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The effects of acute and subacute sodium arsenite administration on carbohydrate metabolism
TOXICOLOGY
AND
The Effects
TAGHI Departmeni Environmental
APPLIED
PHARMACOLOGY%,
126-130 (1980)
of Acute and Subacute on Carbohydrate GHAFGHAZI,
of Pharmacology, Toxicology.
JAMES
Sodium Arsenite Metabolism
W. RIDLINGTON,’
AND BRUCE
School of Medicine, University of lsfahan. Isfahan, National Institute of Environmental Health Sciences. North Carolina 27709
Received
August
21, 1979; accepted
April
Administration
A. FOWLER Iran, and Laboratory of Research Triangle Park.
22, 1980
The Acute and Subacute Effects of Sodium Arsenite Administration on Carbohydrate Metabolism, GHAFGHAZI. T., RIDLINGTON, J. W., AND FOWLER, B. A. (1980). Toxicol. Appl. Pharmacol. 55,126- 130. The effects ofacute and subacute trivalent arsenic (As) administration on blood glucose levels, glucose tolerance, and mitochrondrial respiration were studied in male rats injected with sodium arsenite at 0, 5, or 10 mg/kg body wt and killed after 1.5 or 3 hr or 7 days. Hyperglycemia and glucose intolerance were observed in rats which received single acute doses of As. Hyperglycemia. but not glucose intolerance, was found to be abolished, in As-treated adrenalectomized animals. No measureable changes in hepatic mitochondrial respiratory function were noted in animals killed at 1.5 or 3 hr following As administration. Animals injected with 10 mg As/kg for 7 days showed hyperglycemia and marked glucose intolerance at 24 hr after the last injection. Mild depression of pyruvate/malate mediated state 3 mitochondrial respiration and decreased respiratory control ratios were observed for hepatic mitochondria isolated from arsenite injected rats in comparison with controls at this time point. The findings of this study indicate that arsenical disturbance of in vivo carbohydrate metabolism is a complex phenomenon which involves a number of organ systems and their functional interrelationships.
Arsenic (As) is a common environmental agent (Fowler, 1977) whose inhibitory effects on cellular carbohydrate metabolism have been studied by a number of investigators (Berry and Smythe, 1959; Havu, 1969; Peters, 1955). The exact mechanisms by which arsenicals interfere with carbohydrate metabolism in viva are not completely known but are attributed usually to the inhibitory effects of these agents on cellular respiration (Fowler and Woods, 1979; Fowler et al., 1977; 1979; Bencko et al., 1970; Bencko and Simane, 1968). Effects of arsenic on normal regulation of cellular carbohydrate metabolism have received rel‘Present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, Or. 97331.
atively little attention, but such data are of potentially great significance with respect to understanding the overall in viva impact of arsenicals on vital metabolic processes. In previous studies (Ghafghazi and Mennear, 1973) it has been shown that metals such as cadmium are capable of altering adrenal gland regulation of glucose metabolism in viva. The present study was undertaken to evaluate the effects of acute and subacute trivalent arsenic exposure on carbohydrate metabolism in rats. Emphasis was placed on relating changes in blood glucose levels and regulation of glucose tolerance to changes in hepatic mitochondrial respiration and the influence of adrenal glands on in vivo glucose utilization. 126
ARSENIC
EFFECTS OF CARBOHYDRATE
METHODS
---Adrenalectomwed
Treatment of animals. Intact or adrenalectomized male Charles River CD rats were divided in three groups and given a single ip injection of arsenic as sodium arsenite at dose levels of 0, 5, or 10 mg As/kg body wt. Control rats were injected with saline. For acute replicate studies, four animals per group were killed at 1.5 or 3 hr after injection. Rats in the subacute experiment received single daily injections of the above doses for 7 days prior to sacrifice. All adrenalectomized rats were maintained on laboratory chow and 0.9% NaCl drinking water. Nonadrenalectomized rats were maintained on laboratory chow and distilled drinking water. Blood samples for all time points were obtained by orbital sinus puncture. Mifochondrial respiration studies. Hepatic mitochondria from control and arsenic-treated animals were isolated as previously described (Fowler and Woods, 1977). Respiration studies were conducted using a Clark-type oxygen electrode and the reaction mixture of Nelson (1975) with a mitochondrial protein concentration of I mgiml. Initial state 4 respiration was produced by addition of 50 mM pyruvateimalate. State 3 respiration was induced by injection of 1.8 mM ADP. Mitochondrial respiratory control ratios (RCR) were assessed by dividing the ADP induced state 3 rate by the state 4 rate (state 4b) which followed utilization of the added ADP. Mitochondrial protein concentrations were determined using the method of Lowry et al. (1951). Blood
glucose
levels
and
glucose
tolerance
tests.
