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Stimulation of prostacyclin synthesis in rats treated with phenobarbital
Pmstaglandins, Leukolrienes and Medicmr N’ Longman Group UK Ltd 1987
(1987) 28. 267-275
Stimulation of Prostacyclin Synthesis in Rats Treated with Phenobarbital Ali 2. Haghighi and Thomas I. Pynadath Department of Chemistry, Kent State University Kent, Ohio 44242 (reprint requests to TIP) ABSTRACT The effect of phenobarbital treatment on the synthesis of prostacyclin in coronary vascular microsomes was studied in Sprague Dawley rats. It was found that the treatment increased the synthesis of prostacyclin by nearly 100%. The treatment also resulted in an increase in HDL and a decrease in LDL in the serum. In vitro effects of HDL and LDL on the microsomal synthesis of prostacyclin showed that the synthesis was stimulated by HDL and,inhibited by LDL. Hence it appears that the increase in prostacyclin synthesis resulting from phenobarbital treatment was at least partly due to increased level of HDL and decreased level of LDL in the serum. INTRODUCTION Prostacyclin (PSI 1, synthesized in the endothelial cells of the arteries & the prostacyclin synthetase enzyme system, has been shown to inhibit the aggregation of the platelets in the blood (1). Experimental atherosclerosis has been shown to be associated with a suppression of the synthesis of prostacyclin in the coronary vascular bed (2). Studies in vitro have shown that physiological concentrations of low density lipoprotein (LDL) inhibited the synthesis of PGI2 in pig arotic microsomes while similar concentrations of high density lipoprotein (HDL) stimulated the synthesisof pG12 (3). Thus, relative levels of LDL and HDL in the blood seem to have a considerable effect on the synthesis of prostacyclin in the endothelial cells. Hence it is likely that factors that would affect the levels of LDL and HDL in the blood will have a marked
267
effect on the synthesis prostacyclin. Phenobarbital has been shawn to increase the serum levels of HDL in both humans and rats (4,5). Hence this study was undertaken to determine the effect of phenobarbital treatment on the synthesis of prostacyclin. MATERIALS AND METHODS Spwye_lf awley rats were obtained from the Holtzman Company. C-arachidonic acid was purchased from the New England Nuclear Corporation, and authentic 6-keto-PGFl, was obtained from the Sigma Chemical Company. %enty three month old Sprague Dawley rats, weighing approximately 300 g, were divided into two equal groups and fed Laboratory Purina Rat Chow and water ad libitum. The experimental group was given daily intraperetonial injections of sodium phenobarbital (6 mg/lOO g body weight) in saline solution, for two days, while the control group received placebo injections of the saline solution. ar mlcrosomes. Vascular microsomes were prepared from the heart tissue. Rats from both groups were sacrificed 24 hours after the last injection of phenobarbital or saline solution and the heart tissue was collected from each animal and homogenized in 10 ml volume of oxygenated Kreb's buffer. The homogenates were then centrifuged at 700 x g for 10 min to sediment the nuclei and the debris. The supernatant was further centrifuged at 31,000 x g for 30 min to remove the mitochondria and most of the lysosomes. The supernatant containing mostly the microsomes was used as the enzyme preparation for the incubations. Protein was assayed by the Lowry method (6). . The assay of PGI synthesis was o the method of De inska-Kiec et al (2), by measuring the incorporation of l-rniC-arachidonic acid into 6-keto-PGFlu, the stable decomposition product of PGI2, when the labeled acid was incubated with the microsomal preparation. The incubation mixture contained 5 f microsomal protein and 35.2 nmole (0.06 UC) of ;"laC-arachidonic acid in Kreb's buffer, in a total volume of 2.1 ml. The incubation was carried out for 30 min at 37'C and the reaction was terminated by adjusting the pH to 3.0 by adding 0.5 M HCl. The contents were then passed three times through 3.0 g of XAD-2 amberlite resin packed in a narrow glass column to get all the acidic lipids including the 6-keto-PGFl, adsorbed on the resin (7). After washing off all the unadsorbed contaminants with
