Biosynthesis of L-ascorbic acid in different sub-cellular fractions of prenatal and postnatal rat livers

Enzyme induction of the early chick embryo by airborne particulate extracts

The induction by airborne particulate extracts of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase (ECOD) in early chick embryos was studied to determine whether or not lethality by the extracts was related to the induction. The optimal pH values for AHH and ECOD were 7.1 and 6.9, respectively, after administering the extracts to early embryos. The AHH inducing capacity was significantly increased 4 h after injection of the extracts, then the value gradually increased. The ECOD inducing ability was similar to that of AHH, although to a lesser extent. Among fractions from the extracts, the neutral fraction was responsible for most of the AHH inducing activity. Two neutral subfractions (N2 and N3), consisting mostly of polycyclic aromatic hydrocarbons (PAH) and their derivatives, had the highest inducing activity. A dose-response relationship was observed between the amounts of the N2 and induction of AHH and ECOD in 8-day-old embryos. When the N2 was administered at different stages of development (days 5-9), the values of induced AHH and ECOD activities increased along with the days of development. Extracts of the smaller airborne particulates (< 1.1 and 1.1-2.0 microns cut-off diameters) had stronger AHH and ECOD inducing abilities than those of the larger, since the former contained high levels of PAH and their derivatives. These results suggested that PAH and their derivatives in the airborne particulates induced AHH and ECOD activities in the early chick embryo. The relationship between the extent of AHH and ECOD inducing activities and that of embryolethality caused by extracts of airborne particulates was not well established.

Activities in chick embryos of 7-ethoxycoumarin O-deethylase and aryl hydrocarbon (benzo[a]pyrene) hydroxylase and their induction by 3,3',4,4'-tetrachlorobiphenyl in early embryos

Basal activities of 7-ethoxycoumarin O-deethylase and aryl hydrocarbon (benzo[a]pyrene) hydroxylase were determined in whole-liver homogenates from chick embryos of different ages, from newly hatched chicks and from chicks a few days old. The enzyme activities increased substantially in chick embryo livers between days five and 10, remained at a fairly constant level until day 19, and reached a peak in activity one day after hatching. The optimal pH value was lower than 7.0 for both enzyme activities. The total increase in activity from day five to one day after hatching was about 300-fold for 7-ethoxycoumarin O-deethylase and about 75-fold for aryl hydrocarbon (benzo[a]pyrene) hydroxylase. Treatment of eggs with 3,3',4,4'-tetrachlorobiphenyl resulted in increased metabolism of both substrates by five-day-old chick embryo livers. The increase in aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity was 14-fold while that of 7-ethoxycoumarin O-deethylase was approximately double.

Effects of the interferon inducing agents tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC) on the hepatic monooxygenase systems of pregnant and fetal rats

Interferon inducing agents, including tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC), are known to depress hepatic cytochrome P-450-dependent monooxygenase systems and the induction of these systems by phenobarbital (PB) and 3-methylcholanthrene (MC) in mature male rats. The current study investigated the effects of tilorone and poly IC on the cytochrome P-450 systems of non-induced, PB-induced, MC-induced and pregnenolonecarbonitrile (PCN)-induced pregnant rats and their fetuses. Pregnant rats received either tilorone or poly IC and saline, PB, MC or PCN, and microsomes from their livers and those of their fetuses were examined for cytochrome P-450 content, aminopyrine (AP) N-demethylase activity and benzo[a]pyrene (BP) hydroxylase activity. The generalization can be made from these studies that, when the interferon inducing agents caused changes in cytochrome P-450 content or monooxygenase activities of either induced (PB, MC or PCN) or non-induced (saline) animals, decreases were seen in maternal livers and increases in fetal livers. Thus, in maternal livers tilorone depressed cytochrome P-450 and AP N-demethylase activity in non-induced and PB-, MC- and PCN-induced rats and BP hydroxylase activity in the induced animals; BP hydroxylase activity was not depressed in non-induced maternal livers. Poly IC depressed cytochrome P-450 and AP N-demethylase activity in non-induced and PB-induced rats but not in PCN-induced animals. BP hydroxylase was depressed by poly IC in both PB- and PCN-induced animals. Fetal hepatic cytochrome P-450 and monooxygenase activities were increased by tilorone in PB- and PCN-induced rats but not in non-induced or MC-induced animals. Poly IC increased cytochrome P-450 and both monooxygenase activities in PB- and PCN-induced fetal livers, whereas only BP hydroxylase activity was increased in the fetuses of non-induced rats. Several possible explanations are offered for the opposite effects produced by interferon inducing agents in maternal and fetal livers. Unlike maternally administered tilorone, which induced fetal cytochrome P-450 and monooxygenase activities in the liver, intrauterine tilorone depressed cytochrome P-450 and had no effect on AP N-demethylase or BP hydroxylase activities in the fetal liver. Intrauterine poly IC was without effect on the cytochrome P-450 systems of the fetal liver. Treatment of pregnant rats with tilorone on days 17-20 of gestation inhibited normal maternal weight gain and produced overt signs of toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Ontogenetic development of L-gulonolactone oxidase activity in several vertebrates