Blood glucose values and glucose tolerance tests were assessed as previously described (Ghafghazi and Mennear, 1973) using the glucose oxidase method (Glucostat, Worthington Biochemical Corp.).
0A.s (5.0mglkg) -As (IO.Omg/kg)
$200
1
n 0 Time
ii t
1
I 0
1.5 Time after arsenic
3 (hr)
FIG. 2. Comparative effects of arsenic on resting blood glucose in intact and adrenalectomized rats. Each point plus brackets represents mean ? SEM values for four intact and four adrenalectomized rats. Significant differences (p < 0.001) were observed at I .5and 3-hr intervals.
Statistical analysis. Intergroup comparisons were made using the Mann-Whitney U test (Noether, 1967).
RESULTS Acute Studies Hepatic mitochondrial respiration studies. No measurable differences in respira-
tory function of mitochondria using pyruvate malate substrates were observed between control and arsenite-treated rats at 1.5 or 3 hr following treatment. Blood glucose levels and glucose tolerance studies. The results of acute arsenite
*control
2
127
METABOLISM
1.5 afterarsenic
3
FIG. 1. Effect of sodium arsenite ip on resting blood glucose concentrations in rats. Each point plus brackets represent mean 2 SEM glucose values for four rats. Significant differences @ < 0.01) were found for both As treatment groups relative to control at both 1.5and 3 hr time points.
administration on blood glucose levels in intact rats are given in Fig. 1. Doses of 5 and 10 mg As/kg were administered ip, and blood glucose concentrations were measured 1.5 and 3 hr after treatment. The data indicate that both doses of As produce a statistically significant @ < 0.01) increase in blood glucose values. Figure 2 demonstrates the comparative effects of 10 mg As/ kg on the resting blood glucose concentrations of intact and adrenalectomized rats. It can be seen from these results that Asinduced hyperglycemia in intact rats is mediated through the adrenal glands since this
128
GHAFGHAZI,
RIDLINGTON,
effect was not observed in adrenalectomized animals. The effects of a single dose of As (10 mg As/kg) on glucose tolerance of intact and adrenalectomized rats are given in Fig. 3. For this experiment, arsenic was administered 60 min prior to the injection of the glucose. Blood glucose concentrations were determined 15, 30, and 60 min after the injection of glucose. These data indicate a marked interference in the ability of arsenitetreated animals to reduce blood glucose values in comparison with controls. The magnitude of change in blood glucose levels in Astreated adrenalectomized animals is much less than that observed in As-treated intact rats, but the values are significantly (p <0.05) different from those adrenalectomized control rats which had been pretreated with only saline at the 0-, 15, and 30-min time points. Subacute
Studies
Hepatic mitochondrial respiration studies. The effects of arsenite on respiratory function of mitochondria isolated from control and arsenite-injected animals after 7 days of treatment are given in Fig. 4. Depression of pyruvate/malate mediated state
-Intact
I
I 0
.control
15 30 TI me aft& glucose administmtion
60 (min)
FIG. 3. Comparison of glucose tolerance tests for intact and adrenalectomizied rats. As (10 mgikg, ip) was administered 60 min prior to the administration of glucose (2 g/kg, ip). Each point represents the mean r SEM of four rats. Significant differences @ < 0.05) were detected at all time intervals.
