- Email: [email protected]
Effects of phenobarbital, chlordane, and oxytetracycline on DDT excretion in rats
ECOTOXICOLOGYANDENVIRONMENTALSAFETY~
2,261-266(1986)
Effects of Phenobarbital, Chlordane, and Oxytetracycline on DDT Excretion in Rats F. R. PUGA, M. A. LA R. RODRIGUES, AND M. DOKI Institute Biolbgico, Caixa Postal 7119,010OO. SZo Paula, Brazil Received May 12, I986 The effects of phenobarbital, chlordane, and oxytetracycline on DDT biliary excretion in rats were evaluated. The relationship between the increase of biliary flow induced by these drugs and the elimination of DDT was also evaluated. Phenobarbital (2.5 m&ml) was fed to rats in their drinking water and chlordane (200 mg/kg) was added to the diet over a period of 3 days; oxytetracycline (200 mg/kg/day) was fed to rats orally for 8 days. After these treatments [r4C]DDT was administered orally to anesthetized rats and then the bile was collected through cannulation of the bile duct. The data obtained show that (1) phenobarbital and chlordane decrease zoxaxolamine paralysis time and increase liver weight and biliary flow. Both drugs increase biliary excretion of [14C]DDT and decrease [14C]DDT levels in plasma; (2) oxytetracycline increases zoxazolamine flow significantly. Oxytetracycline does not change biliary excretion of [14C]DDT but decreases the blood levels of the insecticide; and (3) pretreatment of animals with phenobarbital, chlordane, and oxytetracycline does not significantly change [14C]DDT concentration in bile. These data demonstrate that the increased biliary excretion of DDT depends on the rate of bile elimination. Q 1986 Academic F’ress, Inc.
INTRODUCTION The metabolism and toxicity of insecticides might be affected by other foreign compounds. Since coexposure to many foreign chemicals is a common occurrence, it is desirable to examine the effects of commonly utilized drugs on the metabolism of insecticides. Phenobarbital and chlordane are potent hepatic enzyme inducers (Alary et al., 197 1; Conney et al., 1960; Conney, 1967; Kunz et al., 1966; Remmer, 1972). Phenobarbital increases the weight of rat liver (Conney et al., 1960), causes hypertrophy of the smooth endoplasmic reticulum in the hepatocytes (Staubli et al., 1969), and increases canalicular bile flow (Hart et al., 1969; Klaassen and Plaa, 1968; Roberts and Plaa, 1967). Considerable research has been directed toward determining the effect of antibiotics on microsomal activity (Adams, 1970, Adams and Sofia, 1973; Dixon and Fouts, 1962; Peters and Fouts, 1969; Tarara et al., 1976; Teske and Carter, 1971). Tarara et al. (1976) showed that oxytetracycline changes microsomal Odealkylation and epoxidation. The antibiotic has a biphasic effect on Odealkylation by exerting a dosedependent depression followed by an elevation in activity. Oxytetracycline decreases liver epoxidation; the mechanism of this inhibition is probably not competitive. The purposes of this investigation are (1) to compare the abilities of phenobarbital, chlordane, and oxytetracycline to change biliary flow, and (2) to determine the abilities of these chemicals to enhance plasma disappearance and biliary excretion of [ 14C]DDT. 261
0147-65 13/86 $3.00 Cotwigbt 8 1906 by Academic Press, Inc. All rigbt.9 of reprodwtioo in any form rc,served.
262
PUGA, RODRIGUES, AND DOIU TABLE 1
EFFECTS
OF PHENOBARBITAL, CHLORDANE, PARALYSIS TIME, LIVER WEIGHT,
Zoxazolamine paralysistime (min) Liver wet wt w MY M [14C]DDT concn in bile (dpm/mlp
AND OXYTETRACYCLINE ON ZOXAZOLAMINE AND [14C]DDT CONCENTRATION IN BILE
Chlordane
Oxytetracycline
Control
Phenobarbital
129f 13
29 +- 5*
6.94 f 0.11
8.46+0.16*
9.06 f 0.18*
1.32 -to.13
2922+388
30482390
3248+358
3233~~326
Note. Each value represents the mean + SE of 15 rats. pIBile was collected through 6-hr period after [?J]DDT * Significantly different from controls (P < 0.05).
MATERIAL
AND
34t-7*
141+ 18
administration.
