F.A. de la Iglesia

The effect of phenobarbital and carbon tetrachloride on fatty acid content and composition of phospholipids from the endoplasmic reticulum of rat liver

Abstract The fatty acid content and composition of hepatic microsomes of separated smooth and rough components and of isolated phosphatidylcholine and phosphatidylethanolamine fractions were studied in male albino rats treated with phenobarbital or carbon tetrachloride. Both test compounds significantly altered the fatty acid composition of the endoplasmic reticulum. The total amount was significantly raised by phenobarbital and reduced by carbon tetrachloride. Phenobarbital enhanced palmitic, stearic, arachidic, palmitoleic, linoleic, eicosenoic, eicosadienoic, eicosatrienoic, eicosapentenoic, docosatrienoic, and docosahexenoic acids. Carbon tetrachloride diminished all these, excluding palmitic and palmitoleic acids. The fatty acid content of rough microsomes was significantly increased by phenobarbital and decreased by carbon tetrachloride, while in smooth microsomes fatty acids were raised by phenobarbital but mainly unaffected by carbon tetrachloride. In microsomal phosphatidylcholine fractions, phenobarbital significantly elevated oleic, linoleic, eicosatrienoic, arachidonic, eicosapentenoic, docosapentenoic, and docosahexenoic acids, whereas all these were significantly reduced with carbon tetrachloride. In phosphatidylethanolamine fractions, phenobarbital increased palmitoleic, oleic, linoleic, and arachidonic acids; carbon tetrachloride elicited opposite effects on these acids. Phenobarbital increased and carbon tetrachloride reduced the fatty acid content in the phosphatidylcholine fraction of rough membranes. Opposite effects were seen in oleic, linoleic, arachidonic, and eicosapentenoic acids. Both test compounds brought about similar changes in the fatty acid composition of the phosphatidylethanolamine fractions of rough microsomes. In smooth microsomes, phosphatidylcholine fatty acids were significantly enhanced by phenobarbital and reduced by carbon tetrachloride. The fatty acid content of phosphatidylethanolamine was increased by phenobarbital, mainly manifesting in palmitoleic, oleic, linoleic, arachidonic, docosapentenoic, and docosahexenoic acids. Carbon tetrachloride elicited no major change in this fraction. Phenobarbital increased the production of unsaturated fatty acids, whereas carbon tetrachloride elevated the relative amount of saturated fatty acids. The saturated/unsaturated fatty acids ratio was reduced by phenobarbital and increased by carbon tetrachloride, and thus may indicate a selective difference between an inducer and hepatotoxin on fatty acid synthesis of the hepatic endoplasmic reticulum.

The effect of phenobarbital and carbon tetrachloride on fatty acid content and composition of phospholipids from rat liver.

Abstract The administration of phenobarbital or carbon tetrachloride to rats caused various changes in hepatic fatty acid content and composition. Phenobarbital elicited no effect on the total amount of fatty acids but significantly decreased myristic, pentadecanoic, and arachidonic acids and increased eicosatrienoic, eicosapentenoic, lignoceric, and docosatrienoic acid. In contrast, carbon tetrachloride enhanced significantly the total content and several components such as pentadecanoic, palmitic, palmitoleic, oleic, linoleic, arachidic, eicosenoic, eicosadienoic, eicosatrienoic, docosapentenoic, lignoceric and docosahexenoic acids. It elicited no effect on arachidonic acid. Unsaturated fatty acid moieties participating in the structure of these phosphatides were increased by phenobarbital and diminished by carbon tetrachloride. Phenobarbital caused a reduction in the ratio of saturated/unsaturated fatty acids mainly because of the decreased palmitic and increased oleic, linoleic, eicosatrienoic, arachidonic, docosapentenoic, and docosahexenoic acids. The significant variation brought about by phenobarbital and carbon tetrachloride on tissue fatty acids and in particular on fatty acid composition of phosphatidylcholine and phosphatidylethanolamine fractions reflects the opposing effects of these compounds on the liver cell. The major action of phenobarbital and carbon tetrachloride is associated with changes of the endoplasmic reticulum. Thus, their contrasting effect on fatty acid composition and metabolism may suggest that the disposition of lipid constituents plays a determinant role in the hepatic action of foreign compounds.

