Effects of alcohol (ethanol) on the fetus

Alcohol (ethanol) use during pregnancy can produce a wide spectrum of effects in the developing embryo/fetus that are dependent on the maternal drinking pattern. The effects of chronic ethanol exposure on the developing conceptus are reviewed with primary focus on ethanol teratogenesis, manifesting in the human as the fetal alcohol syndrome or fetal alcohol effects. The effects of acute ethanol exposure on the near-term fetus are described, including suppressed fetal breathing movements, electrocorticographic (ECoG) activity and electrooculographic (EOG) activity. The ethanol-induced suppression of fetal breathing movements is a very sensitive index of acute exposure of the near-term fetus to ethanol, and appears to involve a direct mechanism of action rather than an indirect mechanism involving suppression of electrocortical activity. The disposition of ethanol and its pharmacologically active proximate metabolite, acetaldehyde, and the activity of alcohol dehydrogenase and aldehyde dehydrogenase in the near-term maternal-fetal unit are described, and a pharmacokinetic model is proposed. The effects of short-term ethanol exposure on the near-term fetus include the development of tolerance to the ethanol-induced suppression of fetal breathing movements, low-voltage ECoG activity and EOG activity. The development of tolerance occurs more rapidly to the latter two fetal biophysical activities. The mechanism of tolerance development appears to be pharmacodynamic (functional) in nature, as there is no increase in the rate of ethanol elimination from the maternal-fetal unit. The role of prostaglandins (PGs) in the mechanism of the ethanol-induced suppression of fetal breathing movements is described. In the near-term fetus, there is a direct relationship between fetal blood ethanol concentration and fetal plasma PGE2 concentration, and an inverse relationship between the incidence of fetal breathing movements and each of fetal plasma and fetal cerebrospinal fluid (CSF) PGE2 concentrations. Indomethacin, a PG synthetase inhibitor, selectively blocks and reverses the ethanol-induced suppression of fetal breathing movements. These data support the postulates that the ethanol-induced suppression of fetal breathing movements is mediated by increased PGE2 concentration in the near-term fetus and that the ability of indomethacin to antagonize the ethanol-induced suppression of fetal breathing movements is due to its biochemical action to decrease fetal PGE2 concentration.(ABSTRACT TRUNCATED AT 400 WORDS)     

The role of maternal alcohol damage on ethanol teratogenicity in the rat

To study the severity and degree of in utero alcohol effects in relation to the rate of maternal alcohol damage, multiparous 1-year alcohol-fed rats were used, with an appropriate pair-fed control group. During pregnancy, alcoholic dams showed relatively high acetaldehyde levels (41 +/- 19 mumol/l) and blood alcohol levels of 22.8 +/- 14 mmol/l. They also showed marked histological alterations in liver as well as high serum aspartate-aminotransferase, alanine-aminotransferase, alkaline phosphatase, glutamate dehydrogenase, and gamma-glutamyltransferase activities. The increase in serum enzyme levels did not correlate with an increase in hepatic enzyme levels since only glutamate dehydrogenase was enhanced in liver after 1 year of alcohol intake. In addition, except for an increase in low Km aldehyde dehydrogenase activity, there were no changes in liver alcohol metabolizing enzymes in chronic alcohol vs. pair-fed females. Alcoholic rats showed a high incidence of damage in their progeny (resorptions, immature fetuses, decrease in fetal weight, etc.), and rats with the highest serum levels of the above enzymes (especially glutamate dehydrogenase and gamma-glutamyl transferase) had severely affected progeny. Rats with minimal histological liver damage, in contrast, did not show resorptions. Thus, the results presented suggest that the stage of maternal alcohol illness, as indicated mainly by the extent of liver damage, plays an important role in the frequency and severity of in utero alcohol effects in the rat.     

Effect of acetaldehyde on ethanol- and aldehyde-metabolising systems of the liver and brain of rats

Lately the mechanism of craving for alcohol has been related to the local level of brain acetaldehyde occurring in ethanol consumption and depending on the activities of the brain and liver ethanol and acetaldehyde-metabolizing systems. In this connection, we studied the effect of chronic acetaldehyde intoxication on the activities of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), the microsomal ethanol oxidizing system (MEOS) and liver and brain catalase as well as ethanol and acetaldehyde levels in the blood. The results showed that the chronic acetaldehyde intoxication did not alter significantly the activities of liver ADH, MEOS and catalase as well as liver and brain ALDH. In parallel with this, the systemic acetaldehyde administration led to shortened time of ethanol narcosis and activation of catalase in the cerebellum and left hemisphere, which may indicate involvement of this enzyme into metabolic tolerance development.     

