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Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Effect of chronic exposure to cadmium on hepatic drug metabolism a
R. R. Dalvi & T. J. Robbins
a
a
Toxicology Laboratory, Department of Physiology and Pharmacology,School of Veterinary Medicine , Tuskegee Institute , Alabama, 36088, U.S.A. Published online: 14 Nov 2008.
To cite this article: R. R. Dalvi & T. J. Robbins (1979) Effect of chronic exposure to cadmium on hepatic drug metabolism, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 14:6, 603-615, DOI: 10.1080/03601237909372154 To link to this article: http://dx.doi.org/10.1080/03601237909372154
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions
and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [Universite Laval] at 04:13 05 March 2015
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
J. ENVIRON. SCI. HEALTH, B14(6), 603-615 (1979)
EFFECT OF CHRONIC EXPOSURE TO CADMIUM ON HEPATIC DRUG METABOLISM
Downloaded by [Universite Laval] at 04:13 05 March 2015
KEY WORDS:
Cadmium, microsomes, biotransformation, drug-metabolizing enzyme system, cytochrome P-450
R. R. Dalvi and T. J. Robbins Toxicology Laboratory Department of Physiology and Pharmacology School of Veterinary Medicine Tuskegee Institute, Alabama 36088, U.S.A. ABSTRACT In an attempt to examine the chronic effect of low levels of cadmium on hepatic drug-metabolizing enzyme system, an experiment was carried out in which growing
male rats were given 0, 5, 10, and 2 0 ppm of cadmium in drinking water for a period of 8 weeks.
An ip adminis-
tration of a hypnotic dose of pentobarbital to the cadmium-treated and the control rats 2 4 hr following
the termination of the experiment exhibited that there
was no significant difference in the drug metabolism in control and any of the treated groups.
Next, liver
microsomes were isolated from animals in all groups to study their ability to metabolize drugs in vitro.
The
603 Copyright alteration m
microsomal enzyme activity ,
poor bone mineralization
, and even in teratogenic
malformations and carcinogenesis1. Relatively little work concerning chronic effects
of cadmium in experimental animals exposed to very low levels has been reported. added to drinking water
At a 5 ppm level of cadmium of rats or mice resulted in
high tumor incidence, shortened life span, damage to liver, kidney and heart, and neurological disorders 19
'
'
• On the other hand, dietary levels of cadmium up to
3 0 ppm fed to rats over a period of 3 months did not
cause any blood, liver or kidney damage ,
However,
both these studies did not include the cadmium effect on the hepatic drug-metabolizing enzyme system that is involved in the activation or deactivation of drugs and other foreign chemicals entering the body.
Although
numerous reports have demonstrated that a single ip subacute dose of cadmium resulted in the inhibition of drug-metabolizing enzymes-"-15 t studies on the effect
606
DALVI AND ROBBINS
of chronic low levels of cadmium on this important enzyme system are needed. Interestingly, a study by g Wagstaff demonstrated stimulation of drug-metabolizing enzymes in rats fed dietary cadmium (500-5000 ppm) over a period of 15 days.
The present work was carried out
to determine the effect on the rat liver microsomal Downloaded by [Universite Laval] at 04:13 05 March 2015
enzymes of low levels of cadmium (0-20 ppm) in drinking water over a period of 8 weeks. MATERIALS AND METHODS Chemicals Glucose-6-phosphate, glucose-6-phosphate dehydrogenase, nicotinamide-adenine dinucleotide phosphate (NADP) (Boehringer and Mannheim Corp., New York), cadmium chloride (Aldrich Chemical Co., Milwaukee, Wis.) and pentobarbital (Sigma Chemical Co., St. Louis, Mo.) were purchased commercially.
Benzphetamine (The Upjohn
Co., Kalamazoo, Mich.) was obtained as a gift.
All
other chemicals were of reagent grade. Animal Treatment Male Sprague-Dawley rats weighing 90-110 g were divided into 4 groups each having at least 10 animals. The first group was taken as a control and received no cadmium in drinking water.