Coumarin and 4-methylcoumarin induced changes in the hepatic endoplasmic reticulum studied by quantitative stereology

Coumarin and 4-methylcoumarin constitue chemicals widely available in foodstuffs and coumarin-induced hepatotoxicity has been characterized in laboratory animals. The present studies were undertaken to analyze the effects of these compounds on the structure of endoplasmic reticulum membranes. The liver of rats treated for seven days with 1 mmole/kg of either coumarin or 4-methylcoumarin were subjected to quantitative sterologic analysis and various morphometric parameters were determined. Coumarin induced cytoplasmic enlargement while 4-methylcoumarin produced changes in the endoplasmic reticulum and Golgi aratus (GOL) without altering cell size. Both compounds caused a significant overall reduction of smooth-surfaced (SER) membranes. Since 4-methylcoumarin stimulates drug metabolism, this indicates that conformational changes must have taken place in the membrane arrangement. On the other hand, the reduction of membranes by coumarin is accompanied by reduced enzyme activity and phospholipid metabolism, suggesting an impairment of membrane synthesis mircosopical examinations provides a useful and sensitive tool to study the effects of foreign compounds in the liver.

Effect of drugs on progesterone metabolism in the female rat

Various drugs brought about a reduction of serum progesterone level irrespective of whether or not a potent inducer (phenobarbital, 4-methyl-coumarin) or a hepatotoxin (carbon tetrachloride, alpha-naphthylisothiocyanate, coumarin) has been administered. The decrease by hepatotoxins was highly significant during the estrus phase of the cycle. These treatments affected the hepatic level of progesterone and altered the uptake of [4-14C]progesterone in vivo. The serum level of progesterone was significantly decreased by phenobarbital and carbon tetrachloride; however, the incorporation into the liver was enhanced by phenobarbital and reduced by carbon tetrachloride. This opposing hepatic action showed selectivity; phenobarbital increased the oxidative pathway of progesterone metabolism (formation of 6 beta-, 16 alpha-, 20 alpha-hydroxyprogesterone) but the reductive pathway remained unaltered (formation of pregnanediol, pregnanolone). Conversely, carbon tetrachloride diminished oxidation and raised reduction of progesterone. These results have been confirmed by measurements of progesterone metabolism in vitro using isolated microsomes. Phenobarbital brought about an induction of progesterone 16 alpha-, 6 beta- and 20 alpha-hydroxylase, did not affect progesterone delta 4-5 alpha-dehydrogenase, whereas carbon tetrachloride inhibited hydroxylase and raised dehydrogenase activities. The action of these test compounds on serum and liver levels of progesterone and on the variation of progesterone metabolism seemed to be related to changes manifest in the function of the hepatic endoplasmic reticulum. Similar changes might be associated with the development of mild hepatic lesions induced by various steroids.

Effects of progesterone metabolites on fatty acids of the hepatic endoplasmic reticulum membranes

Abstract The effect of 2 selected progesterone metabolites on the phospholipid fatty acid composition of the liver and microsomal function was studied in the female rat. 16α-Hydroxyprogesterone significantly increased microsomal phospholipid content and the total amount of fatty acids esterified to phospholipids parallel with aminopyrine N -demethylase activity. Phospholipid changes were attributable to phosphatidylcholine and phosphatidylethanolamine. Both saturated and unsaturated fatty acids were enhanced. In contrast, 5β-pregnane-3α-ol-20-one caused a reduction of microsomal phospholipids, phosphatidycholine, together with decreased aminopyrine N -demethylase activity and total microsomal fatty acid content. Pregnanolone decreased both saturated and unsaturated fatty acids and its action on unsaturated acyl components was greater than on the saturated ones. Changes in fatty acids were manifested in palmitic, stearic and lignoceric acids among saturated fatty acids and in palmitoleic, oleic, linoleic, eicosaenoic, eicosadienoic, eicosatrienoic, arachidonic, eicosapentenoic, docosatrienoic, docosapentenoic and docosahexenoic acids among unsaturated ones. Total liver phospholipids were unaltered by either 16α-hydroxyprogesterone or 5β-pregnane-3α-ol-20-one. These test compounds, however, modified total hepatic fatty acid content. 16α-Hydroxyprogesterone increased total fatty acids and both saturated and unsaturated acyl components, whereas 5β-pregnane-3α-ol-20-one decreased these parameters. Major changes were manifested in saturated fatty acids such as stearic, arachidic and lignoceric acids, and in unsaturated ones such as palmitoleic, linoleic, eicosatrienoic and docosapentenoic acids. The action of these compounds on phospholipid fatty acids of hepatic microsomes may be causally related to their effect on drug-metabolizing activity of the endoplasmic reticulum.

