Characterization of risks associated with the use of molinate.

A review of the toxicological information indicated that the most critical/sensitive toxicological endpoints of concern for human exposure to molinate, a thiocarbamate, preemergent herbicide, were adverse reproductive effects, neurotoxicity, and possible oncogenicity. Occupational and nonoccupational exposures to molinate potentially involved oral, dermal, and inhalation routes. Margins of safety for potential short-term, seasonal, annual, and lifetime exposures to workers associated with handling and application of molinate, the general public, and farmers were greater than the values conventionally recommended to protect people from the toxic effects of a chemical.

Influence of 2,5-hexanedione on rat brain amine synthesis and metabolism.

Sprague-Dawley derived rats were gavaged with daily doses of 2,5-hexanedione, a neurotoxic metabolite of both methyl n-butyl ketone and n-hexane. Seven daily doses of 0, 30, 100 or 300 mg 2,5-hexanedione/kg caused neuromuscular incoordination at the highest dose level while no effect was seen at the lowest level. Intravenous injections of either tritiated tyrosine or tryptophan, followed by exact time-interval sacrifices, facilitated the determination of synthesis rates and metabolism of various brain amines. At a cumulative dose of 210 mg 2,5-hexanedione/kg, the dopamine turnover rate was significantly increased, while precursor and metabolite levels were unchanged. Levels of serotonin as well as the serotonin synthesis rate remained unchanged, but levels of 5-hydroxyindoleacetic acid increased significantly in a dose dependent manner. The rise in 5-hydroxyindoleacetic acid levels inconjunction with no effects on other indoleamione parameters in 2,5-hexanedione-fed animals, suggests a possible inhibition of the energy-dependent 5-hydroxyindoleacetic acid efflux system in the brain.

Effect of temperature on the inhibition of rat brain synaptosomal ATPases by DDT and its structural analogs.

In vitro effects of DDT and its isomers or metabolites were studied on Na+-K+-ATPase and oligomycin-sensitive (OS) Mg++-ATPase activities at 17, 27 and 37 degrees C in rat brain synaptosomes. Dicofol and methoxychlor were found to be more effective inhibitors of Na+-K+-ATPase and OS Mg++-ATPase than DDT, DDD and DDE. Inhibition of OS Mg++-ATPase by the compounds tested (except DDE) was found to be greater at 17 degrees C than at higher temperatures (17 greater than 27 greater than 37 degrees C), suggesting a negative temperature correlation trend Na+-K+-ATPase was less sensitive to these compounds when compared with OS Mg++-ATPase and the inhibition was greater at higher temperatures (37 greater than 27 greater than 17 degrees C), suggesting a positive temperature correlation trend. Other DDT isomers and metabolites showed variable effects on Na+-K+-ATPase and OS Mg++-ATPases. DDD, but not DDE, inhibited both enzyme activities and the inhibition was independent of temperature. No significant differences were observed in the inhibitory potencies of the various DDT, DDD or DDE ring substitutes studied. The present data indicate that DDT, dicofol and methoxychlor were more effective inhibitors of OS Mg++-ATPase than Na+-K+-ATPase and that the inhibition of the former enzyme had a negative temperature dependence, a feature which parallels toxicity results in insects.

Lack of effects of chlordecone on synthesis rates, steady state levels and metabolites of catecholamines in rat brain.

Reports on effects of chlordecone on brain catecholamine concentrations have been inconsistent. Because various studies indicate the potential for toxic effects on neurotransmitter systems, the following study was performed to assess effects of chlordecone on brain adrenergic systems. Male Sprague-Dawley rats dosed once with chlordecone at 100 mg/kg were sacrificed after 24 hr, then brain norepinephrine (NE) and dopamine (DA) levels were assayed. Another group was fed chlordecone at 10 mg/kg for 10 days. Additionally, animals treated with 10 mg/kg/day were injected iv with 3H-tyrosine at two intervals prior to sacrifice in order to estimate NE and DA synthesis rates. Whole brain concentrations of NE, DA, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol sulfate (MOPEG-SO4) were measured. No changes were observed in whole brain catecholamine or metabolite concentrations, nor in NE or DA synthesis rates. In another experiment, administration of chlordecone (10 mg/kg for 10 days) was found not to alter the rate of incorporation of 3H-tyrosine into NE or DA in any brain area tested. Results suggest that the initial functional deficits responsible for neurological symptoms do not result from inhibition of synthesis and transport of brain catecholamines.

Effect of chlordecone on pH and temperature dependent substrate activation kinetics of rat brain synaptosomal ATPases.

Chlordecone, a polycyclic chlorinated insecticide known as Kepone, inhibited the activities of (Na+-K+)ATPase and Mg2+-ATPase in rat brain synaptosomes. Altered pH and specific activity curves for both enzymes demonstrated significant inhibition by chlordecone in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation by ATP in the case of (Na+-K+)ATPase was indicated by altered Vmax values with no significant change in Km values at any pH studied, except at pH 9.5. Mg2+-ATPase was inhibited uncompetitively as evidenced by altered Vmax and Km values. The activities of both ATPase were decreased in the presence of chlordecone at higher temperatures. Activation energy (delta E) values were found to be decreased significantly in the presence of chlordecone at 37 degrees. Arrhenius plots of both ATPases preincubated with chlordecone were found to be nonlinear. In the presence of chlordecone, Vmax was decreased without significant change in Km values for (Na+-K+)ATPase at all temperatures, suggesting a noncompetitive type of inhibition. In the case of Mg2+-ATPase, similar noncompetitive type inhibition was obtained at 27 degrees but not at 32 and 37 degrees. The kinetic data in general suggest that the chlordecone inhibited (Na+-K+)ATPase noncompetitively and Mg2+-ATPase uncompetitively at all pHs and temperatures studied. The present data suggest that inhibition of (Na+-K+)ATPase and Mg2+-ATPase, the two membrane-bound enzymes in synaptosomes, by chlordecone is temperature dependent and pH independent.