Each of the next three
groups was given cadmium (as cadmium chloride) in
CHRONIC EXPOSURE TO CADMIUM
607
drinking water at a level of 5, 10, and 20 ppm, respectively.
All groups of animals were maintained
for 8 weeks with access to feed (Purina chow) and water at all times except otherwise stated.
The drinking
water with or without cadmium was provided in glass bottles and changed daily.
The rats were housed in
Downloaded by [Universite Laval] at 04:13 05 March 2015
stainless steel cages (10 per cage) in a temperature-
and light-controlled room.
At the end of the 8-week
experimental period, rats were taken off the cadmium
treatment and 24 hr later pentobarbital sleeping time
was determined. Isolation and Incubation of Microsomes Rats were sacrificed by decapitation, livers were
removed, weighed and perfused immediately with cold 1.15% KC1 and homogenized in 0.25 M sucrose solution.
Hepatic microsomes were isolated as described previously-'-^ . Ability of microsomes isolated from the control
and cadmium-treated animals to metabolize benzphetamine to formaldehyde and aniline to p-aminophenol was examined by incubating the microsomes with benzphetamine or aniline in the presence of NADPH-generating system
.
The cytochrome P-M-5 0 content of the micro-
somes was determined by the procedure of Omura and Sato 1 7 .
608
DALVI AND ROBBINS Amount of protein in each sample was estimated
using biuret method modified to include deoxycholate in the samples-*- • RESULTS AND DISCUSSION
Downloaded by [Universite Laval] at 04:13 05 March 2015
The results presented in Table 1 are from an experiment in which rats with initial body weight in the range of 90-110 g were divided into five groups each containing 10 animals and exposed to 0, 5, 10, and 2 0 ppm of cadmium in drinking water for a period of 8 weeks.
As can be seen from Table 1, gain in body
weight of the treated animals did not significantly differ from that of the control group.
Further, in
order to assess the effect of cadmium treatment on the in vivo metabolism of pentobarbital, 5 rats from each group were given a hypnotic dose of pentobarbital (50 mg/kg, ip) 2>+ hr post-termination of the experiment and the duration of hypnosis was measured as the time elapsed between losing and regaining the righting reflex.
It is evident from the data (Table 1) that
chronic exposure to cadmium up to 2 0 ppm did not result in a significant change in the capacity of rat liver microsomal enzymes to metabolize pentobarbital. Simultaneously, remaining 5 animals from each group were sacrificed by decapitation and hepatic microsomes isolated to examine their ability to metabo-
TABLE 1
g
Downloaded by [Universite Laval] at 04:13 05 March 2015
M O
Effi o.. of Chronic Cadmium Treatment (8 weeks) on Body Weight Gain, Pentobarbital-Induced Hypnosis and Components of Microsomal DrugMetabolizing Enzyme System a Cadmium • in Initial Body Duration drinking body weight of water weight gair hypnosis (ppm) (g/rat) (g/rat) (min)
a
Hepatic microsomal enzymes Benzphetamine Aniline N-demethyhydroxyCytochrome laseb laseG P-450 d
0
97
247
52 + 8
4.12 +_ 0.33
0.37 +_ 0.01
0.82 +_ 0.03
5
94
258
57 +_ 5
4.73 +_ 0.29
0.41 + 0.0H
0.78 +_ 0.05
10
106
259
53 +_ 4
4.65 +_ 0.36
0.39 +_ 0.03
0.73 +_ 0.02
20
110
264
58 +_ 8
4.45 +_ 0.24
0.41 +_ 0.07
0.84 +_ 0.06
w
^ g g n
^ § §
Results are expressed as the mean of 5 determinations +_ S.E.M.
"nmoles formaldehyde formed/min/mg of microsomal protein c
nmoles p-aminophenol formed/min/mg of microsomal protein nmoles/mg of microsomal protein
CTv O
610
DALVI AND ROBBINS
lize benzphetamine as a type I substrate and aniline as a type II substrate in vitro.