METHODS
Animals. Wistar male rats (200 f 20 g), 120 f 15 days of age, were fed a commercial diet (Sgo Cristovgo, S%o Paulo) and water ad libitum. Chemicals. Chlordane was obtained from Biagro Velsicol, Sgo Paulo; DDT from Hoesch do Bras& Sso Paulo; phenobarbital and heparin from Fluka chemische, Switzerland, [ 14C]DDT from Radiochemical Centre Amersham, England; oxytetracycline from Squibb Chemical Industry, Sb Paulo; urethane from Riedel, West Germany; and zoxazolamine from Cilag, Switzerland. The stock solutions of chlordane (2 mg/ml) and DDT (20 mg/ml) were prepared in acetone; phenobarbital (2.5 mg/ ml) and oxytetracycline (200 mg/ml) were dissolved in water; heparin (100 UI/ml) and urethane (225 mg/ml) were dissolved in saline solution. Administration of phenobarbital, chlordane and oxytetracycline. For this experiment the rats were treated as follows. Group 1: The animals were fed with phenobarbital added to the drinking water (2.5 mg/ml) for 3 days. Group 2: The animals were fed with chlordane added to the chow (200 mg/kg) for 3 days. Group 3: The animals were treated with oxytetracycline administered orally (200 mg/kg/day) for 8 days. Group 4: The animals were untreated and served as controls. Zoxazolamineparalysis time. Rats treated with phenobarbital, chlordane, or oxytetracycline received zoxazolamine (60 mg/kg) ip and the duration of paralysis was measured. Paralysis time was defined as the time between loss and return of the righting reflex (Klaassen, 1969). Influence of phenobarbital, chlordane, and oxytetracycline on biliary jlow. Untreated rats and phenobarbital-, chlordane-, and oxytetracycline-treated rats were anesthetized with urethane (900 mg/kg) ip. The bile duct was exposed by a mid-line abdominal incision and cannulated with PE- 10 tubing. Alterations due to hypothermia were prevented by maintaining rectal temperature at 37°C with a heat-lamp temperature regulator device. Bile samples were collected at time intervals. At the end of 7 hr, the rats were killed by decapitation and the livers removed and weighed. Influence of phenobarbital, chlordane, and oxytetracycline on DDT blood concentration and biliary excretion. Phenobarbital-, chlordane-, and oxytetracycline-treated and untreated rats were anesthetized, had the bile ducts exposed as indicated above, and received orally administered [14C]DDT (40,000 dpm/ml) and DDT (4 mg/ml).
263
RATE OF DDT EXCRETION 5.0
I
4.0
? H
3.0
B f z >
2.0
1.0
1,
0
2
3
4
5
6
7
6
Fk. 1. Biliary flow of rats treated with phenobarbital, (2.5 mg/ml added to the drinking water for 3 days), chlordane (200 mg/kgadded to the chow for 3 days), and oxytetracycline (200 mg/kg/day administered orally for 8 days). Phenobarbital (---), chlordane (- . . -), oxytetracycline (-), control ( . . . ).
Blood and bile samples were collected at time intervals; heparin was added to all blood samples. The radioactivity was measured after addition of an aliquot to 10 ml of POP-POPOP scintillation liquid (New England Nuclear). Statistics. The data were compared by an analysis of variance. When the analysis indicated that a significant difference existed, the means of the treated groups were compared to the control mean by Tukey’s test. RESULTS
AND
DISCUSSION
The duration of action of most chemicals is determined by the speed at which they are metabolized and excreted. The rate of biotransformation of a large number of drugs is increased by agents that enhance microsomal enzyme activity. The data presented in Table 1 show that as has already been observed by other authors (Conney et al., 1960; Klaassen, 1969), zoxazolamine paralysis time is decreased by phenobarbital and chlordane but is increased by oxytetracycline. Phenobarbital, chlordane, aldrin, hexachlorcyclohexane, and other microsomal enzyme inducers exert an anabolic effect on liver that increases microsomal proteins
264
PUGA, RODRIGUES,
0
I
2
AND DOKI
4
3 Time
5
6
7
(hoursl
FIG. 2. [“‘CIDDT biliary excretion in rats pretreated with phenobarbital, chlordane, and oxytetracycline. Animals treated as indicated in Fig. 1 received orally administered [14C]DDT (40,000 dpm/ml). Bile samples were collected as indicated under Material and Methods. Phenobarbital (---), chlordane (-. . -), oxytetracycline (--), control (. . .).