268
distilled water, the adsorbed lipids were eluted from the column with four 3-ml volumes of methanol. The pooled methanol extract was evaporated to dryness under a stream of nitrogen and the residue obtained was redissolved in 0.2 ml volume of chloroform-methanol (2:1, v/v). The prostaglandins in the residue were then separated by thin layer chromatography using Silica Gel 60F thin layer plates, using an ethyl acetate/iso-octane/acetic acid/water (11:5:2:1O,v/v) solvent system (8). The radioactive 6-keto-FGFl, spot, identified by cochromatography with non-radioactive authentic 6-Keto-FGF ci,was cut out from the chromatogram and its radioactivi4 determined using a liquid scintillation counter. Statistical analysis of the data was carried out by Student's t-test and results were expressed as mean $_ standard error of the mean (S.E.M.) RESULTS ect of_&&noba&,&&J on pI;I-svnthe is pGI2 synthesis by the coronary vascular microEomes of'th;!control and phenobarbital-treated rats are shown in Table 1. Phenobarbital treatment resulted in a marked increase in the synthesis of FG12 in the microsomes. The increase in the PG12 synthesis resulting from two days of phenobarbital treatment was nearly 100%. Table 1 Effect of phenobarbital treatment on PG12 synthesis by coronary vascular microsomes.
Animals Control (n = 13) 63.9 + 8.1
PB-treated
ect of -1 twnt on wum llnoorotejg_s. Serum lipoprotein composition was determined
269
semi-quantitatively by separating the lipoproteins of the serum, prestained with Sudan Black, by polyacrylamide disc electrophoresis and then scanning the gel at 610 nm in an autointegrating densitometer (9). The results are shcwn in Table 2. Phenobarbital treatment resulted in a significant increase in HDL and decrease in LDL. The HDL increase was nearly 16% while the LDL decrease was more than 30%. No significant change was observed in the VLDL fraction. Table 2 Effect of phenobarbital treatment on serum lipoproteins.
.
Animal group VLDL
ln comnosition (%) HDL LDL
Control
15 + 6 (n = 10)
20 &-4 (n = 10)
65 5 7 (n,= 10)
PB-treated
10 + 6 (n = 9)
14 * 4 (n = 10)
76 k 8 (n = 10)
(p
Addition
Amount added (mg/ml)
PGI synthesis (pmole3mg prot./30 min)
None LDL
HDL
1269 + 157 0.5 1.0 1.5 2.0
1091 939 786 660
+ 140 * 107 it 98 + 92
0.25 0.50 0.75 1.00
1446 1675 1776 1992
+ + + +
(p
270
132 148 145 151
of LDL and HDL on &I- Svnthpai The in vitro effect of LDL and HbL on the synthesis of PSI2 is shown in Table 3. The effect was determined as described by Beitz et al (3) at four different concentrations of each LDL and HDL. The amount of HDL or LDL added was measured in terms of the cholesterol content of the lipoproteins. LDL had a significant inhibitory effect on the PSI synthesis. At the highest concentration of the LDL studie2, the synthesis was inhibited by about 40%. The difference in the degree of the inhibition between two consecutive concentrations was statistically significant (P
271
not known at the present time. One probability is that phenobarbital is involved in the induction of one OK more enzymes involved in the synthesis of prostacyclin. It is well established that phenobabital induces the synthesis of proteins and enzymes in many tissues, especially the liver (16-21). Another probability is that the observed effect of phenobarbital on PGI synthesis is an indirect one. Previous studies have s8 own that phenobarbital treatment increases the HDL level and decreases the LDL level in the serum (4,s). The data of the present study has confirmed these findings. It has shown further that HDL stimulates the synthesis of PGI while LDL inhibits the synthesis. Beitz and Forster (23) have already demonstrated that HDL has a stimulatory effect on the synthesis of PGI in the vascular microsomes of pig. Hence, it appears t at the stimulation of PGI synthesis resulting from the phenobarbital trea8ment was at least partly due to the effect of the increased level of HDL in the serum.