AND
FOWLER
-r
wkg
.O?fiatoms O2 L +I lmin It
FIG. 4. Effects of subacute arsenite administration on hepatic mitochondrial respiratory function in intact rats for pyruvateimalate mediated respiration. Note mild decrease in state 3 respiration and decreased respiratory control ratios for the arsenite treatment groups relative to controls.
3 mitochondrial respiration and increased state 4 respiration following utilization of the added ADP (state 4 b) with corresponding reduction of RCR values were observed. Blood glucose levels and glucose tolerance studies. Blood glucose was determined 24 hr after the final injection of As. It can be seen from these results (Table I) that the repeated administration of As (IO mg As/kg) increases the resting level of blood glucose significantly (p < 0.05). The same animals were used to determine the effect of repeated doses of As on glucose tolerance. In this experiment blood glucose was determined at 15,30, and 60 min after the administration of glucose. The results shown in Fig. 5 demonstrate that the repeated administration of As for 7 days significantly (p < 0.05) reduced the tolerance of the same animals to a glucose load at IS- and 30-min intervals for both doses and at the 60-min intervals for both doses and at the 60-min interval for the 10 mg As/kg dose. DISCUSSION Results of the present study indicate that acute and subacute administration of triva-
ARSENIC
EFFECTS
OF CARBOHYDRATE
lent arsenic to rats results in marked disturbances of carbohydrate metabolism. The hyperglycemic response to a single injection of As appears to be mediated by effects on the adrenal glands since it is abolished by adrenalectomy. This phenomenon is similar to that previously observed with cadmium (Ghafghazi and Mennear, 1973) which appears to involve altered adrenal gland release of catecholamines. The observed Asinduced intolerance to glucose load in adrenalectomized rats, however, indicates that this phenomenon is not exclusively mediated through the adrenals and that a second mechanism involving decreased tissue utilization or pancreatic function may be operating. Respiratory function of hepatic mitochondria isolated from arsenite-treated rats was found to be mildly depressed for pyruvate/malate supported respiration after 7 days of treatment. This effect is consistent with the findings of others (Peters, 1955; Bencko and Simane, 1968; Bencko et al., 1970; Fowler and Woods, 1979; Fowler et al., 1977; 1979) and is thought to result from arsenical inhibition of the pyruvate dehydrogenase complex (Peters, 1955; Schiller er al., 1978). Decreased tissue utilization of glucose probably plays a role in the observed hyperglycemia and glucose intolerance, but the measurable magnitude of this effect in mitochondria isolated from As target organ such as the liver appears to be TABLE
1
EFFECT OF SUBACUTE ARSENIC ADMKWSTRAT~ON ON RESTING BLOOD GLUCOSE IN RATS” Treatment
mg/lOO ml t SE
As (5.0 mg/kg x 7 days) As (10.0 mg/kg x 7 days)
93.00 of-2.73 92.25 r+_2.00 100.98 ? 2.40*
Control
” Arsenic or saline were administered by intraperitoneal injection into groups of four rats daily for 7 days. Blood glucose was determined 24 hr after the final injection of As. D Significantly different from control group (p < 0.05).