and liver weight (Kunz et al., 1966). Our data show that phenobarbital and chlordane increase liver weight (Table 1) and bilk-y flow rate (Fig. 1). The increase in liver weight has been related to the enhancement of biliary flow by microsomal enzyme inducers (Fischer and Grecus, 1980; Hayes, 1965). For several reasons Klaassen ( 1974) suggested that the increase of biliary flow by phenobarbital and other microsomal enzyme inducers is probably not due simply to an increase in liver weight. First, the rates of increase in liver weight and biliary flow caused by phenobarbital did not parallel each other. Second, the increase in liver weight flow was higher than the increase in liver weight. Finally, the relative abilities of microsomal enzyme inducers to increase biliary flow and liver weight did not correlate. Pretreatment of the animals with phenobarbital and chlordane increases the biliary excretion of DDT (Fig. 2). This increase might result from the increase of biliary flow as no significant difference was observed on DDT concentration in the bile of animals treated either with phenobarbital, chlordane, or oxytetracycline as compared with control (Table 1). These data suggest that the biliary excretion of DDT depends on the rate of bile flow. Pretreatment of animals with phenobarbital, chlordane, and oxyteracycline decreases blood DDT concentration (Fig. 3). These data may be related to the increase of DDT bilk-y excretion rate caused by either phenobarbital or chlordane. Stiff and Castillo ( 1945) showed that blood DDT concentration is at maximum 2 hr after oral administration of DDT to rats. In our experiments the maximum of blood DDT concentration was observed between 4 and 6 hr of treatment. It might be that the
RATE OF DDT EXCRETION
265
2.00
I.30
2 3 % c! P H0 .c I,”
I.00
2
0.50
0.10 i 0 Timr
hours)
Frc. 3. [ 14C]DDT in plasma of rats pretreated with phenobarbital, chlordane, and oxy-tetracycline. Animals treated as indicated in Fig. 1 received orally administered [ 14C]DDT (40,000 dpm/ml). Blood samples were collected as indicated under Material and Methods. Phenobarbital (---), chlordane (-. . -), oxytetracycline (-), control (. . . ).
vegetable oil used to dissolve DDT could account for the discrepancy since it might facilitate DDT absorption through the intestinal mucosa. The decrease of blood DDT concentration after 6 hr of treatment might result from the storage of DDT in several organs. Lauger et al. (1945) showed that maximum DDT storage in animal organs occurs 2 to 5 hr after a single orally administered dose. The observation that oxytetracycline decreases blood DDT concentration but causes no change in the rate of DDT biliary excretion suggests that the antibiotic acts on the absorption and storage of DDT. Koransky et al. ( 1964) showed that the activation of microsomal enzymes in rats previously treated with phenobarbital is followed by an increase of urinary excretion of hexachlorcyclohexane metabolites. Alary et al. (197 1) observed that repeated administration of low doses of phenobarbital to dairy cows given DDT resulted in a significant decrease of total DDT metabolites in the milk. To explain this effect the authors suggested that despite an increased biotransformation of DDT upon the influence of the inducer, a slow and progressive buildup of the unmetabolized pesticide occurs in the adipose tissue. An alternative explanation is that phenobarbital initiates nonspecific mobilization of pesticide residues from the adipose tissue, either by displacement of the residues themselves or by some other unknown mechanisms.
266
PUGA, RODRIGUES,
AND DOKI
CONCLUSION This investigation shows that the rate of DDT excretion might be affected by interactions with other foreign chemicals. This observation indicates that a better understanding of these interactions might permit the development of effective therapeutic methods of increasing drug elimination. REFERENCES ADAMS, H. R. (1970). Prolongation of barbiturate anesthesia by chloramphenicol in laboratory animals. J. Amer. Vet. Med. Assoc. 157, 1908- 19 13. ADAMS, H. R., AND SOFIA, R. D. (1973). Interactions of chloramphenicol and tetrahydrocannabinol in barbital anesthetized mice. Experientia 29, 18 l-1 82. ALARY, J.-G., GUAY, P., AND BRODEUR, J. (197 1). Effect of phenobarbital pretreatment on the metabolism of DDT in the rat and the bovine. ToxicoZ. Appl. Pharmacol. l&457-468. CONNEY, A. H. (1967). Pharmacological implications of microsomal enzyme induction. Pharmacol. Rev. 19,317-366.