2
Still another explanation for the observed stimulation of EG12 synthesis is the one suggested by Ku et al (2) and Needleman et al (24). These investigators observed that some of the dKUgS they studied stimulated the synthesis of prostacyclin while inhibiting the synthesis of thromboxane. They suggested that this was due to a drug induced shift in the metabolism of PGH2 in the system in such a way that it stimulated the synthesis of prostacyclin from PGH2 at the expense of the synthesis of thromboxane. Phenobarbital which stimulates prostacyclin synthesis and inhibits thromboxane synthesis (15) may be operating in a similar manner. Whatever the mechanism is, phenobarbital appears to have antithrombotic properties since it stimulates prostacyclin synthesis. In addition, it may also have antiatherogenic activity since it increases blood HDL level.. ACKNOWLEDGEMENT The authors thank Dr. Frederick Walz for his generous gift of phenobarbital. REFERENCES 1.
Moncada S, Grylewski R, Bunting S, Vane JR. An enzyme isolated from arteries transformed prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation, Nature 263: 663, 1976.
272
2.
Dembinska-Kiec A, Gryglewska T, Zmuda A, Gryglewski RI. The generation of prostacyclin by the coronary vascular bed is reduced in experimental atherosclerosis in rabbits. Prostaglandins 14: 1025, 1977.
3.
Beitz J, Forster W, Influence of human low density and high density lipoprotein cholesterol on the in vitro prostaglandin I2 synthetase activity. Biochim. Biophys. Acta 620: 352, 1980.
4.
Durrington PN. Effect of phenobarbital on plasma high-density-lipoprotein cholesterol in normal subjects, Clinical Science 56: 501, 1979.
5.
Chao YS, Pickett CB, Yamin TT, Alberts AW, Kroon PA. Phenobarbital induces rat liver apolipoprotein A-I 1985. mRNA. Molecular Pharmacology 27: 394,
6.
Lowry Oliver H, Rosebrough Nira J, Farr Lewis A, Randall Rose J. Protein measurement with the folin phenol reagent. J. Biol. Chem. 193: 265, 1951.
7.
Keirse M, Turnbull A. Extraction of prostaglandins from human blood. Prostaglandins 4: 607, 1973.
8.
Cottee F, Flower RJ, Flower JA, Vane JR. Synthesis of by ram seminal vesicle microsomes. 6-keto-PGF Prostaglanhins 14: 413, 1977.
9.
Naito KM, Wada M, Ehrhart LA, Lewis LA. Polyacrylamide gel disc electrophoresis as a screening procedure for serum lipoprotein abnormalities. Clin. Chem. 19: 228, 1973.
10.
Duguid JB. Thrombosis as a factor in the pathogenesis of aortic atherosclerosis. J. Path. Bact. 60: 57, 1948.
11.
Hand RA, Chandler AB. Atherosclerotic metamorphosis of autologous pulmonary thromboemboli in the rabbit. Am. J. Path. 40: 469, 1962.
12.
Woolf N, Bradley JW, Crawford T, Carstairs KC. Experimental mural thrombi in the pig aorta: The early natural history. Br. J. Exp. Pathol. 49: 257, 1968.
273
13.
Mitchell JR, Schwartz CJ. The relationship between myocardial lesions and coronary artery disease II: A selected group of patients with massive cardiac necrosis or scarring. Br. Heart J. 25: 111963.
14.
Moncada S, Vane JR. Pharmacology and endogenous roles of prostaglandin endoperoxides, thromboxane A2, and prostacycin. p. 293 in Pharmacological Reviews (PL Munson, ed) Williams and Wilkins Company, Baltimore, Maryland, 1978.
15.
Pynadath TI, Haghighi AZ. Inhibition of thromboxane A2 synthesis in rats treated with phenobarbital. Prostaglandins, Leukotrienes and Med. In press.
