A survey of EPA/OPP and open literature data on selected pesticide chemicals tested for mutagenicity. I. Introduction and first ten chemicals.

Parties interested in registering a pesticide chemical with the U.S. Environmental Protection Agency's (USEPA's) Office of Pesticide Programs (OPP) must submit toxicity information to support the registration. Mutagenicity data are a part of the required information that must be submitted. This information is available to the public via Freedom of Information requests to the OPP. However, it is felt that this information would be more effectively and widely disseminated if presented in a published medium. Beginning with this publication, sets of mutagenicity data on pesticide chemicals will be periodically published in the Genetic Activity Profile (GAP) format. In addition, mutagenicity data extracted from the currently available open literature is also presented to provide a more complete database and to allow comparisons between the OPP-submitted data and other publicly available information.

Evaluation of the carcinogenic potential of pesticides. 4. Chloroalkylthiodicarboximide compounds with fungicidal activity.

The Health Effects Division of the Office of Pesticide Programs (OPP) assessed the carcinogenic potential of three structurally related chloroalkylthiodicarboximide fungicides using a consensus peer review process and EPA's 1986 guidelines for cancer risk assessment. All of the fungicides were categorized as Group B2 (probable human) carcinogens based upon findings of an increased incidence of malignant tumors, or combined malignant and benign tumors, in multiple experiments involving different strains of mice and rats. The primary sites of tumor formation with the chloroalkylthiodicarboximide fungicides in male and/or female mice (CD-1 and B6C3F1) were the gastrointestinal tract (captan, folpet, and captafol), the lymph system (folpet and captafol), and the vascular system (captafol). The main sites of tumor formation in rats of one or both sexes (CR CD, Wistar, or F344 strains) were the kidney (Captan and captafol), uterus (captan), mammary gland and liver (captafol). In addition, positive trends for thyroid, testicular, mammary gland, and lymph node tumors were observed with folpet in the same strains of rats. All three of the compounds exhibited positive mutagenic activity in a variety of in vitro short-term tests for gene mutation, DNA repair, and chromosomal aberrations in prokaryotic and eukaryotic cells, but were not genotoxic in available studies performed under in vivo conditions. The assessment of human cancer risk for captan, folpet, and captafol was made using low-dose extrapolation models.

Liver carcinogenesis by methyl carbamate in F344 rats and not in B6C3F1 mice.

Short-term and long-term carcinogenicity of methyl carbamate (MCB) was evaluated in F344 rats and B6C3F1 mice. In experiments lasting 6, 12, and 18 months, MCB was given in water by gavage to groups of 10 male and 10 female rats at 0 or 400 mg/kg body weight, 5 days per week, and to similar groups of mice at 0 or 1,000 mg/kg. At 6 months, MCB induced atypical mitoses, cytologic alterations, cytomegaly, pigmentation, necrosis, and neoplastic nodules of the liver in rats. At 12 and 18 months, carcinomas of the liver were induced by MCB in 80-90% of male rats and in 60-80% of female rats. None was observed in control rats or in mice. In the 2-year studies, MCB was given to groups of 50 male and 50 female rats at 0, 100, or 200 mg/kg and to similar groups of mice at 0, 500, or 1,000 mg/kg, 5 days/week. Chronic focal inflammation, cytologic alteration, hyperplasia, and neoplastic nodules and carcinomas (200 mg/kg groups only) of the liver were induced by MCB in rats. Liver tumor incidence data for combined experiments in rats were: males--5% in controls, 0% in 100 mg/kg group, 14% in 200 mg/kg group, and 77% in 400 mg/kg group; females--5% in controls, 0% in controls, 0% in 100 mg/kg group, 12% in 200 mg/kg group, and 63% in 400 mg/kg group. MCB was not shown to be carcinogenic in mice.

Characteristics of the U.S. EPA's Office of Pesticide Programs' toxicity information databases.

The United States Environmental Protection Agency's Office of Pesticide Programs (OPP) requires that data from toxicity testing be submitted to the OPP to support the registration of pesticide chemicals. Once the toxicity data are submitted, they are entered into various toxicity databases. The studies are listed in an archival database to catalog and allow retrieval of the study for review. Reviews of toxicity studies are then placed into a separate database that can be retrieved to support a regulatory position. Toxicity information for health effects other than cancer and gene mutations from chronic exposure is reviewed through a reference dose (RfD) approach, and these decisions and supporting data are entered into an RfD database. Carcinogenicity data are reviewed by a peer review process, and these decisions are entered into a newly developed database to show the regulatory decision with supporting data. The mutagenicity data are reviewed and acceptable data are entered into the Genetic Activity Profile system to catalog and display the submitted information. These databases contain the information used for hazard evaluations as part of the OPP review of pesticide chemicals.

Evaluation of the carcinogenic potential of pesticides. 3. Aliette.

