James D. Yarbrough

Xenobiotic biotransformation systems in fishes

Abstract The early speculations that fishes would not possess detoxication sytems because of the excretory activity of the gill have been shown to be wrong. Indeed, fishes are capable of xenobiotic metabolism by both microsomal oxidation, reduction and conjugation. Enzyme characteristics appear to be similar between fishes and mammals, with the exception of typically lower temperature optima in fishes which may reflect the usual lower operating temperatures of heterotherms as compared to homeotherms. Early reports of litte or no enzyme activity in fishes may very well have reflected a lack of knowledge of the lower temperature optima in fishes. However, even under optimized conditions, fishes demonstrate lower enzyme activities than mammals. Although reports are fragmentary, evolutionary trends can be observed among fishes with some biotransformation systems absent or less developed in the more primitive fishes as compared with more advanced fishes. The less effective induction system in fishes as compared to mammals might reflect the fact that fishes live in an environment in which toxicants are diluted, thereby reducing the response of enzymes to a xenobiotic challenge. The real significance of the xenobiotic biotransformation enzymes to the fish from an in vivo standpoint has not been extensively investigated. In a few cases the metabolism of a xenobiotic by fishes is known to affect its toxicity and it is entirely possible that the lower enzyme activities that fishes possess are sufficient for the disposition of the concentrations of toxicants that fishes ordinarily encounter. However, the aquatic environment is becoming more contaminated than ever before. From the little information available, we cannot predict whether fishes have the capability to adapt to and process these higher concentrations of toxicants. Therefore, further study of the biotransformation systems is essential so that an evaluation of fish-toxicant interactions can be made.

Parathion and methyl parathion toxicity to insecticideresistant and susceptible mosquitofish(Gambusia affinis)

SummaryThis study determined the toxicity of parathion and methyl parathion to organochlorine compound-resistant and -susceptible populations of mosquitofish (Gambusia affinis). Mosquitofish can tolerate about 40 times more methyl parathion than parathion. The resistant population demonstrates a 1.3 fold greater tolerance of methyl parathion than the susceptible population, which may be a developing resistance. The resistant population also demonstrates an environmentally-induced tolerance to parathion (1.6 fold) in the spring but no overall tolerance to parathion in the fall when compared to the susceptible population.

A seasonal study of microsomal mixed-function oxidase components in insecticide-resistant and susceptible mosquitofish, Gambusia affinis☆

Abstract The mixed-function oxidase components which are involved in xenobiotic hydroxylations were studied in liver microsomes from two populations of mosquitofish ( Gambusia affinis ) for 26 months. One population is highly resistant to organochlorine insecticides and is exposed periodically to agricultural chemical contamination; the other population is susceptible to these chemicals and is not exposed to such pollutants. The following parameters were measured: cytochromes P -450 and b 5 ; NADPH-cytochrome c , NADPH-dichloroindophenol, NADH-cytochrome c , and NADH-cytochrome b 5 reductases; liver weight to body weight ratios; and microsomal protein. Most parameters demonstrated seasonal cycles with the highest values occurring during the late fall and winter. The cyclic nature of the parameters investigated may be the result of the relative magnitude of microsomal hydroxylations during the year in relationship to other microsomal processes such as biosynthesis. The range of concentrations or specific activities of most of the components was about the same for both fish populations, although the resistant fish possessed relatively larger livers and, therefore, greater amounts of these microsomal components than the susceptible fish. The results suggest the induction of these microsomal oxidase components in the resistant population during their annual exposure to environmental pollutants in the agricultural runoff.

The in vivo effect of mirex on soluble hepatic enzymes in the rat

Abstract Adult male and female rats fed dietary mirex in concentrations of 10, 20, 30, 40, and 50 ppm for 4 weeks exhibited significant decreases in liver levels of lactic dehydrogenase, malic dehydrogenase, sorbitol dehydrogenase, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase as compared to control levels. Enzyme losses were cytoplasmic and decreased in magnitude with increased time of exposure and dietary mirex concentrations. Serum sorbitol dehydrogenase levels were increased above control levels during the first week of mirex exposure while hepatic sorbitol dehydrogenase levels were concomitantly decreased below the control levels. Hepatic glutamic oxaloacetic transaminase levels were significantly decreased during the first week for all dietary mirex concentrations as were the other enzymes at the 40 and 50 ppm mirex concentrations. The magnitude of the enzyme decreases in female rat tissue was consistently lower than enzyme decreases in the male rat tissue fed equivalent dietary mirex dosages. Liver weights for male rats increased significantly at all dietary mirex levels during week one. However, only animals receiving the 40 and 50 ppm dietary mirex levels showed significant liver weight increases at the end of week 4. Female rat liver weights were increased at the 30 and 40 ppm mirex dietary levels after 4 weeks. No significant differences in body weights were observed for any dietary level of mirex. Mirex hepatic residues appeared to be equal for both sexes. No gross histological alterations were observed following treatment.