16.
Depierre JW, Seidegad J, Morgentern R, Balk L, Mesjer J, Astorm A. Induction of drug-metabolizing enzymes: a status report. p. 585 in Mitochondria and Microsomes (C Lee, G Schatz, G Dallner, eds.) Addison-Wesley Publishing Company, Reading, Massachusetts, 1981.
17)
Hilton J, Sartoreli AC. Induction by phenobarbital of microsomal mixed oxidase enzymes in regenrating rat liver. J. Biol. Chem. 245: 4187, 1970.
18)
Pfeil H, Bock KW. Electroimmunochemical qwtification of UDP-glucuronosyltransferase in rat liver microsomes. Eur. J. Biochem. 737: 619, 1983.
19)
Liu KD, and Owens GF. Phenobarbital enhances 2', 5'-oligoadenylate synthesis in rat liver nuclei. Biochem. Biophys. Res. Comm. 121: 788, 1984.
20)
Redinger RN and Smal DM. The effect of phenobarbital upon bile salt synthesis and pool size, biliary lipid secretion, and bile composition. J. Clin. Invest. 52: 161, 1973.
21)
Shefer S, Hauser S, Mcsbach EH. Simulation of cholesterol 7a-hydroxylase by phenobarbital in two strains of rats. J. Lipid Res. 13: 69, 1972.
22)
Beitz J, Forster W. Influence of human low density and high density lipoprotein cholesterol on the in vitro PG12 Synthetase activity. Biochem. Biophys. Acta. 620: 352, 1980.
274
23)
24)
Ku EC, McPherson SE, Signor C, Chertock H, Cash WD. Characterization of imidazo [1,5-a] pyridine-5-hexanoic acid (CGS 13080) as a selective thromboxane synthetase inhibitor using in vitro and in vivo biochemical models. Biochem. Biophys. Res. Comm. 112: 899, 1983. Needleman P, Wyche A, Raz A. Platelet and blood vessel arachidonate metabolism and interactions. J. Clin. Invest. 63: 345, 1979.
275
PROST
C
(1987) 28. 267-275
Stimulation of Prostacyclin Synthesis in Rats Treated with Phenobarbital Ali 2. Haghighi and Thomas I. Pynadath Department of Chemistry, Kent State University Kent, Ohio 44242 (reprint requests to TIP) ABSTRACT The effect of phenobarbital treatment on the synthesis of prostacyclin in coronary vascular microsomes was studied in Sprague Dawley rats. It was found that the treatment increased the synthesis of prostacyclin by nearly 100%. The treatment also resulted in an increase in HDL and a decrease in LDL in the serum. In vitro effects of HDL and LDL on the microsomal synthesis of prostacyclin showed that the synthesis was stimulated by HDL and,inhibited by LDL. Hence it appears that the increase in prostacyclin synthesis resulting from phenobarbital treatment was at least partly due to increased level of HDL and decreased level of LDL in the serum. INTRODUCTION Prostacyclin (PSI 1, synthesized in the endothelial cells of the arteries & the prostacyclin synthetase enzyme system, has been shown to inhibit the aggregation of the platelets in the blood (1). Experimental atherosclerosis has been shown to be associated with a suppression of the synthesis of prostacyclin in the coronary vascular bed (2). Studies in vitro have shown that physiological concentrations of low density lipoprotein (LDL) inhibited the synthesis of PGI2 in pig arotic microsomes while similar concentrations of high density lipoprotein (HDL) stimulated the synthesisof pG12 (3). Thus, relative levels of LDL and HDL in the blood seem to have a considerable effect on the synthesis of prostacyclin in the endothelial cells. Hence it is likely that factors that would affect the levels of LDL and HDL in the blood will have a marked
267