129
METABOLISM
.control .Ar(5.0mg/kgx
2 E 0
oAs(lO.Omg/kgx
7days) Tdoys)
$I,,,
, 0
I.5
30
60
Tomeafter glucose administration (min)
FIG. 5. Effects of subacute exposure to arsenic on glucose tolerance in intact rats. Treated rats received seven daily injections of As (5 or 10 mg As/kg, ip) and controls received seven daily injections of saline. Glucose (2 g/kg, ip) was administered 24 hr after final injection of As or saline. Each point represents mean + SEM of four rats. Significant differences @ < 0.05) were detected at the 15- to 30-min intervals for both doses and at a 60-min interval for the higher dose.
relatively small at the doses and time periods employed in the present study. It has also been reported that the accumulation of As in pancreatic islet tissue of the body fish Cot&s scorpius is associated with P-cell necrosis and hyperglycemia (Havu, 1969). The hyperglycemic effect of As observed in this study could be mediated partially by inhibiting insulin secretion. Further studies on the effects of acute and chronic exposure of As on insulin secretion are needed to clarify this consideration in mammalian species. In conclusion, results of the present study indicate that short-term arsenical perturbation of carbohydrate metabolism is a complex phenomenon which involves both direct target tissue carbohydrate metabolism and homeostatic organ systems which regulate overall in vivo glucose metabolism. The chronic effects of arsenic on these systems and alteration of carbohydrate metabolism in man by environmental exposure to arsenic require further study. REFERENCES BENCKO, V., MOKRY, Z., AND NEMECKOVA, H. (1970). The metabolic oxygen consumption by mouse liver homogenate during drinking water arsenic exposure. C’esk Hyg. 15, 305-308.
130
GHAFGHAZI,
RIDLINGTON,
BENCKO, V., AND SIMANE, F. (1968) The effect of chronical intake of arsenic on the liver tissue respiration in mice. Experientia 24, 706. BERRY, L. J., AND SMYTHE, D. S. (1959). Carbohydrate metabolism in normal and altitude exposed mice following arsenite posioning. Amer. J. Physiol. 197, 137- 140. FOWLER, B. A. (1977). Toxicology of environmental arsenic. In Advances in Modern Toxicology, Vol. 2. Toxicology of Trace Elements (R. A. Goyer and M. A. Mehlman, eds.), pp. 79-122. Hemisphere, Washington, D. C. FOWLER, B. A., AND WOODS, J. S. (1977). The transplacental toxicity of methyl mercury to fetal rat liver mitochondria. Lab. Invest. 36, 122- 130. FOWLER, B. A., AND WOODS, J. S. (1979). The effects of prolonged oral arsenate-exposure on liver mitochondria of mice: Morphometric and biochemical studies. Toxicol. Appl. Pharmacol. 50, 177-187. FOWLER, B. A., WOODS, J. S., AND SCHILLER, C. M. (1977). Ultrastructural and biochemical effects of prolonged oral arsenic exposure on liver mitochondria of rats. Environ. Health Perspec. 19, 197-204. FOWLER, B. A., WOODS, J. S., AND SCHILLER, C. M.
AND FOWLER
(1979). Studies of hepatic mitochondrial structure and function: Morphometric and biochemical evaluation ofin vivo perturbation by arsenate. Lab. Invest. 41,313-320.
GHAFGHAZI, T., AND MENNEAR, J. H. (1973). Effects of acute and subacute cadmium administration on carbohydrate metabolism in mice. Toxicol. Appl.
Pharmacol.
26, 23 I-240.
HAVU, N. (1969). Sulfhydryl inhibitors and pancreatic islet tissue. Acta Encocrinol. Suppl. 139, l-23 1. LOWRY, 0. H., ROSEBROUGH,N. J., FARR, A. L.. AND RANDALL, R. J. (1951). Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193, 265-275.
NELSON, B. D. (1975). The action of cyclodiene pesticides on oxidative phosphorylation in rat liver mitochondria. Biochem. Pharmacol. 24, 1485- 1490. NOETHER, G. E. (1967). Elements of Nonparametric Statistics, pp. 31. Wiley, New York. PETERS, R. A. (1955). Biochemistry of some toxic agents. I. Bull. Johns Hopkins Hosp. 97, 1-20. SCHILLER, C. M., FOWLER, B. A., AND WOODS, J. S. (1978). Pyruvate metabolism after in vivo exposure to oral arsenic. Chem. -Biol. Interact. 22. 25-33.
