PubMed Health⌕ Search

Biomedical subjects

R C Reitz

Publications and source records attributed to R C Reitz.

At least 37 records · Page 2Linked to original sources
PubMed1985

Ethanol-induced alterations in rat synaptosomal plasma membrane phospholipids. Relationship to changes in the phospholipid methyltransferases.

The effects of ethanol ingestion on the lipids of the synaptic plasma membrane (SPM) have been measured and correlated with the time frame for the development of physical dependence. Alterations were observed in three of the phospholipid fractions: phosphatidylcholine (PC) increased, and the phosphatidylethanolamine (PE) and phosphatidylserine (PS) plus phosphatidylinositol (PI) fractions decreased. These alterations occurred after the animals showed signs of dependence. Because PC can be synthesized from PE by the methyltransferase pathway, synaptosomal methyl group incorporation was measured. Rats were fed ethanol for 6 days before an increase was observed in methyl incorporation, a shorter length of time than was necessary to demonstrate physical dependence or phospholipid alterations (10 to 14 days). After ethanol withdrawal, 7 days of control diet feeding were required for methyl group incorporation to return to control values. In vitro ethanol (10-250 mM) additions to the methyltransferase incubations resulted in a slight increase in methyl incorporation. These data suggest that synaptic membrane lipid alterations may be related to ethanol dependence and that changes in the PC/PE ratio may be the result of an increase in the incorporation of methyl groups into synaptosomal phospholipids.

Animals↗
PubMed1983

Studies on the half-life and the distribution of stearoyl-CoA desaturase in the housefly.

The half-life of the stearoyl-CoA desaturase was determined by using houseflies injected with puromycin. The LD50 for puromycin was determined to be 1.55 micrograms/mg body wt for both sexes. By following the decay in specific activity of the desaturase after puromycin injection, the half-life of this enzyme in 4-day-old females was calculated to be 9.35 hr, while in 1-day-old females it was 3.38 hr. The inhibition curve for the 3-day-old males never reached 100%, and a biphasic curve was observed. The early phase resulted in a half-life of the desaturase of 2.41 hr, while the latter phase had a half-life of 8.45 hr. In general, it appeared that the half-life of the desaturase increased with age in either sex. Studies on the distribution of desaturase activity within the housefly showed that most of the activity was present in the integument; however, in the female, the onset of ovarian development seemed to shift the distribution of desaturase from the integument, towards the internal tissues. In the male, there appeared to be equal amounts of desaturase in integument and the fat body plus internal tissues at day 2, but by day 5 most of the activity was associated with the integument. The high specific activity and high percentage of total desaturase activity associated with integument coupled with the shift of distribution of desaturase in females during the onset of ovarian development may be indicative of a close correlation of the desaturase with alkene synthesis and possibly sex pheromone production.

Animals↗
PubMed1983

Ethanol ingestion and polyunsaturated fatty acids: effects on the acyl-CoA desaturases.

The ingestion of ethanol results in altered compositions of the polyenoic fatty acids in a variety of liver and brain membranes. A possible cause for these alterations in hepatic endoplasmic reticulum membranes has been studied by measuring the delta 9, delta 6, and delta 5 acyl-CoA desaturase activities in hepatic microsomes from chronically or acutely treated rats. Chronically, ethanol decreased all three enzyme activities with the following order of sensitivity: delta 6 (65%), delta 9 (54%), and delta 5 (46%). The short-term study indicated that all three desaturase activities were affected after 1 day of ethanol feeding. NADPH- and NADH-cytochrome c reductase activities were found to be reduced in chronically treated rats, and the NADH-cytochrome c reductase was decreased in the acutely treated. However, these reduced enzyme activities could not account for the decrease in desaturase activities due to the very marked differences between the specific activities of these enzymes compared to the desaturase. Thus, we conclude that changes in membrane polyenoic fatty acid composition can be result of ethanol-induced decreases in the terminal desaturase enzymes.

Animals↗
PubMed1982

The time-course development of the effects of ethanol ingestion on choline oxidase.