effect on the synthesis prostacyclin. Phenobarbital has been shawn to increase the serum levels of HDL in both humans and rats (4,5). Hence this study was undertaken to determine the effect of phenobarbital treatment on the synthesis of prostacyclin. MATERIALS AND METHODS Spwye_lf awley rats were obtained from the Holtzman Company. C-arachidonic acid was purchased from the New England Nuclear Corporation, and authentic 6-keto-PGFl, was obtained from the Sigma Chemical Company. %enty three month old Sprague Dawley rats, weighing approximately 300 g, were divided into two equal groups and fed Laboratory Purina Rat Chow and water ad libitum. The experimental group was given daily intraperetonial injections of sodium phenobarbital (6 mg/lOO g body weight) in saline solution, for two days, while the control group received placebo injections of the saline solution. ar mlcrosomes. Vascular microsomes were prepared from the heart tissue. Rats from both groups were sacrificed 24 hours after the last injection of phenobarbital or saline solution and the heart tissue was collected from each animal and homogenized in 10 ml volume of oxygenated Kreb's buffer. The homogenates were then centrifuged at 700 x g for 10 min to sediment the nuclei and the debris. The supernatant was further centrifuged at 31,000 x g for 30 min to remove the mitochondria and most of the lysosomes. The supernatant containing mostly the microsomes was used as the enzyme preparation for the incubations. Protein was assayed by the Lowry method (6). . The assay of PGI synthesis was o the method of De inska-Kiec et al (2), by measuring the incorporation of l-rniC-arachidonic acid into 6-keto-PGFlu, the stable decomposition product of PGI2, when the labeled acid was incubated with the microsomal preparation. The incubation mixture contained 5 f microsomal protein and 35.2 nmole (0.06 UC) of ;"laC-arachidonic acid in Kreb's buffer, in a total volume of 2.1 ml. The incubation was carried out for 30 min at 37'C and the reaction was terminated by adjusting the pH to 3.0 by adding 0.5 M HCl. The contents were then passed three times through 3.0 g of XAD-2 amberlite resin packed in a narrow glass column to get all the acidic lipids including the 6-keto-PGFl, adsorbed on the resin (7). After washing off all the unadsorbed contaminants with
268
distilled water, the adsorbed lipids were eluted from the column with four 3-ml volumes of methanol. The pooled methanol extract was evaporated to dryness under a stream of nitrogen and the residue obtained was redissolved in 0.2 ml volume of chloroform-methanol (2:1, v/v). The prostaglandins in the residue were then separated by thin layer chromatography using Silica Gel 60F thin layer plates, using an ethyl acetate/iso-octane/acetic acid/water (11:5:2:1O,v/v) solvent system (8). The radioactive 6-keto-FGFl, spot, identified by cochromatography with non-radioactive authentic 6-Keto-FGF ci,was cut out from the chromatogram and its radioactivi4 determined using a liquid scintillation counter. Statistical analysis of the data was carried out by Student's t-test and results were expressed as mean $_ standard error of the mean (S.E.M.) RESULTS ect of_&&noba&,&&J on pI;I-svnthe is pGI2 synthesis by the coronary vascular microEomes of'th;!control and phenobarbital-treated rats are shown in Table 1. Phenobarbital treatment resulted in a marked increase in the synthesis of FG12 in the microsomes. The increase in the PG12 synthesis resulting from two days of phenobarbital treatment was nearly 100%. Table 1 Effect of phenobarbital treatment on PG12 synthesis by coronary vascular microsomes.
Animals Control (n = 13) 63.9 + 8.1
PB-treated
ect of -1 twnt on wum llnoorotejg_s. Serum lipoprotein composition was determined
269
semi-quantitatively by separating the lipoproteins of the serum, prestained with Sudan Black, by polyacrylamide disc electrophoresis and then scanning the gel at 610 nm in an autointegrating densitometer (9). The results are shcwn in Table 2. Phenobarbital treatment resulted in a significant increase in HDL and decrease in LDL. The HDL increase was nearly 16% while the LDL decrease was more than 30%. No significant change was observed in the VLDL fraction. Table 2 Effect of phenobarbital treatment on serum lipoproteins.
.
