in the isolated cytoplasmic fraction was stimulated about threefold by the addition of DNA and depressed by treatment with DNase I, suggesting the presence of endogenous activator DNA. A candidate DNA for such an activator was isolated from the microsomal-ribosomal fraction, and identified tentatively as mitochondrial DNA on the basis of its size and restriction fragment patterns.     

Comparative analysis of neonatal and adult rat carotid body responses to chronic intermittent hypoxia.

Previous studies suggest that carotid body responses to long-term changes in environmental oxygen differ between neonates and adults. In the present study we tested the hypothesis that the effects of chronic intermittent hypoxia (CIH) on the carotid body differ between neonates and adult rats. Experiments were performed on neonatal (1-10 days) and adult (6-8 wk) males exposed either to CIH (9 episodes/h; 8 h/day) or to normoxia. Sensory activity was recorded from ex vivo carotid bodies. CIH augmented the hypoxic sensory response (HSR) in both groups. The magnitude of CIH-evoked hypoxic sensitization was significantly greater in neonates than in adults. Seventy-two episodes of CIH were sufficient to evoke hypoxic sensitization in neonates, whereas as many as 720 CIH episodes were required in adults, suggesting that neonatal carotid bodies are more sensitive to CIH than adult carotid bodies. CIH-induced hypoxic sensitization was reversed in adult rats after reexposure to 10 days of normoxia, whereas the effects of neonatal CIH persisted into adult life (2 mo). Acute intermittent hypoxia (IH) evoked sensory long-term facilitation of the carotid body activity (sensory LTF, i.e., increased baseline neural activity following acute IH) in CIH-exposed adults but not in neonates. The effects of CIH were associated with hyperplasia of glomus cells in neonatal but not in adult carotid bodies. These observations demonstrate that responses to CIH differ between neonates and adults with regard to the magnitude of sensitization of HSR, susceptibility to CIH, induction of sensory LTF, reversibility of the responses, and morphological remodeling of the chemoreceptor tissue.     

Aminoacylation of rat liver transfer RNA with homologous and heterologous enzyme systems during aging

Total tRNA extracted from livers of young (7 +/- 1 weeks), adult (40 +/- 1 weeks) and old (80 +/- 1 weeks) rats showed quantitative variation with age, being maximal in adults. Young and old animals yielded almost the same level of tRNAs. Quantitative changes in tRNAs were also observed from the study of amino acid acceptor activity using homologous enzyme i.e., aminoacyl-tRNA synthetase preparations from rat liver of the same age group. Quantitative variation followed the trend of qualitative variation. When tRNA was amino-acylated with a heterologous enzyme system, i.e., synthetase preparation from rat liver of another age group, age-related variation in aminoacyl-tRNA did not follow a pattern similar to that in the case of the homologous enzyme system. Young and adult synthetase enzymes showed maximum affinity for their homologous tRNAs but synthetases from old rat liver did not show any specific affinity for "old" tRNAs. This shows that apart from tRNAs, enzyme activity also changes with age.     

Biochemical aspects of cardiac muscle differentiation. Deoxyribonucleic acid synthesis and nuclear and cytoplasmic deoxyribonucleic acid polymerase activity.

DNA synthesis and DNA polymerase activity have been measured in terminally differentiating cardiac muscle of the rat. Incorporation of [3H]thymidine into DNA essentially ceases by the 17th day of postnatal development. Cardiac muscle of neonatal rats contains at least two molecular species of DNA polymerase: a 3.5 S DNA polymerase that can be extracted from nuclei with 0.2 m potassium phosphate and a 6 to 8 S soluble cytoplasmic DNA polymerase. The nuclear DNA polymerase in crude extracts has a pH optimum of 9.0 and is more active with native DNA than with denatured DNA as the primer-template. The cytoplasmic DNA polymerase in crude extracts has a pH optimum of 7.5 and is more active with denatured DNA. The activity of the 6 to 8 S cytoplasmic DNA polymerase decreases 80-fold from day 1 to day 17 after birth, which correlates temporally with the reduced rate of DNA synthesis. The activity of the 3.5 S nuclear DNA polymerase remains relatively constant throughout postnatal development. Mixing experiments (assay of neonatal enzyme extracts with adult enzyme extracts) gave additive results, suggesting that the decline in 6 to 8 S DNA polymerase activity apparently is not due to the presence of absence of soluble activators or inhibitors at different times during development. These studies may provide a system which can be used to investigate the control of DNA synthesis and cellular proliferation during the terminal stages of cardiac muscle differentiation.     