Evaluation of acrylamide treatment on levels of major brain biogenic amines, their turnover rates, and metabolites.

Acrylamide, a widely used and chemically active substance, has caused delayed distal neuropathy in man and in experimental animals. Male rats administered 50 mg/kg/day acrylamide for 5 days demonstrated ataxia in preliminary rotorod experiments. Additional groups of rats were dosed with 5, 15 or 50 mg/kg/day acrylamide for 5 days, then sacrificed on day 6 at various time intervals after iv injections of tritiated tyrosine (Tyr) or tryptophan (Trp). Brain levels of Tyr, Trp, norepinephrine (NE), dopamine (DA), serotonin (5-HT), and respective metabolites, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MOPEG-sulfate), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) were assayed fluorometrically. Turnover rates of NE, DA and 5-HT were estimated by evaluating the rates of specific activity changes in neurotransmitters and precursor amino acids over time. A slight reduction of whole brain NE content was observed in rats administered 50 mg/kg/day acrylamide. Other neurotransmitter levels were not affected by acrylamide levels administered, nor were turnover rates affected. Levels of MOPEG-sulfate and DOPAC were unchanged at any dose tested. Increased levels of 5-HIAA were observed in rats receiving 15 and 50 mg/kg/day acrylamide. Results suggest that acrylamide neurotoxicity does not entail widespread damage to the neurons associated with these biogenic amines; however, the acid metabolite efflux from brain was significantly inhibited.

Alterations in tissue distribution of chlordecone (kepone) in the rat following phenobarbital or SKF-525A administration.

Phenobarbital (PB) or SKF-525A were injected ip into adult male rats prior to administration of 1.6 microCi [14C] chlordecone (CD) by gavage. Effects of these liver function modulators on tissue distribution of CD was assessed. In all cases, animals were sacrificed at 24 h following [14C]CD gavage. The timing and number of injections of PB or of SKF-525A were varied. Doses of PB (65 mg/kg) or of SKF-525A (75 mg/kg) were used except as noted, and controls received saline. Specific radioactivities of major tissues were assayed by scintillation counting. Rats pre-treated with a single dose of SKF-525A at 6, 12, or 24 h prior to [14C]CD distribution. Similarly, PB administered at 6 h prior to [14C]CD gavage was without effect on distribution. Rats pretreated 12 or 14 h before [14C]CD with PB appeared to have increased liver specific activities and had reduced [14C]CD levels in several other tissues. These trends were more marked in a second study, in which multiple doses of PB (3 consecutive daily doses of 65 mg/kg, the final dose 24 h prior to [14C]CD or SKF-525A (1 dose of 75 mg/kg 90 min prior to [14C]CD, followed by a second dose of 38 mg/kg at 6.5 h after [14C]CD) were given. Tissue [14C]CD levels were assayed as before; urine and feces samples were also counted and reported as percent of [14C]CD administered. SKF-525A animals had significantly high [14C] levels in digestive system, while fecal and urinary levels were significantly low. No other significant alterations were observed in these animals, except that testes levels were reduced. Livers of rats receiving multiple doses of PB had significantly elevated [14C]CD levels, and all other tissues examined had levels significantly below controls. Fecal and urinary excretion of [14C]CD was significantly depressed. Studies indicate that an inducer of hepatic metabolism can dramatically alter the distribution and hence the relative toxicity of CD.

Effects of leptophos on rat brain levels and turnover rates of biogenic amines and their metabolites.

Leptophos is a potent acetylcholinesterase inhibitor which causes delayed central-peripheral neuropathy. Rats were administered multiple doses of leptophos until motor deficits were observed in rotorod performance in the highest dosage group. Doses lower than the median effective dose were then administered to other rats and alterations of brain catecholamine and serotonin levels and turnover rates were determined. Turnover rates of brain norepinephrine and dopamine were elevated in rats administered cumulative doses of 75 mg/kg leptophos over a 15-day period. Levels of the major dopamine metabolite, 3,4-dihydroxyphenylacetic acid, appeared to be slightly elevated at this dose level and levels of dopamine were also higher than controls. These observations suggest that leptophos increases brain adrenergic activity. Rats administered the same dose levels had significantly reduced serotonin turnover rates. This observation was possibly artifactual, because rats administered a cumulative dose of 225 mg/kg leptophos showed no difference from controls.

Methylmercury induced alterations in brain amine syntheses in rats.

Male Sprague-Dawley rats were treated with a cumulative dose of 0, 5, 15 and 50 mg methylmercury/kg body weight. The doses were adequate to provide a clinical neuromuscular dysfunction at the highest dose whereas no toxicity was observed at the lowest treatment level. Whole brain concentrations of tyrosine but not tryptophan were slightly reduced by the treatment. No effect of methylmercury was observed in the levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), or 5-hydroxyindoleacetic acid (5-HIAA). The synthesis rate for DA, but not the other biogenic amines, was decreased at all treatment levels of methylmercury. The results suggested a sensitivity of dopaminergic pathways to methylmercury toxicity in the central nervous system and are consistent with interference with cholinergic mechanisms and neurotransmitter enzymes by methylmercury as previously reported.