CONNEY, A. H., DAVISON, C., GASTER, R., AND BURNS, J. J. (1960). Adaptive increases in drug-metabolizing enzymes induced by phenobarbital and other drugs. J. Pharmacol. Exp. Ther. 130,1-8. DIXON, R. L., AND Fours, J. R. (1962). Inhibition of microsomal drug metabolic pathway by chloramphenicol. Biochem. Pharmacol. 11,715-720. FISCHER, E., AND GRFXUS, Z. (1980). Development and regression of the hepatic microsomal enzyme induction and stimulation of biliary excretion produced by phenobarbital in rats. Arch. Int. Pharmacodyn. 247,190-197.
HART, L. G., GUARINO, A. M., AND ADAMSON, R. H. (1969). Effects of phenobarbital on biliary excretion of organic acids in male and female rats. Amer. 1. Physiol. 217,46-52. HAYES, W. J., JR, (1965). Review of the metabolism of chlorinated hydrocarbon insecticides especially in mammals. Annu. Rev. Pharmacol. 5,27-52. KLAASSEN, C. D. (1969). Biliary flow after microsomal enzyme induction. J. Pharmacol. Exp. Ther. 188, 218-223. KLAASSEN, C. D. (1974). Effect of microsomal enzyme inducers on the biliary excretion of cardiac glycosides. J. Pharmacol. Exp. Ther. 191,201-2 11. KLAASSEN, C. D., AND PLAA, G. L. ( 1968). Studies on the mechanism of phenobarbital-enhanced sulfobromophthalein disappearance. J. Pharmacol. Exp. Ther. 61,361-366. KORANSKY, W., PORTIG, J., VOHLAND, H. W., AND KLEMPAU, I. (1964). Die Elimination von (Y-und flhexachlorcyclohexan und ihre Beeinflussung durch Enzyme der Lebermikrosomen. Arch. Exp. Pathol. Pharmakol.
247,49-60.
KUNZ, W., SCHAUDE, G., SCHMID, W., UND SIESS, M. (1966). Lebverergroszerung durch Fremdstoffe. Arch. Pharmakol.
Exp. Pathol.
254,470-488.
LAUGER, P., PULVER, R., AND MONTIGEL, C. (1945). Uber die Wirkungsweise von 4,4dichlordiphenyltrichlor-methylmethan (DDT-Geigy) im Wannbluter Organismus. He/v. Physiol. Pharmacol. Acta 3, 405-415. PETERS, M. A., AND FOUTS, J. R. (1969). The inhibitory effect of aureomycin (chlortetracycline) pretreatment on some rat liver microsomal enzyme activities. Biochem. Pharmacol, 18, 15 11. REMMER, H. (1972). Induction of drug metabolizing enzyme system in the liver. Eur. J. Clin. Pharmacol. 5,116-136. ROBERTS, R. J., AND PLAA, G. L. (1967). Effect ofphenobarbital on the excretion of an exogenous bilirukin load. Biochem. Pharmacol. 16,827-835. STAUBLI, W., HESS, R., AND WEIBEL, E. R. (1969). Correlated morphometric and biochemical studies on the liver cell. II. Effects of phenobarbital on rat hepatocytes. J. Cell. Biol. 42,92-l 12. STIFF, H. A., JR., AND CASTILLO, J. C. (1945). The determination of 2,2-bis-(n-chlorophenyl) l,l, I-trichlomethane (DDT) in organ body fluids after oral administration. J. Biol. Chem. 159,545-548. TARARA, R. P., HANSEN, L. G., AND SIMON, J. (1976). Effects of repeated administration of oxytetracychne on kidney, liver and liver mixed-function oxidases in the rat. Toxicol. Appl. Pharmacol. 35, 32 l332.
TESKE, R. H., AND CARTER, G. C. (197 1). Effect of chloramphenicol in dogs. Amer. Vet. Med. Assoc. 159,777-789.