AND
The Effects
TAGHI Departmeni Environmental
APPLIED
PHARMACOLOGY%,
126-130 (1980)
of Acute and Subacute on Carbohydrate GHAFGHAZI,
of Pharmacology, Toxicology.
JAMES
Sodium Arsenite Metabolism
W. RIDLINGTON,’
AND BRUCE
School of Medicine, University of lsfahan. Isfahan, National Institute of Environmental Health Sciences. North Carolina 27709
Received
August
21, 1979; accepted
April
Administration
A. FOWLER Iran, and Laboratory of Research Triangle Park.
22, 1980
The Acute and Subacute Effects of Sodium Arsenite Administration on Carbohydrate Metabolism, GHAFGHAZI. T., RIDLINGTON, J. W., AND FOWLER, B. A. (1980). Toxicol. Appl. Pharmacol. 55,126- 130. The effects ofacute and subacute trivalent arsenic (As) administration on blood glucose levels, glucose tolerance, and mitochrondrial respiration were studied in male rats injected with sodium arsenite at 0, 5, or 10 mg/kg body wt and killed after 1.5 or 3 hr or 7 days. Hyperglycemia and glucose intolerance were observed in rats which received single acute doses of As. Hyperglycemia. but not glucose intolerance, was found to be abolished, in As-treated adrenalectomized animals. No measureable changes in hepatic mitochondrial respiratory function were noted in animals killed at 1.5 or 3 hr following As administration. Animals injected with 10 mg As/kg for 7 days showed hyperglycemia and marked glucose intolerance at 24 hr after the last injection. Mild depression of pyruvate/malate mediated state 3 mitochondrial respiration and decreased respiratory control ratios were observed for hepatic mitochondria isolated from arsenite injected rats in comparison with controls at this time point. The findings of this study indicate that arsenical disturbance of in vivo carbohydrate metabolism is a complex phenomenon which involves a number of organ systems and their functional interrelationships.
Arsenic (As) is a common environmental agent (Fowler, 1977) whose inhibitory effects on cellular carbohydrate metabolism have been studied by a number of investigators (Berry and Smythe, 1959; Havu, 1969; Peters, 1955). The exact mechanisms by which arsenicals interfere with carbohydrate metabolism in viva are not completely known but are attributed usually to the inhibitory effects of these agents on cellular respiration (Fowler and Woods, 1979; Fowler et al., 1977; 1979; Bencko et al., 1970; Bencko and Simane, 1968). Effects of arsenic on normal regulation of cellular carbohydrate metabolism have received rel‘Present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, Or. 97331.
atively little attention, but such data are of potentially great significance with respect to understanding the overall in viva impact of arsenicals on vital metabolic processes. In previous studies (Ghafghazi and Mennear, 1973) it has been shown that metals such as cadmium are capable of altering adrenal gland regulation of glucose metabolism in viva. The present study was undertaken to evaluate the effects of acute and subacute trivalent arsenic exposure on carbohydrate metabolism in rats. Emphasis was placed on relating changes in blood glucose levels and regulation of glucose tolerance to changes in hepatic mitochondrial respiration and the influence of adrenal glands on in vivo glucose utilization. 126
ARSENIC
EFFECTS OF CARBOHYDRATE
METHODS
---Adrenalectomwed
Treatment of animals. Intact or adrenalectomized male Charles River CD rats were divided in three groups and given a single ip injection of arsenic as sodium arsenite at dose levels of 0, 5, or 10 mg As/kg body wt. Control rats were injected with saline. For acute replicate studies, four animals per group were killed at 1.5 or 3 hr after injection. Rats in the subacute experiment received single daily injections of the above doses for 7 days prior to sacrifice. All adrenalectomized rats were maintained on laboratory chow and 0.9% NaCl drinking water. Nonadrenalectomized rats were maintained on laboratory chow and distilled drinking water. Blood samples for all time points were obtained by orbital sinus puncture. Mifochondrial respiration studies. Hepatic mitochondria from control and arsenic-treated animals were isolated as previously described (Fowler and Woods, 1977). Respiration studies were conducted using a Clark-type oxygen electrode and the reaction mixture of Nelson (1975) with a mitochondrial protein concentration of I mgiml. Initial state 4 respiration was produced by addition of 50 mM pyruvateimalate. State 3 respiration was induced by injection of 1.8 mM ADP. Mitochondrial respiratory control ratios (RCR) were assessed by dividing the ADP induced state 3 rate by the state 4 rate (state 4b) which followed utilization of the added ADP. Mitochondrial protein concentrations were determined using the method of Lowry et al. (1951). Blood
glucose
levels
and
glucose
tolerance
tests.