Polyamines and diamine oxidase activity in maternal, embryonal, and fetal tissues of rat after chronic ethanol consumption

The effects of maternal ethanol consumption for 4 weeks before and throughout gestation on polyamine content and diamine oxidase activity of maternal, embryonal and fetal tissues are reported. At the 12th day of pregnancy, a decrease of putrescine in the liver of the mother and marked increases in putrescine, cadaverine and spermidine in embryos were observed. At day 18, putrescine and cadaverine diminished in maternal liver and placenta, and no changes in amine content in fetal liver and brain were found. At day 12, diamine oxidase activity increased in maternal liver and placenta, whereas it greatly diminished in embryos. At day 18, enzyme activity decreased in maternal liver, placenta, fetal liver and brain. These results indicate that chronic ethanol ingestion induces alterations in polyamine concentrations and metabolism in growing and developing tissues during pregnancy that might contribute to the adverse effect of ethanol on conceptual development.     

Effect of acute, multiple-dose ethanol on maternal and fetal blood gases and acid-base balance in the near-term pregnant ewe

The effect of ethanol on maternal and fetal blood gases and acid-base balance was determined in six conscious instrumented near-term pregnant ewes for maternal intravenous infusion of 3 g ethanol/kg total body weight administered as six doses of 0.5 g ethanol/kg total body weight over 8 h. Maternal and fetal blood ethanol concentrations, determined in two animals, were maximal at 8 h (3.74 and 3.82 mg/mL, respectively) and were virtually identical during the 24-h study. Maternal and fetal blood gases and acid-base balance were not significantly altered during and after ethanol administration compared with preinfusion values. The data demonstrate that, during near-term ovine pregnancy, the equivalent of a binge-type drinking episode does not produce fetal hypoxia or acidosis. Furthermore, these data do not support the postulated involvement of ethanol-induced fetal hypoxia in the mechanism of ethanol teratogenesis.     

An enzymatic model for rat liver alcohol dehydrogenase in the presence of low-Km aldehyde dehydrogenase

Four isoenzymes of aldehyde dehydrogenase were partially purified from rat liver mitochondria by hydroxylapatite chromatography and gel filtration. While three forms display low affinity for acetaldehyde, the fourth is active at extremely low aldehyde concentrations (Km less than or equal to 2 microM) and allows the oxidation of the acetaldehyde formed by catalysis of alcohol dehydrogenase at pH 7.4. Different models of alcohol dehydrogenase have been examined by analysis of progress curves of ethanol oxidation obtained in the presence of low-km aldehyde dehydrogenase. According to the only acceptable model, when the acetaldehyde concentration is kept low by the action of aldehyde dehydrogenase, NADH no longer binds to alcohol dehydrogenase, but acetaldehyde still competes with ethanol for the active site of the enzyme. The seven kinetic parameters of the two enzymes (four for alcohol dehydrogenase and three for aldehyde dehydrogenase) and the equilibrium constant of the reaction catalyzed by alcohol dehydrogenase have been determined by applying a new fitting procedure here described.     

Aldehyde dehydrogenase (EC 1.2.1.3): comparison of subcellular localization of the third isozyme that dehydrogenates gamma-aminobutyraldehyde in rat, guinea pig and human liver.

1. Subcellular fractionation of rat, guinea pig and human livers showed that aldehyde dehydrogenase metabolizing gamma-aminobutyraldehyde was exclusively localized in the cytoplasmic fraction in all three mammalian species. 2. Total gamma-aminobutyraldehyde activity of aldehyde dehydrogenase was found to be ca 0.41, 0.3 and 0.24 mumol NADH min-1 g-1 tissue, respectively in rat, guinea pig and human liver, with more than 95% of activity in the cytoplasm. 3. Partially purified cytoplasmic isozyme from rat liver showed similar chromatographic behavior and kinetic properties to the E3 isozyme isolated from human liver. 4. The rat isozyme was insensitive to disulfiram (40 microM) and to magnesium (160 microM) and had Km values of 5 microM (pH 7.4) for gamma-aminobutyraldehyde, 7.5 microM (pH 9.0) for propionaldehyde and 4 microM (pH 7.4) for NAD.     