on pentobarbital-induced
anesthesia
2,261-266(1986)
Effects of Phenobarbital, Chlordane, and Oxytetracycline on DDT Excretion in Rats F. R. PUGA, M. A. LA R. RODRIGUES, AND M. DOKI Institute Biolbgico, Caixa Postal 7119,010OO. SZo Paula, Brazil Received May 12, I986 The effects of phenobarbital, chlordane, and oxytetracycline on DDT biliary excretion in rats were evaluated. The relationship between the increase of biliary flow induced by these drugs and the elimination of DDT was also evaluated. Phenobarbital (2.5 m&ml) was fed to rats in their drinking water and chlordane (200 mg/kg) was added to the diet over a period of 3 days; oxytetracycline (200 mg/kg/day) was fed to rats orally for 8 days. After these treatments [r4C]DDT was administered orally to anesthetized rats and then the bile was collected through cannulation of the bile duct. The data obtained show that (1) phenobarbital and chlordane decrease zoxaxolamine paralysis time and increase liver weight and biliary flow. Both drugs increase biliary excretion of [14C]DDT and decrease [14C]DDT levels in plasma; (2) oxytetracycline increases zoxazolamine flow significantly. Oxytetracycline does not change biliary excretion of [14C]DDT but decreases the blood levels of the insecticide; and (3) pretreatment of animals with phenobarbital, chlordane, and oxytetracycline does not significantly change [14C]DDT concentration in bile. These data demonstrate that the increased biliary excretion of DDT depends on the rate of bile elimination. Q 1986 Academic F’ress, Inc.
INTRODUCTION The metabolism and toxicity of insecticides might be affected by other foreign compounds. Since coexposure to many foreign chemicals is a common occurrence, it is desirable to examine the effects of commonly utilized drugs on the metabolism of insecticides. Phenobarbital and chlordane are potent hepatic enzyme inducers (Alary et al., 197 1; Conney et al., 1960; Conney, 1967; Kunz et al., 1966; Remmer, 1972). Phenobarbital increases the weight of rat liver (Conney et al., 1960), causes hypertrophy of the smooth endoplasmic reticulum in the hepatocytes (Staubli et al., 1969), and increases canalicular bile flow (Hart et al., 1969; Klaassen and Plaa, 1968; Roberts and Plaa, 1967). Considerable research has been directed toward determining the effect of antibiotics on microsomal activity (Adams, 1970, Adams and Sofia, 1973; Dixon and Fouts, 1962; Peters and Fouts, 1969; Tarara et al., 1976; Teske and Carter, 1971). Tarara et al. (1976) showed that oxytetracycline changes microsomal Odealkylation and epoxidation. The antibiotic has a biphasic effect on Odealkylation by exerting a dosedependent depression followed by an elevation in activity. Oxytetracycline decreases liver epoxidation; the mechanism of this inhibition is probably not competitive. The purposes of this investigation are (1) to compare the abilities of phenobarbital, chlordane, and oxytetracycline to change biliary flow, and (2) to determine the abilities of these chemicals to enhance plasma disappearance and biliary excretion of [ 14C]DDT. 261
0147-65 13/86 $3.00 Cotwigbt 8 1906 by Academic Press, Inc. All rigbt.9 of reprodwtioo in any form rc,served.
262
PUGA, RODRIGUES, AND DOIU TABLE 1
EFFECTS
OF PHENOBARBITAL, CHLORDANE, PARALYSIS TIME, LIVER WEIGHT,
Zoxazolamine paralysistime (min) Liver wet wt w MY M [14C]DDT concn in bile (dpm/mlp
AND OXYTETRACYCLINE ON ZOXAZOLAMINE AND [14C]DDT CONCENTRATION IN BILE
Chlordane
Oxytetracycline
Control
Phenobarbital
129f 13
29 +- 5*
6.94 f 0.11
8.46+0.16*
9.06 f 0.18*
1.32 -to.13
2922+388
30482390
3248+358
3233~~326
Note. Each value represents the mean + SE of 15 rats. pIBile was collected through 6-hr period after [?J]DDT * Significantly different from controls (P < 0.05).
MATERIAL
AND
34t-7*
141+ 18
administration.