An aliquot-from each
sample was also used to determine the cytochrome P-450 content.
The results (Table 1) indicate that there is
no appreciable difference in the rate of metabolism of benzphetamine or aniline by microsomal enzymes from the
Downloaded by [Universite Laval] at 04:13 05 March 2015
control and the treated rats.
Similarly, the various
levels of cadmium did not affect the amount of cytochrome P-i^O, the major component of the drug-metabolizing enzyme system.
Thus the data on the in vivo
metabolism of pentobarbital are in agreement with the in vitro metabolism of benzphetamine and aniline confirming the contention that animals chronically exposed to cadmium up to 2 0 ppm in drinking water over a period of 8 weeks do not show impairment in their ability to metabolize drugs or other foreign chemicals. During the course of the chronic experiment, it was observed that a rat weighing about 350 g had daily water intake of 30-40 ml.
Based on these observations,
it is calculated that rats on 20 ppm cadmium in drinking water received a daily oral dose of the metallic toxicant equivalent to approximately 2 mg/kg. Therefore, for the comparison, a single 2 mg/kg dose of cadmium was administered ip to a group of normal rats and its effect on hepatic drug metabolism was studied 7 2 hr following the treatment.
The results shown in
CHRONIC EXPOSURE TO CADMIUM
611
Table 2, demonstrate that the single 2 mg/kg ip dose of cadmium caused singificantly greater prolongation of pentobarbital sleeping time even at 72 hr after the treatment suggesting the inhibition of the microsomal enzymes by cadmium.
When liver microsomes isolated
from the control and the cadmium-treated animals incuDownloaded by [Universite Laval] at 04:13 05 March 2015
bated with benzphetamine or aniline a substantial loss
of the activity of benzphetamine N-demethylase and aniline hydroxylase was noted in the treated versus control animals.
Likewise, there was a considerable
loss of microsomal cytochrome P-450 in the treated animals. As previously reported by several workers 1 3 "^,
these data confirm that 2 mg/kg dose of cadmium given ip to rats causes significant inhibition of the microsomal biotrasformation enzymes.
However, an almost
equal daily dose of cadmium given orally does not cause inhibitory effect on the drug-metabolizing enzyme system.
This may be attributed to the fact that gastro-
intestinal absorption of cadmium could be poor due to the presence of feed in the stomach
.
It should also
be noted that the presence of other minerals in diet such as calcium can reduce the absorption of cadmium from the stomach^0.
Furthermore, in chronic experiment,
the total daily intake of cadmium was distributed over a period of 24 hr.
Therefore, it is possible that
Downloaded by [Universite Laval] at 04:13 05 March 2015
TABLE 2 Effect of a Single Dose of Cadmium (2 mg/kg, ip) on Pentobarbital-Induced Hypnosis and Components of Microsomal Drug-Metabolizing Enzyme Systema
Hepatic microsomal enzymes
Treatment
Duration of hypnosis (min)
Benzphetamine N-demethylaseb
Aniline hydroxylase0
Cytochrqme P-450
Control
67 +_ 7
3.89 + 0.40
0.21 + 0.09
0.77 +0.07
Cadmium
117 + 11
1.94 + 0.29
0.14 + 0.05
0.47 + 0.05
Results are expressed as the mean of 5 determinations + S.E.M. nmoles formaldehyde formed/min/mg of microsomal protein
I
"nmolen p-aminophenol. formed/min/ng of microsomal protein nmo] en/rng of microsomal protein
63 H 2!
CHRONIC EXPOSURE TO CADMIUM
613
enough concentration of absorbed cadmium would not be present at a given time in the liver to cause inhibition of microsomal enzymes.