Animal group VLDL
ln comnosition (%) HDL LDL
Control
15 + 6 (n = 10)
20 &-4 (n = 10)
65 5 7 (n,= 10)
PB-treated
10 + 6 (n = 9)
14 * 4 (n = 10)
76 k 8 (n = 10)
(p
Addition
Amount added (mg/ml)
PGI synthesis (pmole3mg prot./30 min)
None LDL
HDL
1269 + 157 0.5 1.0 1.5 2.0
1091 939 786 660
+ 140 * 107 it 98 + 92
0.25 0.50 0.75 1.00
1446 1675 1776 1992
+ + + +
(p
270
132 148 145 151
of LDL and HDL on &I- Svnthpai The in vitro effect of LDL and HbL on the synthesis of PSI2 is shown in Table 3. The effect was determined as described by Beitz et al (3) at four different concentrations of each LDL and HDL. The amount of HDL or LDL added was measured in terms of the cholesterol content of the lipoproteins. LDL had a significant inhibitory effect on the PSI synthesis. At the highest concentration of the LDL studie2, the synthesis was inhibited by about 40%. The difference in the degree of the inhibition between two consecutive concentrations was statistically significant (P
271
not known at the present time. One probability is that phenobarbital is involved in the induction of one OK more enzymes involved in the synthesis of prostacyclin. It is well established that phenobabital induces the synthesis of proteins and enzymes in many tissues, especially the liver (16-21). Another probability is that the observed effect of phenobarbital on PGI synthesis is an indirect one. Previous studies have s8 own that phenobarbital treatment increases the HDL level and decreases the LDL level in the serum (4,s). The data of the present study has confirmed these findings. It has shown further that HDL stimulates the synthesis of PGI while LDL inhibits the synthesis. Beitz and Forster (23) have already demonstrated that HDL has a stimulatory effect on the synthesis of PGI in the vascular microsomes of pig. Hence, it appears t at the stimulation of PGI synthesis resulting from the phenobarbital trea8ment was at least partly due to the effect of the increased level of HDL in the serum.
2
Still another explanation for the observed stimulation of EG12 synthesis is the one suggested by Ku et al (2) and Needleman et al (24). These investigators observed that some of the dKUgS they studied stimulated the synthesis of prostacyclin while inhibiting the synthesis of thromboxane. They suggested that this was due to a drug induced shift in the metabolism of PGH2 in the system in such a way that it stimulated the synthesis of prostacyclin from PGH2 at the expense of the synthesis of thromboxane. Phenobarbital which stimulates prostacyclin synthesis and inhibits thromboxane synthesis (15) may be operating in a similar manner. Whatever the mechanism is, phenobarbital appears to have antithrombotic properties since it stimulates prostacyclin synthesis. In addition, it may also have antiatherogenic activity since it increases blood HDL level.. ACKNOWLEDGEMENT The authors thank Dr. Frederick Walz for his generous gift of phenobarbital. REFERENCES 1.
Moncada S, Grylewski R, Bunting S, Vane JR. An enzyme isolated from arteries transformed prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation, Nature 263: 663, 1976.
272
2.
Dembinska-Kiec A, Gryglewska T, Zmuda A, Gryglewski RI. The generation of prostacyclin by the coronary vascular bed is reduced in experimental atherosclerosis in rabbits. Prostaglandins 14: 1025, 1977.
3.
Beitz J, Forster W, Influence of human low density and high density lipoprotein cholesterol on the in vitro prostaglandin I2 synthetase activity. Biochim. Biophys. Acta 620: 352, 1980.
4.
Durrington PN. Effect of phenobarbital on plasma high-density-lipoprotein cholesterol in normal subjects, Clinical Science 56: 501, 1979.
5.
Chao YS, Pickett CB, Yamin TT, Alberts AW, Kroon PA. Phenobarbital induces rat liver apolipoprotein A-I 1985. mRNA. Molecular Pharmacology 27: 394,
6.