Biochemical aspects of cardiac muscle differentiation. Determination of deoxyribonucleic acid template availability and 3′-hydroxyl termini in nuclei and chromatin by using exogenous deoxyribonucleic acid polymerases

Experiments were designed to determine whether DNA synthesis ceases in terminally differentiating cardiac muscle of the rat because the activity of the putative replicative DNA polymerase (DNA polymerase alpha) is lost or whether the activity of this enzyme is lost because DNA synthesis ceases. DNA-template availability and 3'-hydroxyl termini in nuclei and chromatin, isolated from cardiac muscle at various times during the developmental period in which DNA synthesis and the activity of DNA polymerase alpha are decreasing, were measured by using Escherichia coli DNA polymerase I, Micrococcus luteus DNA polymerase and DNA polymerase alpha under optimal conditions. Density-shift experiments with bromodeoxyuridine triphosphate and isopycnic analysis indicate that DNA chains being replicated semi-conservatively in vivo continue to be elongated in isolated nuclei by exogenous DNA polymerases. DNA template and 3'-hydroxyl termini available to exogenously added DNA polymerases do not change as cardiac muscle differentiates and the rate of DNA synthesis decreases and ceases in vivo. Template availability and 3'-hydroxyl termini are also not changed in nuclei isolated from cardiac muscle in which DNA synthesis had been inhibited by administration of isoproterenol and theophylline to newborn rats. DNA-template availability and 3'-hydroxyl termini, however, were substantially increased in nuclei and chromatin from cardiac muscle of adult rats. This increase is not due to elevated deoxyribonuclease activity in nuclei and chromatin of the adult. Electron microscopy indicates that this increase is also not due to dispersal of the chromatin or disruption of nuclear morphology. Density-shift experiments and isopycnic analysis of DNA from cardiac muscle of the adult show that it is more fragmented than DNA from cardiac-muscle cells that are, or have recently ceased, dividing. These studies indicate that DNA synthesis ceases in terminally differentiating cardiac muscle because the activity of a replicative DNA polymerase is lost, rather than the activity of this enzyme being lost because DNA synthesis ceases.     

Poly(adenosine diphosphate ribose) polymerase activity and nicotinamide adenine dinucleotide in differentiating cardiac muscle.

Poly(ADP-ribose) polymerase activity in nuclei isolated from differentiating cardiac muscle of the rat has been characterized and its activity measured during development. Optimum enzyme activity is observed at pH 8.5. Poly(ADP-ribose) polymerase is inhibited by ATP, thymidine, nicotinamide, theophylline, 3-isobutyl-1-methylxanthine and caffeine and stimulated by actinomycin D. The activity measured under optimal assay conditions increases during differentiation of cardiac muscle and is inversely related to the rate of DNA synthesis and to the activities of DNA polymerase alpha and thymidine kinase. When DNA synthesis and the activity of DNA polymerase alpha are inhibited in cardiac muscle of the 1-day-old neonatal rat by dibutyryl cyclic AMP or isoproterenol, the specific activity of poly(ADP-ribose) polymerase measured in isolated nuclei is increased. The concentration of NAD+ in cardiac muscle increases during postnatal development. In the adult compared with the 1-day-old neonatal rat the concentration of NAD+ relative to fresh tissue weight, DNA or protein increased 1.7-fold, 5.2-fold or 1.4-fold respectively. The concentration of NAD+ in cardiac muscle of the 1-day-old neonatal rat can be increased by approx. 20% by dibutyryl cyclic AMP. These data suggest that NAD+ and poly(ADP-ribose) polymerase may be involved with the repression of DNA synthesis and cell proliferation in differentiating cardiac muscle.     

PROTEIN SYNTHESIS IN FRACTIONS FROM ISOLATED BRAIN CELL NUCLEI

Abstract— 1. The incorporation in vivo and in vitro of isotopically labelled leucine into fractions of nuclear proteins from young and adult rat brain was investigated.
2. During post-natal cerebral maturation, the ability of nuclei from brain cells to synthesize proteins decreased. The specific activities of all the fractions of nuclear protein were highest in 3-day-old rats and declined thereafter. Nuclei from adult brain cells exhibited only 10 per cent of the activity found in nuclei from brain cells of 3-day-old rats.
3. The 'residual protein' fraction was most rapidly labelled, peak activity being reached within 30 min after injection. In vitro , the 'residual protein' fraction attained maximum activity within 40 min.
4. The specific activity of the chromatin acidic proteins (HCl-insoluble) was considerably higher than that of the histones both in vivo and in vitro. Histones were the most inert of all the nuclear protein fractions studied.
The possible functional significance of the various protein fractions during the process of cerebral maturation and in the adult brain is discussed.     