As reported previously, chronic
exposure to cadmium results in the induction of cadmium binding protein known as metalloghionein 21 . This
Downloaded by [Universite Laval] at 04:13 05 March 2015
specific protein binding of cadmium may, in part, account for some protection of the microsomal enzymes. Thus, these studies indicate that chronic exposure to cadmium up to 2 0 ppm in drinking water over a period of 8 weeks is unlikely to affect hepatic drug metabolism.
REFERENCES 1.
Webb, M., Brit. Med. Bull., 31, 246-250 (1975)
2.
Exon, J. H. , J. G. Lamberton, and L. D. Koller, Bull. Environ. Contam. Toxicol., 18, 74-76 (1977)
3.
Flick, D. F., H. F. Kraybill, and J. M. Dimetroff, Environ. Res., 4, 71-85 (1971)
4.
Olwin, J. H., J. Anal. Toxicol., 1, 245-251 (1977)
5.
Schroeder, H. A., W. H. Vinton, and J. J. Balassa, J. Nutr., 80, 48-54 (1963)
6.
Powell, G. W., W. J. Miller, J. D. Morton; and C. M. Clifton, J. Nutr., 84, 205-214 (1964)
7.
Loeser, E. and D. Lorke, Toxicology, 7, 215-224 (1977)
614 8.
DALVI AND ROBBINS Diamond, E. M. and J. E. Kench, Environ. Physiol. Biochem., 4, 280-283 (1974)
9.
Wagstaff, D. D.,
Bull. Environ. Contam. Toxicol.,
10, 328-332 (1973) 10.
Hastings, L, H. Choudhary, H. G. Petering, and G. P. Cooper, Bull. Environ. Contam. Toxicol., 20,
Downloaded by [Universite Laval] at 04:13 05 March 2015
96-101 (1978) 11.
Schroeder, H. A., J. J. Balassa, and W. H. Vinton, J. Nutr., 83, 239-250 (1964)
12.
Schroeder, H. A., J. J. Balassa, and W. H. Vinton, J. Nutr., 86, 51-56 (1965)
13.
Hadley,
W. M., T. S. Miya, and W. F. Bousquet,
Toxicol. Appl. Pharmacol., 28, 284-291 (1974) 14.
Yoshida,
T. K., Y. Ito, and Y. Suzuki, Bull.
Environ. Contam. Toxicol., 15, 402-405 (1976) 15.
Dalvi,
R. R. and T. J. Robbins, J. Environ. Path.
Toxicol., 1, 601-607 (1978) 16.
Dalvi, R. R. and C. D. Howell, Bull. Environ. Contam. Toxicol., 17, 225-232 (1977)
17.
Omura, T. and R. Sato, J. Biol. Chem., 239, 23702378 (1964)
18.
Dalvi, R. R., A. L. Hunter, and R. A. Neal, Chem.Biol. Interactions, 10, 349-361 (1975)
19.
Kotsonis, F. N. and C. D. Klaassen, Toxicol. Appl. Pharmacol, 41, 667-680 (1977)
CHRONIC EXPOSURE TO CADMIUM
20.
615
Washko, P. W. and R. J . C o u s i n s , J . E n v i r o n . H e a l t h , 1 , 1055-1066
21.
Toxicol.
(1976)
S h a i k h , Z. A. and O. G. L u c i s , Fed. P r o c . , 2 9 ,
Downloaded by [Universite Laval] at 04:13 05 March 2015
298 (1970)
Received:
January 15, 1979.
Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Effect of chronic exposure to cadmium on hepatic drug metabolism a
R. R. Dalvi & T. J. Robbins
a
a
Toxicology Laboratory, Department of Physiology and Pharmacology,School of Veterinary Medicine , Tuskegee Institute , Alabama, 36088, U.S.A. Published online: 14 Nov 2008.