Lowry Oliver H, Rosebrough Nira J, Farr Lewis A, Randall Rose J. Protein measurement with the folin phenol reagent. J. Biol. Chem. 193: 265, 1951.
7.
Keirse M, Turnbull A. Extraction of prostaglandins from human blood. Prostaglandins 4: 607, 1973.
8.
Cottee F, Flower RJ, Flower JA, Vane JR. Synthesis of by ram seminal vesicle microsomes. 6-keto-PGF Prostaglanhins 14: 413, 1977.
9.
Naito KM, Wada M, Ehrhart LA, Lewis LA. Polyacrylamide gel disc electrophoresis as a screening procedure for serum lipoprotein abnormalities. Clin. Chem. 19: 228, 1973.
10.
Duguid JB. Thrombosis as a factor in the pathogenesis of aortic atherosclerosis. J. Path. Bact. 60: 57, 1948.
11.
Hand RA, Chandler AB. Atherosclerotic metamorphosis of autologous pulmonary thromboemboli in the rabbit. Am. J. Path. 40: 469, 1962.
12.
Woolf N, Bradley JW, Crawford T, Carstairs KC. Experimental mural thrombi in the pig aorta: The early natural history. Br. J. Exp. Pathol. 49: 257, 1968.
273
13.
Mitchell JR, Schwartz CJ. The relationship between myocardial lesions and coronary artery disease II: A selected group of patients with massive cardiac necrosis or scarring. Br. Heart J. 25: 111963.
14.
Moncada S, Vane JR. Pharmacology and endogenous roles of prostaglandin endoperoxides, thromboxane A2, and prostacycin. p. 293 in Pharmacological Reviews (PL Munson, ed) Williams and Wilkins Company, Baltimore, Maryland, 1978.
15.
Pynadath TI, Haghighi AZ. Inhibition of thromboxane A2 synthesis in rats treated with phenobarbital. Prostaglandins, Leukotrienes and Med. In press.
16.
Depierre JW, Seidegad J, Morgentern R, Balk L, Mesjer J, Astorm A. Induction of drug-metabolizing enzymes: a status report. p. 585 in Mitochondria and Microsomes (C Lee, G Schatz, G Dallner, eds.) Addison-Wesley Publishing Company, Reading, Massachusetts, 1981.
17)
Hilton J, Sartoreli AC. Induction by phenobarbital of microsomal mixed oxidase enzymes in regenrating rat liver. J. Biol. Chem. 245: 4187, 1970.
18)
Pfeil H, Bock KW. Electroimmunochemical qwtification of UDP-glucuronosyltransferase in rat liver microsomes. Eur. J. Biochem. 737: 619, 1983.
19)
Liu KD, and Owens GF. Phenobarbital enhances 2', 5'-oligoadenylate synthesis in rat liver nuclei. Biochem. Biophys. Res. Comm. 121: 788, 1984.
20)
Redinger RN and Smal DM. The effect of phenobarbital upon bile salt synthesis and pool size, biliary lipid secretion, and bile composition. J. Clin. Invest. 52: 161, 1973.
21)
Shefer S, Hauser S, Mcsbach EH. Simulation of cholesterol 7a-hydroxylase by phenobarbital in two strains of rats. J. Lipid Res. 13: 69, 1972.
22)
Beitz J, Forster W. Influence of human low density and high density lipoprotein cholesterol on the in vitro PG12 Synthetase activity. Biochem. Biophys. Acta. 620: 352, 1980.
274
23)
24)
Ku EC, McPherson SE, Signor C, Chertock H, Cash WD. Characterization of imidazo [1,5-a] pyridine-5-hexanoic acid (CGS 13080) as a selective thromboxane synthetase inhibitor using in vitro and in vivo biochemical models. Biochem. Biophys. Res. Comm. 112: 899, 1983. Needleman P, Wyche A, Raz A. Platelet and blood vessel arachidonate metabolism and interactions. J. Clin. Invest. 63: 345, 1979.
275
PROST
C