METHODS
Animals. Wistar male rats (200 f 20 g), 120 f 15 days of age, were fed a commercial diet (Sgo Cristovgo, S%o Paulo) and water ad libitum. Chemicals. Chlordane was obtained from Biagro Velsicol, Sgo Paulo; DDT from Hoesch do Bras& Sso Paulo; phenobarbital and heparin from Fluka chemische, Switzerland, [ 14C]DDT from Radiochemical Centre Amersham, England; oxytetracycline from Squibb Chemical Industry, Sb Paulo; urethane from Riedel, West Germany; and zoxazolamine from Cilag, Switzerland. The stock solutions of chlordane (2 mg/ml) and DDT (20 mg/ml) were prepared in acetone; phenobarbital (2.5 mg/ ml) and oxytetracycline (200 mg/ml) were dissolved in water; heparin (100 UI/ml) and urethane (225 mg/ml) were dissolved in saline solution. Administration of phenobarbital, chlordane and oxytetracycline. For this experiment the rats were treated as follows. Group 1: The animals were fed with phenobarbital added to the drinking water (2.5 mg/ml) for 3 days. Group 2: The animals were fed with chlordane added to the chow (200 mg/kg) for 3 days. Group 3: The animals were treated with oxytetracycline administered orally (200 mg/kg/day) for 8 days. Group 4: The animals were untreated and served as controls. Zoxazolamineparalysis time. Rats treated with phenobarbital, chlordane, or oxytetracycline received zoxazolamine (60 mg/kg) ip and the duration of paralysis was measured. Paralysis time was defined as the time between loss and return of the righting reflex (Klaassen, 1969). Influence of phenobarbital, chlordane, and oxytetracycline on biliary jlow. Untreated rats and phenobarbital-, chlordane-, and oxytetracycline-treated rats were anesthetized with urethane (900 mg/kg) ip. The bile duct was exposed by a mid-line abdominal incision and cannulated with PE- 10 tubing. Alterations due to hypothermia were prevented by maintaining rectal temperature at 37°C with a heat-lamp temperature regulator device. Bile samples were collected at time intervals. At the end of 7 hr, the rats were killed by decapitation and the livers removed and weighed. Influence of phenobarbital, chlordane, and oxytetracycline on DDT blood concentration and biliary excretion. Phenobarbital-, chlordane-, and oxytetracycline-treated and untreated rats were anesthetized, had the bile ducts exposed as indicated above, and received orally administered [14C]DDT (40,000 dpm/ml) and DDT (4 mg/ml).
263
RATE OF DDT EXCRETION 5.0
I
4.0
? H
3.0
B f z >
2.0
1.0
1,
0
2
3
4
5
6
7
6
Fk. 1. Biliary flow of rats treated with phenobarbital, (2.5 mg/ml added to the drinking water for 3 days), chlordane (200 mg/kgadded to the chow for 3 days), and oxytetracycline (200 mg/kg/day administered orally for 8 days). Phenobarbital (---), chlordane (- . . -), oxytetracycline (-), control ( . . . ).
Blood and bile samples were collected at time intervals; heparin was added to all blood samples. The radioactivity was measured after addition of an aliquot to 10 ml of POP-POPOP scintillation liquid (New England Nuclear). Statistics. The data were compared by an analysis of variance. When the analysis indicated that a significant difference existed, the means of the treated groups were compared to the control mean by Tukey’s test. RESULTS
AND
DISCUSSION
The duration of action of most chemicals is determined by the speed at which they are metabolized and excreted. The rate of biotransformation of a large number of drugs is increased by agents that enhance microsomal enzyme activity. The data presented in Table 1 show that as has already been observed by other authors (Conney et al., 1960; Klaassen, 1969), zoxazolamine paralysis time is decreased by phenobarbital and chlordane but is increased by oxytetracycline. Phenobarbital, chlordane, aldrin, hexachlorcyclohexane, and other microsomal enzyme inducers exert an anabolic effect on liver that increases microsomal proteins
264
PUGA, RODRIGUES,
0
I
2
AND DOKI
4
3 Time
5
6
7
(hoursl
FIG. 2. [“‘CIDDT biliary excretion in rats pretreated with phenobarbital, chlordane, and oxytetracycline. Animals treated as indicated in Fig. 1 received orally administered [14C]DDT (40,000 dpm/ml). Bile samples were collected as indicated under Material and Methods. Phenobarbital (---), chlordane (-. . -), oxytetracycline (--), control (. . .).