To cite this article: R. R. Dalvi & T. J. Robbins (1979) Effect of chronic exposure to cadmium on hepatic drug metabolism, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 14:6, 603-615, DOI: 10.1080/03601237909372154 To link to this article: http://dx.doi.org/10.1080/03601237909372154
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions
and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [Universite Laval] at 04:13 05 March 2015
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
J. ENVIRON. SCI. HEALTH, B14(6), 603-615 (1979)
EFFECT OF CHRONIC EXPOSURE TO CADMIUM ON HEPATIC DRUG METABOLISM
Downloaded by [Universite Laval] at 04:13 05 March 2015
KEY WORDS:
Cadmium, microsomes, biotransformation, drug-metabolizing enzyme system, cytochrome P-450
R. R. Dalvi and T. J. Robbins Toxicology Laboratory Department of Physiology and Pharmacology School of Veterinary Medicine Tuskegee Institute, Alabama 36088, U.S.A. ABSTRACT In an attempt to examine the chronic effect of low levels of cadmium on hepatic drug-metabolizing enzyme system, an experiment was carried out in which growing
male rats were given 0, 5, 10, and 2 0 ppm of cadmium in drinking water for a period of 8 weeks.
An ip adminis-
tration of a hypnotic dose of pentobarbital to the cadmium-treated and the control rats 2 4 hr following
the termination of the experiment exhibited that there
was no significant difference in the drug metabolism in control and any of the treated groups.
Next, liver
microsomes were isolated from animals in all groups to study their ability to metabolize drugs in vitro.
The
603 Copyright alteration m
microsomal enzyme activity ,
poor bone mineralization
, and even in teratogenic
malformations and carcinogenesis1. Relatively little work concerning chronic effects
of cadmium in experimental animals exposed to very low levels has been reported. added to drinking water
At a 5 ppm level of cadmium of rats or mice resulted in
high tumor incidence, shortened life span, damage to liver, kidney and heart, and neurological disorders 19
'
'
• On the other hand, dietary levels of cadmium up to
3 0 ppm fed to rats over a period of 3 months did not
cause any blood, liver or kidney damage ,
However,
both these studies did not include the cadmium effect on the hepatic drug-metabolizing enzyme system that is involved in the activation or deactivation of drugs and other foreign chemicals entering the body.
Although
numerous reports have demonstrated that a single ip subacute dose of cadmium resulted in the inhibition of drug-metabolizing enzymes-"-15 t studies on the effect
606
DALVI AND ROBBINS
of chronic low levels of cadmium on this important enzyme system are needed. Interestingly, a study by g Wagstaff demonstrated stimulation of drug-metabolizing enzymes in rats fed dietary cadmium (500-5000 ppm) over a period of 15 days.
The present work was carried out
to determine the effect on the rat liver microsomal Downloaded by [Universite Laval] at 04:13 05 March 2015
enzymes of low levels of cadmium (0-20 ppm) in drinking water over a period of 8 weeks. MATERIALS AND METHODS Chemicals Glucose-6-phosphate, glucose-6-phosphate dehydrogenase, nicotinamide-adenine dinucleotide phosphate (NADP) (Boehringer and Mannheim Corp., New York), cadmium chloride (Aldrich Chemical Co., Milwaukee, Wis.) and pentobarbital (Sigma Chemical Co., St. Louis, Mo.) were purchased commercially.
Benzphetamine (The Upjohn
Co., Kalamazoo, Mich.) was obtained as a gift.
All
other chemicals were of reagent grade. Animal Treatment Male Sprague-Dawley rats weighing 90-110 g were divided into 4 groups each having at least 10 animals. The first group was taken as a control and received no cadmium in drinking water.
Each of the next three
groups was given cadmium (as cadmium chloride) in
CHRONIC EXPOSURE TO CADMIUM
607
drinking water at a level of 5, 10, and 20 ppm, respectively.
All groups of animals were maintained
for 8 weeks with access to feed (Purina chow) and water at all times except otherwise stated.
The drinking
water with or without cadmium was provided in glass bottles and changed daily.
The rats were housed in
Downloaded by [Universite Laval] at 04:13 05 March 2015
stainless steel cages (10 per cage) in a temperature-
and light-controlled room.