Male rats were fed a low-fat diet containing 36% of calories as ethanol, and the time-course development of the effects of ethanol on liver mitochondrial oxidation of choline was determined. Ethanol induced an increase in choline oxidase at days 2, 5 and 7 after being introduced into the diet. Due to an observed 32% increase in total fatty acids in the whole liver, defatted bovine serum albumin was added to the buffer used to homogenize the liver. The presence of bovine serum albumin resulted in a significant decrease in choline oxidase activity at days 2 and 5; however, ethanol still induced an increase in choline oxidase activity in these mitochondria. The total fatty acid concentration of mitochondria prepared in the absence of bovine serum albumin increased steadily until day 5; however, by day 7 the fatty acid concentration had returned to control levels. The addition of bovine serum albumin to the homogenization medium prevented the increase in the total amount of fatty acids. The fatty acid composition of the bovine serum albumin-treated mitochondria, however, was not different from the mitochondria isolated in the absence of bovine serum albumin. Further, the addition of a free fatty acid to isolated mitochondrial preparations caused about a 100% increase in choline oxidase. These data are consistent with the idea that choline oxidase may be regulated to some extent by an influx or an increase in free fatty acids in the liver as a result of ethanol ingestion. Thus, a second mechanism has been described which contributes to the increase in choline oxidase after ethanol ingestion.

Alcohol Oxidoreductases↗
PubMed1982

Acyl-CoA synthase and acyltransferase activity in developing skeletal muscle membranes.

Enzymes participating in the activation and esterification of fatty acids for complex lipid biosynthesis were characterized in neonatal and adult rabbit skeletal muscle membranes. The activity of acyl-CoA synthase was 1.4-1.6-fold greater in neonatal vs. adult sarcoplasmic reticulum for the fatty acid substrates linoleic (2.6 vs. 1.61 nmol 18:2-CoA/min per mg), stearic (0.94 vs. 0.66 nmol 18:0-CoA/min per mg) and palmitic (2.43 vs. 1.51 nmol 16:0-CoA/min per mg) acids. Enzyme activity was identical between neonate and adult for coenzyme A, ATP and linoleic acid concentration dependence. Glycerol-3-phosphate acyltransferase activity was 6-fold greater in neonatal than adult sarcoplasmic reticulum for both linoleoyl-CoA (1.4 vs. 0.22 nmol 18:2/min per mg) and stearoyl-CoA (1.1 vs. 0.13 nmol 18:0/min per mg) donor substrates, whereas lysophosphatidylcholine acyltransferase activity was similar. Enriched fractions of sarcolemmal membranes possessed the highest activity for lysophosphatidylcholine acyltransferase activity, being 2-4-fold greater than sarcoplasmic reticulum. In contrast to sarcoplasmic reticulum, lysophosphatidylcholine acyltransferase activity was 2-3-fold greater in neonatal compared to adult sarcolemma for lineoleic (18.9 vs. 8.5 nmol 18:2/min per mg) and the stearic (2.8 vs. 0.68 nmol 18:0/min per mg) acid incorporation. The greater capacity of neonatal membranes for acylation by the de novo pathway is in accord with the requirements for neonatal muscle to effect high rates of triacylglycerol and phospholipid synthesis essential for oxidative metabolism and membrane synthesis during postnatal development and growth.

Acyl Coenzyme A↗
PubMed1981

2',3'-cyclic nucleotide 3'-phosphohydrolase in rat liver mitochondrial membranes.

2',3'-Cyclic nucleotide 3'-phosphohydrolase (nucleoside-2':3'-cyclic-phosphate 2'-nucleotidohydrolase, EC 3.1.4.37) activity has been demonstrated in rat liver mitochondria. The enzyme was localized in both the outer and inner mitochondrial membranes but was absent from the intermembrane space and matrix. The mitochondrial (cyclic nucleotide) phosphohydrolase was activated by freezing and thawing and by treatment with digitonin or detergents. It is suggested that (cyclic nucleotide) phosphohydrolase is an integral membrane protein which is buried to a significant degree within the membrane. Atractyloside was found to be a noncompetitive inhibitor of the enzyme both in intact mitochondria and in preparations of the mitochondrial membranes. The enzyme substrate, 2',3'-cyclic adenosine monophosphate, had no effect on the oxidation of exogenous beta-hydroxybutyrate or succinate by intact mitochondria. These findings suggest that 2',3'-cyclic nucleotide 3'phosphohydrolase is more widely distributed than was previously thought and that the enzyme may play a fundamental role in membranes, independent of their specialized structure or functions.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1981

Effects of chronic ethanol ingestion on the activity of rat liver mitochondrial 2',3'-cyclic nucleotide 3'-phosphohydrolase.