Crude oil effects on microsomal mixed-function oxidase system components in the striped mullet (Mugil cephalus)

Abstract The effects of exposure to two types of crude oil on microsomal mixed-function oxidase system components in livers of juvenile striped mullet ( Mugil cephalus ) were investigated. Mullet were exposed for 4 days to emulsified Empire Mix or Saudi Arabian crude oils at an initial concentration of 75 ppm and an average of 1 ppm in the water column. Liver size was increased by about 50% following exposure to both oils. Since neither total hepatic protein nor microsomal protein increased as rapidly as did liver size, the concentrations of both were reduced following oil exposures. The proportion of microsomal protein to total hepatic protein or wet weight was not altered following crude oil exposure. Both cytochromes P-450 and b 5 were induced following oil treatment. NADPH-dependent enzymes assayed with cytochrome c and dichlorophenolindophenol as substrates showed increases in activity after exposure to Empire Mix crude oil but only the latter enzyme activity was increased on a microsomal protein basis following Saudi Arabian crude oil treatment. Activities of NADH cytochrome c and NADH cytochrome b 5 reductases appeared to vary with the protein level. However, since liver size was increased, oil-treated mullet had more of all parameters measured than did control mullet. Although the acute toxicity of Saudi Arabian crude oil to mullet is greater than that of Empire Mix crude oil, Empire Mix crude oil had greater inductive effects on microsomal oxidase components.

Liver response to oral administration of mirex in rats

Abstract Single oral doses of 50, 100, and 150 ppm of mirex stimulated liver enlargement at an initial rate which was dose independent. An apparent maximum response of the liver was obtained at 100 ppm of mirex. Hypertrophy was involved in the liver response. Changes in the liver concentration of lipid, deoxyribonucleic acid, and ribonucleic acid were observed. Protein, glycogen, and dry weight concentrations remained essentially unchanged. Hepatic and serum levels of lactate dehydrogenase, glutamic-pyruvic transaminase, and glutamic-oxaloacetic transaminase activity did not indicate that mirex caused liver cell damage. Sex hormones were apparently involved in the magnitude of the liver response. Mirex residue in the liver of male rats was most closely correlated with hepatic lipid concentration but was not significantly correlated in females.

Persistent vitellogenin-like protein and binding of DDT in the serum of insecticide-resistant mosquitofish (Gambusia Affinis)

1. During the reproductive season the serum of most oviparous teleosts contains an electrophoretically-identifiable protein, vitellogenin. 2. However, serum from insecticide-resistant mosquitofish contain a vitellogenin-like protein (VLP) year round. 3. It is suggested that estrogenic and/or proestrogenic xenobiotics from the environment of the fish induces the formation of this protein during the non-reproductive season. 4. In vitro incubation of [p,p′-3H]DDT with reproductive or non-reproductive resistant and susceptible fish serum, led to its association with three separate proteins (VLP, a low molecular weight lipoprotein and albumin). 5. Xenobiotics thus may induce the formation of protein (VLP), in non-reproductive resistant fish, which can bind and transport insecticides.

Physiological effects of crude oil exposure in the striped mullet, Mugil cephalus

Abstract Juvenile mullet ( Mugil cephalus ) were exposed to a surface slick of Empire Mix crude oil for a three week period in a simulated estuarine ecosystem. Liver weight to body weight ratios were increased in the mullet from the oil-treated ponds when compared to those from the control ponds. Activities of alkaline phosphatase, which were elevated in gill and muscle of oil-treated mullet, and β-glucuronidase, which was elevated in the muscle of oil-treated mullet, may be related to the degree of stress the animals were experiencing. Malic dehydrogenase, which was depressed in the livers and elevated in the muscle of oil-treated organisms, indicate changes in aerobic metabolism in response to the stress of crude oil exposure. Muscle acetylcholinesterase was not affected by oil exposure.

A study of liver function in rats with mirex-induced enlarged livers

Abstract The functional capacity of a mirex-induced, enlarged liver was studied in rats. The tests used were sulfobromophthalein clearance, hepatic cytochrome P -450 concentration, serum total protein concentration and electrophoretic pattern, serum total lipid concentration, serum glucose concentration, and the liver response to epinephrine. There was no indication of a loss of functional capacity in the enlarged liver. Sulfobromophthalein clearance and microsomal cytochrome P -450 concentration indicated an increase in total liver functional capacity. We conclude that mirex is not a direct hepatotoxin producing generalized parenchymal cell damage.

Acute toxicities of selected herbicides to fingerling channel catfish,Ictalurus punctatus

SummaryA scan of the acute toxicities of eighteen common herbicides to one-year-old channel catfish (Ictalurus punctatus) was conducted. Herbicides causing less than 10% mortality in 48 hr at 10 ppm were: alanap, chloramben, 2,4-D acid, 2,4-D dimethyl amine salt, dalapon, diuron, DSMA, EPTC, fluometuron, metribuzin, monuron, MSMA, nitralin and 2,4,5-T. The 96-hr LC50 values in ppb for four herbicides found toxic were: propanil, 3796; trifluralin, 417; bensulide, 379; and DNBP, 118. The toxicity of Dyanap®, a mixture of DNBP and alanap, was lower than that of DNBP; there was no apparent synergism between DNBP and alanap in the mixture.