Blood glucose values and glucose tolerance tests were assessed as previously described (Ghafghazi and Mennear, 1973) using the glucose oxidase method (Glucostat, Worthington Biochemical Corp.).
0A.s (5.0mglkg) -As (IO.Omg/kg)
$200
1
n 0 Time
ii t
1
I 0
1.5 Time after arsenic
3 (hr)
FIG. 2. Comparative effects of arsenic on resting blood glucose in intact and adrenalectomized rats. Each point plus brackets represents mean ? SEM values for four intact and four adrenalectomized rats. Significant differences (p < 0.001) were observed at I .5and 3-hr intervals.
Statistical analysis. Intergroup comparisons were made using the Mann-Whitney U test (Noether, 1967).
RESULTS Acute Studies Hepatic mitochondrial respiration studies. No measurable differences in respira-
tory function of mitochondria using pyruvate malate substrates were observed between control and arsenite-treated rats at 1.5 or 3 hr following treatment. Blood glucose levels and glucose tolerance studies. The results of acute arsenite
*control
2
127
METABOLISM
1.5 afterarsenic
3
FIG. 1. Effect of sodium arsenite ip on resting blood glucose concentrations in rats. Each point plus brackets represent mean 2 SEM glucose values for four rats. Significant differences @ < 0.01) were found for both As treatment groups relative to control at both 1.5and 3 hr time points.
administration on blood glucose levels in intact rats are given in Fig. 1. Doses of 5 and 10 mg As/kg were administered ip, and blood glucose concentrations were measured 1.5 and 3 hr after treatment. The data indicate that both doses of As produce a statistically significant @ < 0.01) increase in blood glucose values. Figure 2 demonstrates the comparative effects of 10 mg As/ kg on the resting blood glucose concentrations of intact and adrenalectomized rats. It can be seen from these results that Asinduced hyperglycemia in intact rats is mediated through the adrenal glands since this
128
GHAFGHAZI,
RIDLINGTON,
effect was not observed in adrenalectomized animals. The effects of a single dose of As (10 mg As/kg) on glucose tolerance of intact and adrenalectomized rats are given in Fig. 3. For this experiment, arsenic was administered 60 min prior to the injection of the glucose. Blood glucose concentrations were determined 15, 30, and 60 min after the injection of glucose. These data indicate a marked interference in the ability of arsenitetreated animals to reduce blood glucose values in comparison with controls. The magnitude of change in blood glucose levels in Astreated adrenalectomized animals is much less than that observed in As-treated intact rats, but the values are significantly (p <0.05) different from those adrenalectomized control rats which had been pretreated with only saline at the 0-, 15, and 30-min time points. Subacute
Studies
Hepatic mitochondrial respiration studies. The effects of arsenite on respiratory function of mitochondria isolated from control and arsenite-injected animals after 7 days of treatment are given in Fig. 4. Depression of pyruvate/malate mediated state
-Intact
I
I 0
.control
15 30 TI me aft& glucose administmtion
60 (min)
FIG. 3. Comparison of glucose tolerance tests for intact and adrenalectomizied rats. As (10 mgikg, ip) was administered 60 min prior to the administration of glucose (2 g/kg, ip). Each point represents the mean r SEM of four rats. Significant differences @ < 0.05) were detected at all time intervals.