In vivo ethanol elimination in man, monkey and rat: a lack of relationship between the ethanol metabolism and the hepatic activities of alcohol and aldehyde dehydrogenases

The in vivo ethanol elimination in human subjects, monkeys and rats was investigated after an oral ethanol dosage. After 0.4 g. ethanol/kg of body weight, ethanol elimination was much slower in human subjects than in monkeys. In order to detect a rise in monkey plasma ethanol concentrations as early as observed in human subjects, ethanol had to be administered at a dose of 3 g/kg body weight. Ethanol metabolism in rats was also much faster than in human subjects. However, human liver showed higher alcohol dehydrogenase activity and higher low Km aldehyde dehydrogenase activity than rat liver. Thus, our data suggest a lack of relationship between hepatic ethanol-metabolizing activities and the in vivo ethanol elimination rate.     

Alcohol and acetaldehyde in rat's milk following ethanol administration

Alcohol and acetaldehyde were measured in milk and peripheral blood in chronic alcoholic rats, at 5 and 15 days of lactation. Ethanol in blood increased throughout lactation and the levels of acetaldehyde were much higher than in nonlactating alcoholic rats. The concentration of acetaldehyde in milk was always ca. 50% of that in blood, whereas that of ethanol varied within the range of 44-80% of the blood levels. Blood alcohol levels in the corresponding sucking pups were much lower than in maternal blood and increased throughout lactation. The time course of ethanol and acetaldehyde concentration in blood and milk were determined in normal lactating rats after cyanamide (40 mg/kg) and ethanol administration (2 or 4 g/kg). Milk alcohol reached higher concentrations than in blood within the first hour of ethanol administration, decreasing and remaining constant thereafter at ca. 65% of those in blood. Acetaldehyde levels in milk were always 35-45% lower than in blood. No alcohol dehydrogenase activity was found in homogenates of mammary tissue; however there was some aldehyde dehydrogenase activity. A significant decrease in mammary tissue aldehyde dehydrogenase was found in chronic alcoholic rats. The role of this enzyme is discussed.     

Decreased ethanol consumption by rats as affected by central alpha-adrenoblockaders: the role of liver aldehyde dehydrogenase isoenzymes

It has been shown in the experiments on rats that subcutaneous administration of central alpha-adrenoblockers IEM-611 (30 mg/kg and 15 mg/kg) and phenoxybenzamine (10 mg/kg) for one or two weeks brings about a decrease in voluntary ethanol consumption at early stages of experimental alcoholism (3-week alcoholization). In rats with chronic alcoholization for 6 months only IEM-611 had a remarkable inhibitory effect on alcohol consumption. Moreover, it has been stated that IEM-611 reduced threefold the activity of liver aldehyde dehydrogenase (AlDH) by the inhibition of AlDH isoenzymes with low and high Km for acetaldehyde. Phenoxybenzamine inhibited slightly only low Km AlDH. It is suggested that differences in IEM-611 and phenoxybenzamine effects may be associated with specific drug inhibition of AlDH isoenzymes.     

Activities of hepatic enzymes related to ethanol oxidation and effects of ethanol on hepatic metabolites in rats with chronic liver injury.

To study the effects of ethanol on liver chronically injured by CCl4, activities of hepatic enzymes related to ethanol oxidation, influences of ethanol on hepatic metabolites, and blood ethanol disappearance were observed. (1) Activities of alcohol dehydrogenase, low- and high-Km aldehyde dehydrogenase, microsomal ethanol-oxidizing system and drug-metabolizing enzyme were remarkably decreased in the injured liver. (2) Increases in lactate/pyruvate and beta-hydroxybutyrate/acetacetate ratios were shown in control liver 2 h after ethanol ingestion. Similar but less pronounced effects of ethanol on the 'redox state' were also seen in rats with chronic liver injury. (3) Delay in ethanol disappearance was not observed until 12 h after ethanol ingestion. The ethanol-induced changes in the redox state in the injured liver were similar to those in controls. Higher ethanol concentrations in blood from rats with chronic liver injury could be related to potentiate the injured liver.     