and liver weight (Kunz et al., 1966). Our data show that phenobarbital and chlordane increase liver weight (Table 1) and bilk-y flow rate (Fig. 1). The increase in liver weight has been related to the enhancement of biliary flow by microsomal enzyme inducers (Fischer and Grecus, 1980; Hayes, 1965). For several reasons Klaassen ( 1974) suggested that the increase of biliary flow by phenobarbital and other microsomal enzyme inducers is probably not due simply to an increase in liver weight. First, the rates of increase in liver weight and biliary flow caused by phenobarbital did not parallel each other. Second, the increase in liver weight flow was higher than the increase in liver weight. Finally, the relative abilities of microsomal enzyme inducers to increase biliary flow and liver weight did not correlate. Pretreatment of the animals with phenobarbital and chlordane increases the biliary excretion of DDT (Fig. 2). This increase might result from the increase of biliary flow as no significant difference was observed on DDT concentration in the bile of animals treated either with phenobarbital, chlordane, or oxytetracycline as compared with control (Table 1). These data suggest that the biliary excretion of DDT depends on the rate of bile flow. Pretreatment of animals with phenobarbital, chlordane, and oxyteracycline decreases blood DDT concentration (Fig. 3). These data may be related to the increase of DDT bilk-y excretion rate caused by either phenobarbital or chlordane. Stiff and Castillo ( 1945) showed that blood DDT concentration is at maximum 2 hr after oral administration of DDT to rats. In our experiments the maximum of blood DDT concentration was observed between 4 and 6 hr of treatment. It might be that the
RATE OF DDT EXCRETION
265
2.00
I.30
2 3 % c! P H0 .c I,”
I.00
2
0.50
0.10 i 0 Timr
hours)
Frc. 3. [ 14C]DDT in plasma of rats pretreated with phenobarbital, chlordane, and oxy-tetracycline. Animals treated as indicated in Fig. 1 received orally administered [ 14C]DDT (40,000 dpm/ml). Blood samples were collected as indicated under Material and Methods. Phenobarbital (---), chlordane (-. . -), oxytetracycline (-), control (. . . ).
vegetable oil used to dissolve DDT could account for the discrepancy since it might facilitate DDT absorption through the intestinal mucosa. The decrease of blood DDT concentration after 6 hr of treatment might result from the storage of DDT in several organs. Lauger et al. (1945) showed that maximum DDT storage in animal organs occurs 2 to 5 hr after a single orally administered dose. The observation that oxytetracycline decreases blood DDT concentration but causes no change in the rate of DDT biliary excretion suggests that the antibiotic acts on the absorption and storage of DDT. Koransky et al. ( 1964) showed that the activation of microsomal enzymes in rats previously treated with phenobarbital is followed by an increase of urinary excretion of hexachlorcyclohexane metabolites. Alary et al. (197 1) observed that repeated administration of low doses of phenobarbital to dairy cows given DDT resulted in a significant decrease of total DDT metabolites in the milk. To explain this effect the authors suggested that despite an increased biotransformation of DDT upon the influence of the inducer, a slow and progressive buildup of the unmetabolized pesticide occurs in the adipose tissue. An alternative explanation is that phenobarbital initiates nonspecific mobilization of pesticide residues from the adipose tissue, either by displacement of the residues themselves or by some other unknown mechanisms.
266
PUGA, RODRIGUES,
AND DOKI
CONCLUSION This investigation shows that the rate of DDT excretion might be affected by interactions with other foreign chemicals. This observation indicates that a better understanding of these interactions might permit the development of effective therapeutic methods of increasing drug elimination. REFERENCES ADAMS, H. R. (1970). Prolongation of barbiturate anesthesia by chloramphenicol in laboratory animals. J. Amer. Vet. Med. Assoc. 157, 1908- 19 13. ADAMS, H. R., AND SOFIA, R. D. (1973). Interactions of chloramphenicol and tetrahydrocannabinol in barbital anesthetized mice. Experientia 29, 18 l-1 82. ALARY, J.-G., GUAY, P., AND BRODEUR, J. (197 1). Effect of phenobarbital pretreatment on the metabolism of DDT in the rat and the bovine. ToxicoZ. Appl. Pharmacol. l&457-468. CONNEY, A. H. (1967). Pharmacological implications of microsomal enzyme induction. Pharmacol. Rev. 19,317-366.
CONNEY, A. H., DAVISON, C., GASTER, R., AND BURNS, J. J. (1960). Adaptive increases in drug-metabolizing enzymes induced by phenobarbital and other drugs. J. Pharmacol. Exp. Ther. 130,1-8. DIXON, R. L., AND Fours, J. R. (1962). Inhibition of microsomal drug metabolic pathway by chloramphenicol. Biochem. Pharmacol. 11,715-720. FISCHER, E., AND GRFXUS, Z. (1980). Development and regression of the hepatic microsomal enzyme induction and stimulation of biliary excretion produced by phenobarbital in rats. Arch. Int. Pharmacodyn. 247,190-197.
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anesthesia