At the end of the 8-week
experimental period, rats were taken off the cadmium
treatment and 24 hr later pentobarbital sleeping time
was determined. Isolation and Incubation of Microsomes Rats were sacrificed by decapitation, livers were
removed, weighed and perfused immediately with cold 1.15% KC1 and homogenized in 0.25 M sucrose solution.
Hepatic microsomes were isolated as described previously-'-^ . Ability of microsomes isolated from the control
and cadmium-treated animals to metabolize benzphetamine to formaldehyde and aniline to p-aminophenol was examined by incubating the microsomes with benzphetamine or aniline in the presence of NADPH-generating system
.
The cytochrome P-M-5 0 content of the micro-
somes was determined by the procedure of Omura and Sato 1 7 .
608
DALVI AND ROBBINS Amount of protein in each sample was estimated
using biuret method modified to include deoxycholate in the samples-*- • RESULTS AND DISCUSSION
Downloaded by [Universite Laval] at 04:13 05 March 2015
The results presented in Table 1 are from an experiment in which rats with initial body weight in the range of 90-110 g were divided into five groups each containing 10 animals and exposed to 0, 5, 10, and 2 0 ppm of cadmium in drinking water for a period of 8 weeks.
As can be seen from Table 1, gain in body
weight of the treated animals did not significantly differ from that of the control group.
Further, in
order to assess the effect of cadmium treatment on the in vivo metabolism of pentobarbital, 5 rats from each group were given a hypnotic dose of pentobarbital (50 mg/kg, ip) 2>+ hr post-termination of the experiment and the duration of hypnosis was measured as the time elapsed between losing and regaining the righting reflex.
It is evident from the data (Table 1) that
chronic exposure to cadmium up to 2 0 ppm did not result in a significant change in the capacity of rat liver microsomal enzymes to metabolize pentobarbital. Simultaneously, remaining 5 animals from each group were sacrificed by decapitation and hepatic microsomes isolated to examine their ability to metabo-
TABLE 1
g
Downloaded by [Universite Laval] at 04:13 05 March 2015
M O
Effi o.. of Chronic Cadmium Treatment (8 weeks) on Body Weight Gain, Pentobarbital-Induced Hypnosis and Components of Microsomal DrugMetabolizing Enzyme System a Cadmium • in Initial Body Duration drinking body weight of water weight gair hypnosis (ppm) (g/rat) (g/rat) (min)
a
Hepatic microsomal enzymes Benzphetamine Aniline N-demethyhydroxyCytochrome laseb laseG P-450 d
0
97
247
52 + 8
4.12 +_ 0.33
0.37 +_ 0.01
0.82 +_ 0.03
5
94
258
57 +_ 5
4.73 +_ 0.29
0.41 + 0.0H
0.78 +_ 0.05
10
106
259
53 +_ 4
4.65 +_ 0.36
0.39 +_ 0.03
0.73 +_ 0.02
20
110
264
58 +_ 8
4.45 +_ 0.24
0.41 +_ 0.07
0.84 +_ 0.06
w
^ g g n
^ § §
Results are expressed as the mean of 5 determinations +_ S.E.M.
"nmoles formaldehyde formed/min/mg of microsomal protein c
nmoles p-aminophenol formed/min/mg of microsomal protein nmoles/mg of microsomal protein
CTv O
610
DALVI AND ROBBINS
lize benzphetamine as a type I substrate and aniline as a type II substrate in vitro.
An aliquot-from each
sample was also used to determine the cytochrome P-450 content.
The results (Table 1) indicate that there is
no appreciable difference in the rate of metabolism of benzphetamine or aniline by microsomal enzymes from the
Downloaded by [Universite Laval] at 04:13 05 March 2015
control and the treated rats.
Similarly, the various
levels of cadmium did not affect the amount of cytochrome P-i^O, the major component of the drug-metabolizing enzyme system.