Ethanol metabolism in guinea pig: In vivo ethanol elimination,alcohol dehydrogenase distribution,and subcellular localization of acetaldehyde dehydrogenase in liver

Guinea pig ethanol metabolism as well as distribution and activities of ethanol metabolizing enzymes were studied. Alcohol dehydrogenase (ADH; EC 1.1.1.1) is almost exclusively present in liver except for minor activities in the cecum. All other organ tissues tested (skeletal muscle, heart, brain, stomach, and testes) contained only negligible enzyme activities. In fed livers, ADH could only be demonstrated in the cytosolic fraction (2.94 μmol/g liver/min at 38 °C) and its apparent K_m value of 0.42 mm for ethanol as substrate is similar to the average K_m of the human enzymes. Acetaldehyde dehydrogenase (ALDH; EC 1.2.1.3) of guinea pig liver was measured at low (0.05 mm) and high (10 mm) acetaldehyde concentrations and its subcellular localization was found to be mainly mitochondrial. The total acetaldehyde activity in liver amounts to 3.56 μmol/g/ min. Fed and fasted animals showed similar zero-order alcohol elimination rates after intraperitoneal injection of 1.7 or 3.0 g ethanol/kg body wt. The ethanol elimination rate of fed animals after 1.7 g ethanol/kg body wt (2.59 μmol/g liver/min) was inhibited by 80% after intraperitoneal injection of 4-methylpyrazole. Average ethanol elimination rates in vivo after 1.7 g/kg ethanol commanded only 88% of the totally available ADH activity in fed guinea pig livers. Catalase (EC 1.11.1.6), an enzyme previously implicated in ethanol metabolism, is of 3.4-fold higher activity in guinea pig (10,400 U/g liver) than in rat livers (3,100 U/g liver), but 98% inhibition by 3-amino-1,2,4-triazole did not significantly alter ethanol elimination rates. After ethanol injection, fed and fasted guinea pigs reacted with prolonged hyperglycemia.     

Effects of alcohol consumption on mitochondrial aldehyde dehydrogenase isoenzymes in rat liver

The effects of long-term and short-term exposure of rats to ethanol on aldehyde dehydrogenase (ALDH) activity in the liver mitochondria were investigated. The specific activities of mitochondrial high Km ALDH and low Km ALDH after the prolonged administration of ethanol were both increased to levels about 2.5 times that of the control group. In contrast, high Km and low Km ALDH showed maximum activity 12 h after administration of a single large dose of ethanol, increasing 21 and 4.4 times, respectively, over the level in the control group. When ethanol was administered for a long time, the two ALDH isoenzyme levels showed approximately the same increase, while the high Km ALDH level was more significantly increased than the low Km ALDH level after a single large dose. These results suggest that the high Km ALDH level of the outer membrane was increased as a result of a transient increase in the level of acetaldehyde around the liver mitochondria after a single large dose of ethanol, and that high Km ALDH plays an important role in acetaldehyde metabolism. However, when ethanol was administered for a long time, the mitochondria were exposed to low concentrations of acetaldehyde over a long time, leading to an increase in levels of low and high Km ALDH in the matrix.     

METABOLIC CONSEQUENCES OF ETHANOL OXIDATION IN BRAINS FROM MICE CHRONICALLY FED ETHANOL

Abstract— Effects of the acute and chronic administration of ethanol have been investigated in mouse brain on the redox-state, citric acid cycle function, levels of adenine nucleotides and other metabolites. Cerebral oxidation of ethanol, activity of alcohol dehydrogenase and the permeability of brain and liver mitochondrial preparations after chronic ethanol administration have been also investigated. Acute or chronic administration of ethanol resulted in a small but significant increase in the reduced components of certain dehydrogenase-linked substrate pairs in brain. Pyrazole, an inhibitor of alcohol dehydrogenase, prevented the ethanol-induced changes in brain. ¹⁴CO₂ production from several substrates was inhibited in brains from chronically ethanol-fed animals. Addition of pyrazole, however, prevented the ethanol-mediated inhibition of ¹⁴CO₂ production. Chronic administration of ethanol resulted in decreased levels of ATP and creatine phosphate in the brain, and increased contents of ADP and AMP. The cerebral activities of alcohol dehydrogenase and succinic dehydrogenase, oxidation of ethanol, mitochondrial oxidation of a-glycerophosphate, and levels of NADH remained unaffected by the chronic administration of ethanol. In contrast to liver, where chronic administration of ethanol increased the contribution of 'substrate shuttles'resulting in increased oxidation of ethanol; in brain, the contribution of these 'shuttles'remained unaffected.     