AND
FOWLER
-r
wkg
.O?fiatoms O2 L +I lmin It
FIG. 4. Effects of subacute arsenite administration on hepatic mitochondrial respiratory function in intact rats for pyruvateimalate mediated respiration. Note mild decrease in state 3 respiration and decreased respiratory control ratios for the arsenite treatment groups relative to controls.
3 mitochondrial respiration and increased state 4 respiration following utilization of the added ADP (state 4 b) with corresponding reduction of RCR values were observed. Blood glucose levels and glucose tolerance studies. Blood glucose was determined 24 hr after the final injection of As. It can be seen from these results (Table I) that the repeated administration of As (IO mg As/kg) increases the resting level of blood glucose significantly (p < 0.05). The same animals were used to determine the effect of repeated doses of As on glucose tolerance. In this experiment blood glucose was determined at 15,30, and 60 min after the administration of glucose. The results shown in Fig. 5 demonstrate that the repeated administration of As for 7 days significantly (p < 0.05) reduced the tolerance of the same animals to a glucose load at IS- and 30-min intervals for both doses and at the 60-min intervals for both doses and at the 60-min interval for the 10 mg As/kg dose. DISCUSSION Results of the present study indicate that acute and subacute administration of triva-
ARSENIC
EFFECTS
OF CARBOHYDRATE
lent arsenic to rats results in marked disturbances of carbohydrate metabolism. The hyperglycemic response to a single injection of As appears to be mediated by effects on the adrenal glands since it is abolished by adrenalectomy. This phenomenon is similar to that previously observed with cadmium (Ghafghazi and Mennear, 1973) which appears to involve altered adrenal gland release of catecholamines. The observed Asinduced intolerance to glucose load in adrenalectomized rats, however, indicates that this phenomenon is not exclusively mediated through the adrenals and that a second mechanism involving decreased tissue utilization or pancreatic function may be operating. Respiratory function of hepatic mitochondria isolated from arsenite-treated rats was found to be mildly depressed for pyruvate/malate supported respiration after 7 days of treatment. This effect is consistent with the findings of others (Peters, 1955; Bencko and Simane, 1968; Bencko et al., 1970; Fowler and Woods, 1979; Fowler et al., 1977; 1979) and is thought to result from arsenical inhibition of the pyruvate dehydrogenase complex (Peters, 1955; Schiller er al., 1978). Decreased tissue utilization of glucose probably plays a role in the observed hyperglycemia and glucose intolerance, but the measurable magnitude of this effect in mitochondria isolated from As target organ such as the liver appears to be TABLE
1
EFFECT OF SUBACUTE ARSENIC ADMKWSTRAT~ON ON RESTING BLOOD GLUCOSE IN RATS” Treatment
mg/lOO ml t SE
As (5.0 mg/kg x 7 days) As (10.0 mg/kg x 7 days)
93.00 of-2.73 92.25 r+_2.00 100.98 ? 2.40*
Control
” Arsenic or saline were administered by intraperitoneal injection into groups of four rats daily for 7 days. Blood glucose was determined 24 hr after the final injection of As. D Significantly different from control group (p < 0.05).