Thus the data on the in vivo
metabolism of pentobarbital are in agreement with the in vitro metabolism of benzphetamine and aniline confirming the contention that animals chronically exposed to cadmium up to 2 0 ppm in drinking water over a period of 8 weeks do not show impairment in their ability to metabolize drugs or other foreign chemicals. During the course of the chronic experiment, it was observed that a rat weighing about 350 g had daily water intake of 30-40 ml.
Based on these observations,
it is calculated that rats on 20 ppm cadmium in drinking water received a daily oral dose of the metallic toxicant equivalent to approximately 2 mg/kg. Therefore, for the comparison, a single 2 mg/kg dose of cadmium was administered ip to a group of normal rats and its effect on hepatic drug metabolism was studied 7 2 hr following the treatment.
The results shown in
CHRONIC EXPOSURE TO CADMIUM
611
Table 2, demonstrate that the single 2 mg/kg ip dose of cadmium caused singificantly greater prolongation of pentobarbital sleeping time even at 72 hr after the treatment suggesting the inhibition of the microsomal enzymes by cadmium.
When liver microsomes isolated
from the control and the cadmium-treated animals incuDownloaded by [Universite Laval] at 04:13 05 March 2015
bated with benzphetamine or aniline a substantial loss
of the activity of benzphetamine N-demethylase and aniline hydroxylase was noted in the treated versus control animals.
Likewise, there was a considerable
loss of microsomal cytochrome P-450 in the treated animals. As previously reported by several workers 1 3 "^,
these data confirm that 2 mg/kg dose of cadmium given ip to rats causes significant inhibition of the microsomal biotrasformation enzymes.
However, an almost
equal daily dose of cadmium given orally does not cause inhibitory effect on the drug-metabolizing enzyme system.
This may be attributed to the fact that gastro-
intestinal absorption of cadmium could be poor due to the presence of feed in the stomach
.
It should also
be noted that the presence of other minerals in diet such as calcium can reduce the absorption of cadmium from the stomach^0.
Furthermore, in chronic experiment,
the total daily intake of cadmium was distributed over a period of 24 hr.
Therefore, it is possible that
Downloaded by [Universite Laval] at 04:13 05 March 2015
TABLE 2 Effect of a Single Dose of Cadmium (2 mg/kg, ip) on Pentobarbital-Induced Hypnosis and Components of Microsomal Drug-Metabolizing Enzyme Systema
Hepatic microsomal enzymes
Treatment
Duration of hypnosis (min)
Benzphetamine N-demethylaseb
Aniline hydroxylase0
Cytochrqme P-450
Control
67 +_ 7
3.89 + 0.40
0.21 + 0.09
0.77 +0.07
Cadmium
117 + 11
1.94 + 0.29
0.14 + 0.05
0.47 + 0.05
Results are expressed as the mean of 5 determinations + S.E.M. nmoles formaldehyde formed/min/mg of microsomal protein
I
"nmolen p-aminophenol. formed/min/ng of microsomal protein nmo] en/rng of microsomal protein
63 H 2!
CHRONIC EXPOSURE TO CADMIUM
613
enough concentration of absorbed cadmium would not be present at a given time in the liver to cause inhibition of microsomal enzymes.
As reported previously, chronic
exposure to cadmium results in the induction of cadmium binding protein known as metalloghionein 21 . This
Downloaded by [Universite Laval] at 04:13 05 March 2015
specific protein binding of cadmium may, in part, account for some protection of the microsomal enzymes. Thus, these studies indicate that chronic exposure to cadmium up to 2 0 ppm in drinking water over a period of 8 weeks is unlikely to affect hepatic drug metabolism.
REFERENCES 1.
Webb, M., Brit. Med. Bull., 31, 246-250 (1975)
2.
Exon, J. H. , J. G. Lamberton, and L. D. Koller, Bull. Environ. Contam. Toxicol., 18, 74-76 (1977)
3.
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Received:
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