Evidence for opiate receptor binding in rat small intestine

The influence of ethanol consumption during pregnancy on maternal-fetal transfer of amino acid was studied. Pregnant rats were fed a liquid diet containing 30% ethanol-derived calories from gestation-day 6 to 21; control rats were pair-fed identical diets, except that sucrose substituted isocalorically for ethanol. On gestation-day 21, 2 uCi/100 g body weight of ¹⁴C-alpha-aminoisobutyric acid (¹⁴C-AIB) was injected into the maternal circulation, and 90 minutes later maternal blood and liver, placentas and fetuses were removed for radioactivity measurement. No differences between ethanol-fed and control rats in the distribution of ¹⁴C-AIB in maternal plasma or the uptake of ¹⁴C-AIB by the maternal liver were observed. However, the radioactivities in placenta and fetal tissues suffered a significant 20 to 40% reduction in the ethanol-fed group, suggesting that ethanol feeding during pregnancy impairs placental function.     

Studies on the ontogenesis and the regulatory mechanisms of placental lactogen and insulin binding sites (receptor) in rat liver

The ontogenesis of specific binding of 125I-hPL and 125I-insulin was determined in rat liver cell membranes (10(5) X g pellets), and the regulatory mechanisms of these binding sites were also examined. There were striking differences in the mode of ontogenesis between binding sites of hPL and insulin in rats. HPL binding sites were very few in liver cell membranes from fetal and immature rats. They began to increase after puberty, and markedly increased in late pregnancy. On the other hand, insulin binding sites, which decreased in late pregnancy, were dominant in fetal liver and placenta. Consequently, the lipolytic and glycogenolytic activities of hPL in maternal liver were accentuated, whereas the effects of insulin on maternal liver were suppressed. In contrast, in fetal liver and placenta only the anabolic effects of insulin seemed conspicuous. According to the results of experiments on in vivo administration of estradiol-17 beta, progesterone, hydrocortisone or hPL to intact or hypox-rats, and the measurement of serum rat chorionic mammotropin (rCM), rPRL, estradiol-17 beta, and insulin during pregnancy in rats, the increase in hepatic hPL binding sites observed in late pregnancy might be, at least in part, due to rCM secreted from placenta, and the decrease in insulin binding sites due to the increase in serum insulin itself in rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Placental transport of free palmitic and linoleic acids in the guinea pig

Radioisotopic tracers were used to measure the unidirectional transfer rates of free fatty acids across the placenta of fed and fasted pregnant guinea pigs. Free (14)C-labeled palmitic and linoleic acids (in serum) were injected simultaneously into a jugular vein of an anesthetized pregnant guinea pig. Serial samples of maternal blood were collected from a carotid artery; fetal blood was collected from the umbilical vein of an exposed fetus. Analysis of maternal and fetal plasma revealed that: (a) the half-lives of free palmitic and linoleic acid in maternal plasma are approximately 1.3 min and 0.7 min, both in fed animals with low plasma concentrations of these acids and in fasted animals with high concentrations; (b) free linoleic and palmitic acids cross the placenta from maternal to fetal plasma in a ratio of approximately 2.0, a value which appears not to change as the transfer rates of these acids from maternal to fetal plasma are increased by fasting the mother. It is suggested that the ratio in which free linoleic and palmitic acids cross the placenta from maternal to fetal plasma is determined by the ratio of the unbound free linoleic and palmitic acid concentrations in maternal plasma. A comparison of several species indicates that a much greater proportion of fetal fatty acids comes from the mother in the guinea pig and rabbit than in the rat, the sheep, or man.     