Chronic ethanol ingestion induced a 47% increase in the specific activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (nucleoside-2':3'-cyclic-phosphate 2'-nucleotidohydrolase, EC 3.1.4.37) in whole mitochondria. Both inner and outer mitochondrial membranes showed increased (cyclic nucleotide)phosphohydrolase activity, but the inner was increased 94% compared to 67% for the outer. Techniques which disrupt membrane structure increased (cyclic nucleotide)phosphohydrolase activity. After these treatments, whole mitochondria from ethanol-treated animals still showed a 50% increase in activity. This increase may be related either to an inherent increase in the resistance of (cyclic nucleotide)phosphohydrolase to protein degradation or turnover, or to ethanol-induced membrane changes. An increase in (cyclic nucleotide)phosphohydrolase reaction medium pH was observed when freshly isolated, highly-coupled mitochondria were used. The total increase in pH was about 2-fold greater in the controls compared to the ethanol-treated mitochondria. It is suggested that the smaller initial increase in pH and the greater activity of (cyclic nucleotide)phosphohydrolase in the mitochondria from the ethanol-treated animals relate to previously observed changes in the lipid and protein composition of the mitochondrial membranes. In addition, (cyclic nucleotide)phosphohydrolase may represent an excellent marker for membrane integrity.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1981

Effects of chronic ethanol ingestion on liver glycogen phosphorylase in male and female rats.

The effects of chronic ethanol ingestion on a preparation of liver glycogen phsophorylase have been studied. A coupled assay in the direction of glycogenolysis was used. In the absence of AMP, a significant decrease in specific activity was observed in both males (19%) and females (30%). AMP additions stimulated phosphorylase activity and completely obliterated the ethanol-induced decreases in both sexes of animal. Kinetic studies, done in the absence of AMP, showed that only the apparent Vmax had been altered by ethanol. These data suggest that decreases in liver glycogen after chronic ethanol ingestion may not be related to the specific activity of glycogen phosphorylase. Using both glucose and caffeine as negative effectors, addditional studies demonstrated that the inhibitory effects of caffeine had been altered by ethanol in both males and females and that the inhibitory effects of glucose had been altered only in females. Even though the specific activity for phosphorylase did not directly implicate this enzyme in the ethanol-induced decrease in liver glycogen stores, the latter data regarding glucose and caffeine suggest that chronic ethanol ingestion has altererd this enzyme and that differences exist between males and females.

Adenosine Monophosphate↗
PubMed1980

A mechanism for ethanol-induced damage to liver mitochondrial structure and function.

Mitochondria isolated from rats chronically fed ethanol demonstrated a marked inability to produce energy. The respiratory control ratio, the ADP/O ratio and state 3 respiration rates were all decreased. Coupled with other data, a progression of ethanol-induced changes is proposed with site I being altered prior to site II. Quantitation of mitochondrial cytochromes revealed decreases in cytochromes b and aa3 and an increase in c1. Evaluation of respiration activity in relation to temperature showed ethanol-induced changes in the transition temperature (Tf) which may have been related to changes in the lipid composition of the inner membrane. Mitochondrial membranes were separated, and analysis of fatty acids and phospholipids was performed. Various fatty acids were altered in both membranes; however, the outer membrane was altered more severely. A decrease in the arachidonate : linoleate ratio was observed only in the outer membrane; however, there was no ethanol-induced change in degree of unsaturation in either membrane. Phospholipid quantitation showed a reduction of total lipid phosphorous/mg protein in both membrane fractions; however, the inner membrane was most affected. Cardiolipin was the only phospholipid in this membrane which remained unaltered. The evidence indicates that the mechanism for ethanol-induced damage to the liver mitochondrion involves lipid compositional changes as well as changes in cytochromes and possibly other proteins.