Kinetics of tert-[35S]Butylbicyclophosphorothionate Binding in the Cerebral Cortex of Newborn and Adult Rats: Effects of GABA and Receptor Desensitization

Abstract: The effects of GABA on the kinetics of tert -[³⁵S]butylbicyclophosphorothionate ([³⁵S]TBPS) binding to the convulsant site of GABA_A receptors were studied in membrane suspensions from the cerebral cortex of newborn (1-day-old) and adult (90-day-old) rats. TBPS dissociation was biphasic in neonates and adults, indicating that more than one interconvertible state of [³⁵S]TBPS binding sites may be present in the cerebral cortex. In the absence of GABA, the fast ( t _1/2, 11 min) and slow ( t _1/2, 77 min) components of TBPS dissociation in newborn rats were approximately fourfold slower than in adults. The acceleration of the dissociation rates caused by 2 µ M GABA, however, was more robust in neonates than in adults (six- to ninefold vs. twofold increase, respectively). Moreover, the dissociation rates of TBPS in membranes preincubated with 2 µ M GABA (dissociation started by adding 40 µ M picrotoxin) were two- to fourfold slower than in membranes preincubated without GABA (dissociation started by adding 40 µ M picrotoxin plus 2 µ M GABA). Taken together, these results suggest that (1) the closed state of GABA_A receptors is associated with a more effective steric barrier for the binding of TBPS in neonates compared with adults, (2) GABA produces a larger acceleration of the binding kinetics of TBPS in neonates than in adults, and (3) long incubations with GABA may cause receptor desensitization, which in turn slows down the dissociation rates of TBPS.     

Cerulenin resistance in a cerulenin-producing fungus. II. Characterization of fatty acid synthetase from Cephalosporium caerulens

Cerulenin, an antifungal antibiotic isolated from a culture filtrate of Cephalosporium caerulens, is a potent inhibitor of fatty acid synthetase systems of various microorganisms and animal tissues. This antibiotic specifically blocks the activity of beta-ketoacyl thioester synthetase (condensing enzyme) by binding to the functional cysteine-SH in the active center of the condensing enzyme domain (the peripheral SH-group). However, fatty acid synthetase from C. caerulens is much less sensitive to cerulenin than fatty acid synthetases from other sources. The properties of C. caerulens synthetase were investigated and compared to those of Saccharomyces cerevisiae synthetase, which is sensitive to the antibiotic. The molecular weight of the enzymically active form of C. caerulens synthetase was 2.53 X 10(6). The enzyme consisted of two multifunctional proteins, alpha and beta, which are arranged in a complex, alpha 6 beta 6. The synthetase was inactivated by iodoacetamide. At 0 degrees C and pH 7.15, the second-order rate constant of k = 15.6 M-1 X s-1 was obtained for the inactivation by iodoacetamide. This value was about 15 times greater than that for S. cerevisiae synthetase. Treatment of C. caerulens synthetase with iodoacetamide, while impairing the synthetase activity, induced malonyl-CoA decarboxylase activity. When S. cerevisiae synthetase was preincubated with cerulenin, malonyl-CoA decarboxylase activity could not be detected even after treatment of the enzyme with iodoacetamide (Kawaguchi, A., Tomoda, H., Nozoe, S., Omura, S., & Okuda, S. (1982) J. Biochem. 92, 7-12). In the case of C. caerulens synthetase, on the other hand, malonyl-CoA decarboxylase activity was induced by iodoacetamide even after the preincubation of the enzyme with cerulenin.(ABSTRACT TRUNCATED AT 250 WORDS)     

The occurrence of two types of deoxyribonucleic acid polymerase activity in the main classes of nuclei obtained from the brains of infant and adult rats

1. The influence of exogenous or activated DNA template on the DNA polymerase activity in the different types of intact nuclei from rat brain tissue was determined. The different amounts or physical state of the DNA template did not produce significant differences in the relative distribution of the DNA polymerase activity between the separate groups of nuclei. 2. The DNA polymerase activities, fractionated by sucrose gradient centrifugation into enzyme A and enzyme B, were found to be present in the extracts of all types of rat brain nuclei. The distribution of these two activities in the ;particulate' and ;soluble' fractions of the separate groups of nuclei from 10-day-old and adult rats was studied. The findings are related to the DNA-synthetic activity in vivo of the intact nuclei and the possible biological functions of the DNA polymerase activities are discussed.     