Hepatic alcohol dehydrogenase activity in chick hepatocytes towards the major alcohols present in commercial alcoholic beverages: comparison with activities in rat and human liver

We have compared hepatic alcohol dehydrogenase activities in chick, rat and human liver with the major alcohols in commercial alcoholic beverages. 1. Chick and rat hepatic alcohol dehydrogenase was greater when assayed at a physiological pH in buffer containing chloride ions, as compared with the activity in pyrophosphate buffer at alkaline pH. 2. In contrast to reports of instability of ADH to freezing, we found the enzyme from all three species stable to freezing in 0.25 M sucrose. 3. Rat liver enzymatic activity was unstable in the presence of substrate, where as that of chick and human was not. 4. For all three species, the Km of hepatic ADH for substrate decreased with increasing chain length of alcohols. In both chick and human samples, the Vmax values for the higher chain alcohols were similar to that with ethanol, while in rat samples, ADH activity was dramatically lower with the higher chain alcohols compared to ethanol.     

Development of tolerance to ethanol-induced suppression of breathing movements and brain activity in the near-term fetal sheep during short-term maternal administration of ethanol

The effect of short-term maternal ethanol administration on the ethanol-induced suppression of fetal breathing movements, electrocortical (ECoG) activity, and electroocular (EOG) activity was determined in the near-term fetal sheep. Twelve conscious instrumented pregnant ewes (between 125 and 139 days of gestation; term, 147 days) received 1-h intravenous infusion of 1 g ethanol/kg total body weight daily for six days (n = 6) or an equivalent volume of normal saline daily for six days (n = 6). On the seventh day, the ethanol- and saline-pretreated animals were administered 1 g ethanol/kg total body weight. A further six ewes received 1-h intravenous infusion of 1 g ethanol/kg total body weight (n = 3) or an equivalent volume of normal saline (n = 3) daily for thirteen days with both groups receiving 1 g ethanol/kg total body weight on day fourteen. Fetal ECoG and EOG activities, and fetal breathing movements were monitored continuously over the post- operative and experimental periods. Saline infusion had no significant effect on the parameters studied. Fetal breathing movements were suppressed for 8 h after the first ethanol dose, and were not significantly suppressed after fourteen days of once-daily, maternal ethanol administration. Low-voltage ECoG and EOG activities were suppressed for 3 h after the first ethanol dose, and were not significantly suppressed after seven days of repeated ethanol administration. Maternal and fetal blood gases and acid-base balance were not significantly affected by maternal ethanol administration. These data demonstrate that short-term maternal administration of ethanol results in the development of tolerance to ethanol in the mature fetus.     

Enzymatic oxidation of phthalazine with guinea pig liver aldehyde oxidase and liver slices: inhibition by isovanillin

The enzymes aldehyde oxidase and xanthine oxidase catalyze the oxidation of a wide range of N-heterocycles and aldehydes. These enzymes are widely known for their role in the metabolism of N-heterocyclic xenobiotics where they provide a protective barrier by aiding in the detoxification of ingested nitrogen-containing heterocycles. Isovanillin has been shown to inhibit the metabolism of aromatic aldehydes by aldehyde oxidase, but its inhibition towards the heterocyclic compounds has not been studied. The present investigation examines the oxidation of phthalazine in the absence and in the presence of the inhibitor isovanillin by partially purified aldehyde oxidase from guinea pig liver. In addition, the interaction of phthalazine with freshly prepared guinea pig liver slices, both in the absence and presence of specific inhibitors of several liver oxidizing enzymes, was investigated. ldehyde oxidase rapidly converted phthalazine into 1-phthalazinone, which was completely inhibited in the presence of isovanillin (a specific inhibitor of aldehyde oxidase). In freshly prepared liver slices, phthalazine was also rapidly converted to 1-phthalazinone. The formation of 1-phthalazinone was completely inhibited by isovanillin, whereas disulfiram (a specific inhibitor of aldehyde dehydrogenase) only inhibited 1-phthalazinone formation by 24% and allopurinol (a specific inhibitor of xanthine oxidase) had little effect. Therefore, isovanillin has been proved as an inhibitor of the metabolism of heterocyclic substrates, such as phthalazine, by guinea pig liver aldehyde oxidase, since it had not been tested before. Thus it would appear from the inhibitor results that aldehyde oxidase is the predominant enzyme in the oxidation of phthalazine to 1-phthalazinone in freshly prepared guinea pig liver slices, whereas xanthine oxidase only contributes to a small extent and aldehyde dehydrogenase does not take any part.