Activity of L-gulonolactone oxidase (EC 1.1.3.8) in livers of fetal Rattus norvegicus and Mus musculus was detectable on the 18th day of gestation, increased rapidly to maxima at 15 and 5 days postpartum for the two species, respectively, and thereafter declined to adult levels. L-Gulonolactone oxidase was not detectable in liver or kidney of fetal guinea pigs at any stage of development. Near-term fetal snowshoe hares had higher activities of liver L-gulonolactone oxidase than observed in a large sample of adults. L-Gulonolactone oxidase was detectable in chicken (Gallus gallus) embryos by the sixth day of incubation, increased rapidly in the kidney with no discontinuity at hatching, reached a maximum at about the 35th day from the beginning of incubation, and then declined to adult levels. Barn swallow (Hirundo rustica) embryos appeared to synthesize little if any L-ascorbic acid; nestlings had considerably higher levels of L-gulonolactone oxidase than adults. Tadpoles of three species of frogs had appreciable levels of L-gulonolactone oxidase activity.

Hepatic microsomal drug oxidation and electron transport in newborn infants

Many drugs require oxidative metabolism for termination of action and/or for elimination from the body. Many oxidative reactions are catalyzed by hepatic microsomal enzymes. The activities of various drug-metabolizing enzymes, namely, NADPH cytochrome c reductase, NADPH oxidase, aminopyrine-N-demethylase, and analine P-hydroxylase, and the content of cytochrome P-450, were measured in hepatic microsomes obtained from seven newborn infants and four adult patients. The results in the newborn infant show increasing activities of these enzymes (except aminopyrine-N-demethylase) related to advancing age. Good correlation between three components of the hepatic microsomal mixed function oxidase system and aniline p-hydroxylase was established, whereas only NADPH oxidation correlated with aminopyrine N-demethylation. The rate of substrate or drug oxidation and the activities of the components of the microsomal electron transport pathway were lower than comparable values in the adult. The data demonstrate a possible biochemical basis for the transient deficiency in drug metabolism seen in newborn infants.

Biogenesis of endoplasmic reticulum membranes. I. Structural and chemical differentiation in developing rat hepatocyte

The development of the endoplasmic reticulum of rat hepatocytes was studied during a period of rapid cell differentiation, i.e., from 3 days before to 8 days after birth. Before birth, the ER increases in volume, remaining predominantly rough surfaced; after birth, the increase continues but affects mainly the smooth-surfaced part of the system. These changes are reflected in variations of the RNA/protein and PLP/protein ratios of microsomal fractions: the first decreases, while the second increases, with age. The analysis of microsomal membranes and of microsomal lipids indicates that the PLP/protein ratio, the distribution of phospholipids, and the rate of P(32) incorporation into these phospholipids show little variation over the period examined and are comparable to values found in adult liver. Fatty acid composition of total phosphatides undergoes, however, drastic changes after birth. During the period of rapid ER development in vivo incorporation of leucine-C(14) and glycerol-C(14) into the proteins and lipids of microsomal membranes is higher in the rough-than in the smooth-surfaced microsomes, for the first hours after the injection of the label; later on ( approximately 10 hr) the situation is reversed. These results strongly suggest that new membrane is synthesized in the rough ER and subsequently transferred to the smooth ER.