Phospholipids in the liver of the pregnant rat: Changes in fatty acid content and composition

Abstract Pregnancy in the rat was associated with changes in hepatic phospholipids. All changes returned to the prepregnancy levels 2 to 3 weeks postpartum. The total phospholipid content was reduced significantly, mainly representing a reduction of phosphatidylcholine, -ethanolamine, and lysophosphatidylcholine fractions. Hepatic fatty acid content was also reduced and the composition was modified since both saturated and unsaturated acyl components were decreased with more pronounced changes in unsaturated acids. Total liver saturated fatty acids with 14 to 16 carbon atoms remained unaltered; stearic acid was reduced and arachidic and lignoceric acids were elevated. Among unsaturated fatty acids, palmitoleic, oleic, eicosatrienoic, arachidonic, eicosapentaenoic, and docosapentaenoic were decreased, docosatrienoic and docosahexaenoic were raised, whereas eicosaenoic and eicosadienoic did not change. In the phosphatidylcholine and -ethanolamine fractions, unsaturated acyl components also showed significant reduction. By and large they reflected the fatty acid changes occurring in total liver with the exception of the docosahexaenoic acid which was diminished in both fractions. The overall effect of pregnancy thus indicated a modification in unsaturated fatty acid content leading to the construction of less fluid membranes which may be responsible for the reduced enzyme activity of the endoplasmic reticulum.

Fatty acid content and composition of phospholipids bound to the hepatic endoplasmic reticulum of the rat: Effect of pregnancy

Abstract Phospholipid and fatty acid content were decreased and fatty acid composition of hepatic microsomes was altered in the rat during pregnancy. These changes were reversible 2 to 3 weeks after parturition. Pregnancy-related fatty acid changes were mainly localized in phosphatidylcholine and -ethanolamine fractions. Both saturated and unsaturated fatty acids were altered, but the reduction of the unsaturated fraction was more pronounced. Saturated acyl components, such as palmitic, stearic, and lignoceric acids, and unsaturated ones, including palmitoleic, oleic, linoleic, eicosatrienoic, arachidonic, and eicosapentaenoic acids, were significantly decreased, whereas only docosahexaenoic acid was elevated. Fatty acid changes were greater in the unsaturated components in phosphatidylcholine and -ethanolamine fractions. The largest reduction was in palmitic, palmitoleic, stearic, oleic, linoleic, arachidonic, and eicosahexaenoic acid content. Pregnancy-related changes in fatty acid distribution and content, and in phospholipid fractions reflect a modified organization and disposition of the hepatic endoplasmic reticulum membranes. These membrane changes represent essentially topographical factors influencing the function and enzymatic activity of these membranes.

ASSOCIATION BETWEEN MEMBRANE FUNCTION AND PHOSPHOLIPID COMPOSITION IN THE HEPATIC ENDOPLASMIC RETICULUM: EFFECT OF DEVELOPMENT

The development of enzyme activity of the hepatic endoplasmic reticulum in the rat was correlated with corresponding changes in PL 2 synthesis, particularly in PC, PE, SM and LPC fractions. Acyl components of membrane-bound PL were raised in both sexes; unsaturated components such as oleic, linoleic, arachidonic and docosapentaenoic acids were relatively enhanced, whereas saturated components such as palmitic, stearic and arachidic acids were relatively reduced. Thus, maturation of these membranes is connected with the synthesis of selective PL fractions that contain greater amounts of unsaturated fatty acids, indicating that bound PL are not only essential in the assembly of membrane structure but exert an important role in the functional organization.

ASSOCIATION BETWEEN MEMBRANE FUNCTION AND LIPID COMPOSITION IN THE HEPATIC ENDOPLASMIC RETICULUM: EFFECT OF PREGNANCY

Pregnancy caused a reduction of PL 2 fatty acid content and modified fatty acid composition of hepatic microsomes in the rat. These changes were not found 2-3 weeks after parturition. Pregnancy-related changes in fatty acids were mainly localized in PC and PE fractions. Saturated and unsaturated fatty acid patterns were altered but the reduction of unsaturated components was more pronounced. PC and PE fractions also revealed greater changes in the unsaturated components. These pregnancy-related changes in fatty acid moieties of microsomal phospholipid may reflect a modified organization and disposition of the hepatic endoplasmic reticulum membranes.

FUNCTIONAL CHANGES OF HEPATIC ENDOPLASMIC RETICULUM BY ADVERSE DRUG TREATMENT

An experimental model with cobalt chloride and phenobarbital to induce “hypofunctional” membranes was used to characterize the proliferated hepatic endoplasmic reticulum membranes in the absence of elevated microsomal activity. Functional studies revealed hepatotoxicity, increases in microsomal protein and phospholipids. Ultrastructure showed pronounced increase in liver cell size, SER comparable to controls, and RER without volume changes. Biochemical data indicated a hyperplastic response of microsomal structural components with reduced enzyme activity and did not correlate with SER proliferation microscopically. These findings implied that some membrane rearrangement took place, perhaps predisposing a compromise of cell integrity, in particular of those reactions requiring oxidative enzymes.