Sarcolemmal ATPase activities of the rat heart ventricle--dependence on age and sodium ion

Na-K-ATPase activity of the rat heart was similar throughout the postnatal growth when measured from crude unpurified fraction. Instead in the cardiac sarcolemmal fraction, isolated by hypotonic shock LiBr-treatment method, the activity was over two times higher in 10-day old neonates than in adult rats. The conflicting results are partly explained by different effects of the isolation procedure on neonatal and adult tissues. Na concentration for half-maximal activity of the Na-K-ATPase was similar in neonates (7.0 mM) and adults (6.4 mM). Ca-ATPase activity was not affected by Na concentration (2-100 mM) in the two age-groups studied.     

Alterations in liver chromatin during perinatal development of the rat

Chromatins were isolated from liver nuclei of 19-day fetuses, 2-, 5-, 21-day old and adult rats. Very little variation was observed in the mass ratio of total histones to DNA or in the spectrum of histones as determined by polyacrylamide gel electrophoresis. On the other hand, the amount and banding pattern of acidic proteins indicated pronounced changes during liver development.The composition of acidic proteins may be specific for the stage of development as evidenced immunochemically. Antibody against acidic protein-DNA complexes from adult rat liver were produced in rabbits. Whereas adult liver acidic protein-DNA complexes interacted strongly with the antibody, fetal liver preparations showed very little affinity. Complexes from 2-day-old animals reacted more strongly than fetal complexes while preparations from 5-day-old and 21-day-old displayed further increases in affinity. The results support the idea that chromatin acidic proteins play an important role in genetic expression during the ontogeny.     

Nuclear deoxyribonucleic acid polymerases of liver.

Hepatic nuclei that are isolated in aquenous solutions of low ionic strength or glycerol contain all or nearly all the nonmitochondrial DNA polymerase activity of the cell. The presence of polymerase activity in the cytoplasm is due to extraction of nuclear enzymes by buffer and inorganic salts. Even with low ionic strength solutions, some leaching of nuclear enzymes occurs if the concentration of liver in the homogenizing medium is greater than 10%. As defined by sucrose gradient analysis, the normal adult rat liver nucleus contains mainly or entirely a single species of DNA polymerase (3.2 S) whereas the regenerating nucleus after 70% hepatectomy has an additional enzyme (7.1 S). The total activity of regenerating nuclei is about twice the normal value. The increase resides in the 7.1 S activity. The 7.1 S DNA polymerase had been purified partially from regenerating liver nuclei (isolated in low ionic strength solutions) and cytosol (prepared under conditions of nuclear enzyme extraction). The properties of the activity from the two sources are indistinguishable. A mixture of albumin and spermidine enhances by several-fold the activities of the 3.2 S and 7.1 S DNA polymerases. In the presence of spermidine, but not in its absence, the activity of the 7.1 S DNA polymerase is strictly proportional to the amount of the enzyme preparation.     

DNA damage induced by hydrogen peroxide in cultured tobacco cells is dependent on the cell growth stage

The level of hydrogen peroxide (H(2)O(2))-induced genomic DNA damage measured by the Comet assay in tobacco suspension cells (TX1) increased as a function of the age of the culture. After treatment of TX1 cells with 15 mM H(2)O(2), the average (+/-S.E.) median tail moment value was only 4.85+/-1.00 microm in nuclei isolated from 2-day-old cells compared to 72.33+/-1.40 microm in nuclei isolated from 12-day-old cells. By contrast, nuclei first isolated from 2 and 12-day-old cells and then treated with H(2)O(2), expressed the same level of DNA damage. The activity of catalases was markedly higher in 2-day-old TX1 cells compared to 12-day-old cells. The results indicate that the reaction of the H(2)O(2) with nuclear DNA is modified by the presence of the plant cell wall, and enzymes and macromolecules present in the cytosol, and is not connected with changes in the nuclear DNA sensitivity during cell suspension growth.     

Different sensitivity of PPARalpha gene expression to nutritional changes in liver of suckling and adult rats

The amount of peroxisome proliferator-activated receptor-alpha (PPARalpha) protein was markedly augmented in the liver of suckling rats compared to adult rats. This different PPARalpha abundance was used to study the sensitivity to nutritional changes in the expression and activity of this receptor. Thus, 10-day-old and adult rats were orally given either glucose, Intralipid or a combination of both diets, and liver mRNA levels of PPARalpha and the PPAR related genes, acyl-CoA oxidase (ACO) and phosphoenolpyruvate carboxykinase (PEPCK), and plasma metabolites were measured. In neonates, the expression of PPARalpha and ACO was seen to increase when the level of FFA in plasma was also high, unless an elevated level of insulin was also present. However, this fatty acid-induced effect was not detected in adult rats. On the contrary, the hepatic expression of PEPCK was modulated by the nutritional changes similarly in both neonates and adult rats. Thus, it may be concluded that the expression of the PPARalpha gene in adult rats seems to be less sensitive to nutritional changes than in neonates.