Animals↗
PubMed1980

Chronic ethanol ingestion and glycogen metabolism in male and female rats.

Chronic ethanol ingestion decreased liver glycogen levels in both male and female rats; however plasma glucose was decreased only in males. The decreased levels of liver glycogen were related to increases of 42% and 122% in glycogen phosphorylase in males and females, respectively. Both a and b forms of phosphorylase were increased, but the b form was increased more than the a form. Phosphorylase phosphatase was found to be increased 75% and 267% in males and females, respectively. Studies using positive and negative phosphorylase effector molecules indicated that ethanol ingestion may have altered the structure of phosphorylase a and that the degree of alteration was sex related.

Alcoholism↗
PubMed1979

The acyl-CoA desaturases of microsomes from rat liver and the Morris 7777 hepatoma.

We have investigated the role of the microsomal oxidative desaturase in defining the aberrant phosphoglyceride fatty acid composition of hepatomas. The microsomal delta 9-stearoyl-CoA, delta 6-oleoyl(linolenoyl)-CoA, and delta 5-eicosatrienoyl-CA desaturase activities were studied in control and host liver and in the poorly differentiated Morris 7777 hepatoma. The delta 9-stearoyl-CoA desaturase of the hepatoma was significantly decreased (42%) relative to control liver, yet the hepatoma specific activity was twice that of host liver. Additionally, the specific activity of the delta 9-stearoyl-CoA desaturase of the tumor was found to decrease with increasing tumor weight. Also this desaturase was inactivated by freezing and thawing. The delta 6-oleoyl(linolenoyl)-CoA and delta 5-eicosatrienoyl-CoA desaturases of the hepatoma were 39% and 4% of control, respectively. The electron transport components involved in the desaturase system were reduced, although this did not appear to be rate-limiting. In addition, two competing metabolic reactions which could lower the observed desaturase activities, hydrolysis of the thioester and incorporation of substrate acyl-CoA molecules into glycerides, did not appear to be responsible for the lowered desaturase activities of the tumor. Thus, it appears that reduced levels of the desaturases themselves may be responsible for the observed activities. These results indicate that the capacity of the hepatoma to biosynthesize polyunsaturated fatty acids is greatly reduced and this is consistent with the decreased polyene content observed in many neoplasms.

Animals↗
PubMed1979

A possible mechanism for the increased oxidation of choline after chronic ethanol ingestion.

An attempt has been made to determine the location of the site at which the metabolism of ethanol interacts with that of choline to produce an increase in the oxidation of choline. The first enzyme in the oxidation pathway for choline, choline dehydrogenase, was assayed using a newly developed spectrophotometric assay and freshly isolated intact rat liver mitochondria. No changes were observed in either 'apparent' V or the 'apparent' Km values of choline dehydrogenase for choline after ethanol ingestion. However, when the choline oxidase system was assayed, a 28% decrease in 'apparent' Km for choline and a 53% increase in 'apparent' V was observed. The effects of ATP on choline oxidase were studied further, and a 29.4% decrease was observed in mitochondrial ATP levels from freshly isolated mitochondria from the ethanol-treated rats. In vitro aging of mitochondria further decreased the level of ATP, and the rate of decrease was considerably faster during the first hour in the mitochondria from the ethanol-treated animals. The decreases in ATP from both control and experimental mitochondria were accompanied by increases in choline oxidase activity. The initial decrease in ATP was correlated with an increase in mitochondrial ATPase activity which may be related to an increase in mitochondria Mg2+. Because chronic ethanol ingestion has resulted in decreased oxidation rates of succinate and beta-hydroxybutyrate while at the same time increasing the oxidation rates of choline, the studies reported here suggest that the effect of chronic ethanol ingestion is primarily on a step that is unique to choline and which probably exists prior to the electron transport chain.

Adenosine Triphosphatases↗