Toxicology Letters, 11 (1982) 31-34 Elsevier Biomedical Press

31

ACUTE TOXICITY OF PROPOXUR ON CARBOHYDRATE METABOLISM OF INDIAN CATFISH (HETEROPNEUSTES FOSSILIS)

ANIL K. SRIVASTAVA and NARENDRA N. SINGH

Department of Zoology, University of Gorakhpur, Gorakhpur 273001, U. P. (India)

(Received December 8th, 1980) (Accepted October 13th, 1981)

SUMMARY

Exposure of Indian catfish (Heteropneustes fossilis) to 5.20 ppm propoxur for 3, 6, 12, 48 and 96 h caused muscle glycogen depletion at 12 h and hepatic glycogenolysis at 3, 12,48 and 96 h; hyperglycemia developed at all time-intervals. Blood pyruvate levels increased significantly at 12 and 48 h. Hyperlac- ticemia was observed at 6 h but hypolacti~emia resulted at 12, 48 and 96 h in pesticide-treated fish. The observed effects are explained in terms of acute stress syndrome; possible mechanisms underlying the effect of anticholinesterase action of propoxur on carbohydrate metabolism are also discussed.

INTRODUCTION

Fish exposed to stressful conditions elicit neuroendocrine responses [I]; both

catecholamines [2] and adrenocorticosteroids [3] are secreted in increased amounts

which cause marked changes in carbohydrate energy reserves of fish [2,4, 51. SevinO

has been shown to disrupt carbohydrate and protein metabolism and cellular

energetic processes in the rat (61. This paper examines effects of time on carbohy-

drate metabolism of freshwater Indian catfish, Heteropneustes fossilis, after acute

exposure to a sublethal concentration of propoxur (n-methyl-2-isopropoxyphenyl-

carbamate; Bayer India Ltd.).

MATERIALS AND METHODS

Adult females of Indian catfish (weight 35.88 + 2.51 g; length 15.50 ?Z 0.64 cm)

were acclimatized for 10 days in tap water at ambient temperature (22.7 -+ 1.7 “C)

and under natural photoperiod. They were fed daily with dried ground shrimp and

flour pellets 171; food was withheld 12 h before and during the experiments. The

properties of the test water were: pH 7.71 t 0.01; electrical conductivity

0378.4274:82/0(~-0000/$02.75 ‘i, Elstvier Biomedical Press

32

418.24 & 87.54 pmho/cm; hardness 118.4 + 5.74 mg/l (as CaCOs); dissolved oxygen content 6.21 + 0.20 mg/l.

The 96 h LC50 value, based on measured concentrations [S], for propoxur was 6.50 ppm. Groups of 15 fish each (5 fish/20 1) were exposed to 5.20 ppm propoxur solution, in absolute alcohol, for 3,6, 12,48 and 96 h, and sampled for muscle and hepatic glycogen contents and blood glycose, pyruvate and lactate levels. Overall mortality among treated groups of fish was < 3%; however, only 6 fish from each group were impartially selected for the analyses of blood and tissue carbohydrate metabol~tes. Groups of control fish (n = 6) in tap water, containing an equal aliquot of solvent as treated fish, were sampled at 96 h for each parameter. This was done because pilot experiments showed that there was no significant effect of time on levels of carbohydrate metabolites amongst the controls.

At autopsy, the fish were anesthetized with 1 g/3 1 MS 222 for 2 minutes. Blood from fish was collected from the severed caudal peduncle into titrated tuberculin syringes for determination of blood glucose, pyruvate and lactate [9]. Pieces of liver and epaxial musculature just below the dorsal fin were excised for the determination of liver and muscle glycogen [IO], respectively.

RESULTS AND DISCUSSION

The effects of duration of exposure to 5.20 ppm propoxur on carbohydrate metabolites of fish are given in Table I. Earlier studies have shown that fish under stress secrete increased amounts of catecholamines and elicit depletion of muscle and hepatic glycogen reserves [2, 51. Thus, marked glycogenolysis in muscle at 12 h

TABLE I

CARBOH~D~TE METABOLITE VALUES OF INDIAN CATFISH EXPOSED TO 5.20 ppm PROPOXUR FOR VARIOUS TIME INTERVALS

Values are mean k SEM of 6 observations.

Parameter Control

Exposure period (h)

3 6 12 48 96

Muscle glycogen 0.34

(mg/lOO mg wet wt) * 0.02

Liver glycogen 12.64

(mg/lOO mg wet wt) i 1.10

Blood glucose 32.93

(mg/ 100 ml) IO.88

Blood pyruvate 0.35

(mg/ 100 ml) + 0.03

Blood lactate 21.94

(mg/lOO ml) + 2.95

0.38

+ 0.01

7.10

k 0.60”

45.52

ir 2.91h

0.37

t 0.03

28.45

i- 4.55

0.33

i- 0.02

14.65

li- 1.39

48.47

k 1 .?@

0.41

* 0.05

so.45

i 7.3lb -~

0.27

I 0.01 h

7.49

-t O.&h

75.52

+- 2.57c

0.40

+- 0.03c

17.14

+ 2.25b

0.35

+ 0.02

8.69

t 0.89a

44.03

t 1.32~

0.48

+ 0.02b

11.08

+ 1.13c

0.32

+ 0.01

8.30

rt o.9Oh

47‘35

f 1.24c

0.34

I: 0.02

8.88

-?r 0.32” ___...~

“P < 0.05; bP < 0.02-0.01; CP < 0.001 (Student r-test).

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and in liver at 3, 12, 48, and 96 h in fish after exposure to propoxur was possibly caused by a stress-induced increase in catecholamines.

Hyperglycemia develops both in fish and mammals during acute exposure to a variety of pesticides, including carbamates [l l-141. Little is known about the mechanism underlying the effect of anticholinesterase action of carbamate pesticides on carbohydrate metabolism. Nevertheless, both organophosphate and carbamate pesticides cause accumulation of acetylcholine with a concomitant increase in the output of catecholamines in mammals [15-171. Exogenous acetylcholine to fish leads to an increased secretion of catecholamines [18]; hence, the latter may induce glycogenolysis and hyperglycemia through the involvement of adenyl cyclase [ 191. Evidently, the stress-induced hyperglycemic response throughout the exposure period in this study was produced by mobilization of hepatic and, to some extent, muscle glycogen reserves.

Catecholamines can cause hyperlacticemia in fish directly [5]. Consequently, propoxur-induced hyperlacticemia at 6 h reflects a stress hormone-mediated response. The hypolacticemic response at 12, 48, and 96 h after pesticide treatment is unusual. Nevertheless, a hypolacticemic response to cadmium treatment was obtained in flounders, even though muscle glycogen had decreased [20]. Marked increases in blood pyruvate values in treated fish at 12 and 48 h may be due to oxygen debt being paid off by these time-intervals; this would reverse the direction of equilibrium so that increased lactate would be reconverted into pyruvate and metabolised through the Kreb’s cycle. The rate of oxygen consumption increases by as much as 40-70% from 24 to 48 h in several teleosts subjected to pesticides, including carbamates [21, 221.

The observations in this study are consistent with results obtained by other environmental biologists in fish subjected to pesticides [23, 241. Thus, evaluation of carbohydrate metabolites in fish may be a powerful method in anticipating the adverse impact of pesticides on fish.

ACKNOWLEDGEMENT

A Senior Research Fellowship to N.N.S. from the Indian Council of Scientific and Industrial Research is gratefully acknowledged.

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34

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