129
METABOLISM
.control .Ar(5.0mg/kgx
2 E 0
oAs(lO.Omg/kgx
7days) Tdoys)
$I,,,
, 0
I.5
30
60
Tomeafter glucose administration (min)
FIG. 5. Effects of subacute exposure to arsenic on glucose tolerance in intact rats. Treated rats received seven daily injections of As (5 or 10 mg As/kg, ip) and controls received seven daily injections of saline. Glucose (2 g/kg, ip) was administered 24 hr after final injection of As or saline. Each point represents mean + SEM of four rats. Significant differences @ < 0.05) were detected at the 15- to 30-min intervals for both doses and at a 60-min interval for the higher dose.
relatively small at the doses and time periods employed in the present study. It has also been reported that the accumulation of As in pancreatic islet tissue of the body fish Cot&s scorpius is associated with P-cell necrosis and hyperglycemia (Havu, 1969). The hyperglycemic effect of As observed in this study could be mediated partially by inhibiting insulin secretion. Further studies on the effects of acute and chronic exposure of As on insulin secretion are needed to clarify this consideration in mammalian species. In conclusion, results of the present study indicate that short-term arsenical perturbation of carbohydrate metabolism is a complex phenomenon which involves both direct target tissue carbohydrate metabolism and homeostatic organ systems which regulate overall in vivo glucose metabolism. The chronic effects of arsenic on these systems and alteration of carbohydrate metabolism in man by environmental exposure to arsenic require further study. REFERENCES BENCKO, V., MOKRY, Z., AND NEMECKOVA, H. (1970). The metabolic oxygen consumption by mouse liver homogenate during drinking water arsenic exposure. C’esk Hyg. 15, 305-308.
130
GHAFGHAZI,
RIDLINGTON,
BENCKO, V., AND SIMANE, F. (1968) The effect of chronical intake of arsenic on the liver tissue respiration in mice. Experientia 24, 706. BERRY, L. J., AND SMYTHE, D. S. (1959). Carbohydrate metabolism in normal and altitude exposed mice following arsenite posioning. Amer. J. Physiol. 197, 137- 140. FOWLER, B. A. (1977). Toxicology of environmental arsenic. In Advances in Modern Toxicology, Vol. 2. Toxicology of Trace Elements (R. A. Goyer and M. A. Mehlman, eds.), pp. 79-122. Hemisphere, Washington, D. C. FOWLER, B. A., AND WOODS, J. S. (1977). The transplacental toxicity of methyl mercury to fetal rat liver mitochondria. Lab. Invest. 36, 122- 130. FOWLER, B. A., AND WOODS, J. S. (1979). The effects of prolonged oral arsenate-exposure on liver mitochondria of mice: Morphometric and biochemical studies. Toxicol. Appl. Pharmacol. 50, 177-187. FOWLER, B. A., WOODS, J. S., AND SCHILLER, C. M. (1977). Ultrastructural and biochemical effects of prolonged oral arsenic exposure on liver mitochondria of rats. Environ. Health Perspec. 19, 197-204. FOWLER, B. A., WOODS, J. S., AND SCHILLER, C. M.
AND FOWLER
(1979). Studies of hepatic mitochondrial structure and function: Morphometric and biochemical evaluation ofin vivo perturbation by arsenate. Lab. Invest. 41,313-320.
GHAFGHAZI, T., AND MENNEAR, J. H. (1973). Effects of acute and subacute cadmium administration on carbohydrate metabolism in mice. Toxicol. Appl.
Pharmacol.
26, 23 I-240.
HAVU, N. (1969). Sulfhydryl inhibitors and pancreatic islet tissue. Acta Encocrinol. Suppl. 139, l-23 1. LOWRY, 0. H., ROSEBROUGH,N. J., FARR, A. L.. AND RANDALL, R. J. (1951). Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193, 265-275.
NELSON, B. D. (1975). The action of cyclodiene pesticides on oxidative phosphorylation in rat liver mitochondria. Biochem. Pharmacol. 24, 1485- 1490. NOETHER, G. E. (1967). Elements of Nonparametric Statistics, pp. 31. Wiley, New York. PETERS, R. A. (1955). Biochemistry of some toxic agents. I. Bull. Johns Hopkins Hosp. 97, 1-20. SCHILLER, C. M., FOWLER, B. A., AND WOODS, J. S. (1978). Pyruvate metabolism after in vivo exposure to oral arsenic. Chem. -Biol. Interact. 22. 25-33.