Aliette, a fungicide compound, was evaluated for carcinogenic potential by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and EPA's guidelines for risk assessment. Aliette was categorized as a group C (possible human) carcinogen based upon evidence of an increased incidence of combined benign and malignant urinary bladder tumors in a single study involving male Charles River (CR) CD rats. The bladder tumors occurred only at the unusually high top dose level of aliette that was tested (40,000/30,000 ppm). The compound was not carcinogenic in female CR-CD rats in the same study, or in CD-1 mice of either sex in a second study. Monosodium phosphite, the main urinary metabolite of aliette, was also not carcinogenic in male or female CR-CD rats. Aliette was not demonstrated to be genotoxic. No structural analogues of aliette were identified. The mechanism of action for the production of bladder tumors was not identified; however, it did not appear to involve a genotoxic effect, a carcinogenic effect of metabolites, or the formation of renal stones. The data were not found to be sufficient to quantify human cancer risk from aliette.

Cocaine acts in the central nervous system to inhibit sympathetic neural activity.

Cocaine was administered i.v. to decerebrate cats while monitoring cardiac preganglionic sympathetic nerve activity (SNA), arterial blood pressure (BP) and heart rate (HR). Cocaine, 4 mg/kg i.v., reduced SNA by 55 +/- 6%, but did not significantly affect BP or HR. Cocaine, in doses that were ineffective by the i.v. route, was administered into the vertebral artery and produced decreases in SNA, BP and HR in anesthetized cats. Administration of cocaine into the carotid artery was without effect. Topical administration of cocaine to the intermediate area of the ventrolateral medullary surface (25 micrograms/side) evoked hypotension and bradycardia. Nisoxetine, an inhibitor of norepinephrine uptake, applied bilaterally to the intermediate area (30 micrograms/side) exerted a similar hypotensive effect. Lidocaine administered in doses equivalent to those of cocaine had no significant effect on SNA when given i.v. or on BP when given into the vertebral artery. These results indicate that cocaine inhibits central sympathetic outflow and that the site of action appears to be in the hindbrain at a site that is reached by placement of the drug at the intermediate area of the ventrolateral medulla. The data also indicate that the mechanism of action of cocaine to inhibit sympathetic outflow may be unrelated to its local anesthetic action and may involve inhibition of catecholamine uptake in the ventrolateral medulla.

Evaluation of the carcinogenic potential of pesticides. 2. Methidathion.

The carcinogen potential of methidathion, a dimethoxyorganic phosphorus pesticide and cholinesterase inhibitor, was evaluated by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and the EPA's guidelines for risk assessment. Methidathion was categorized as a Group C (possible human) carcinogen based upon evidence of an increased incidence of benign and malignant hepatocellular tumors, alone and in combination, in a single study involving male Chr-CD-1 mice. The compound was not carcinogenic in female Chr-CD-1 mice in the same study or in Sprague-Dawley rats of either sex in a second study. Methidathion was not genotoxic in a variety of in vitro or in vivo tests designed to detect DNA damage, chromosome aberrations, gene mutations, and sister chromatid exchange. Although methidathion was identified as being structurally similar to two other organophosphate insecticides, prothidathion and lythidathion, no toxicological data were available on either of these agents for comparative purposes. The biological information on methidathion was reviewed by the agency's FIFRA Scientific Advisory Panel who agreed with the category C designation for methidathion. The data were not found to be sufficient to quantify human risk to methidathion.

Evaluation of the carcinogenic potential of pesticides. 1. Acifluorfen.

The Health Effects Division of the Office of Pesticide Programs evaluates the carcinogenic properties of pesticides by a consensus peer review process in which all available biological information on a compound is evaluated according to EPA's guidelines for cancer risk assessment. In many cases, pesticides are also evaluated by an external group of accomplished scientists who comprise the Agency's Scientific Advisory Panel. The herbicide acifluorfen was evaluated by these processes and was classified as a Category B2 (probable human) carcinogen based upon evidence of an increased incidence of malignant, or combined benign and malignant, tumors in multiple experiments involving two different strains of mice. The compound produced benign and malignant liver tumors in male and female B6C3F1 mice and in female CD1 mice. Stomach papillomas were also observed in male and female B6C3F1 mice. Acifluorfen was mutagenic in bacteria and yeast, but not in mammalian cell systems. In addition, acifluorfen is structurally related to eight other diphenyl ether pesticides, all of which evoke liver tumours in mice or rats. The data were found to be sufficient to quantify human risk to acifluorfen.

Effect of activation of central nervous system serotonin 1A receptors on cardiorespiratory function.

Previous studies indicate that the new antihypertensive drug, urapidil, acts at the ventral surface of the medulla in cats to produce a fall in blood pressure. In addition, urapidil was found in receptor binding studies to have a relatively high affinity for the serotonin 1A receptor. These results suggest that drugs which bind to the serotonin 1A receptor might exert hypotensive effects at the ventral surface of the medulla (VSM). To test this hypothesis, the effects of 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT), the prototype drug for activating serotonin 1A receptors, were evaluated for cardiovascular activity after local application to the VSM. 8-OH-DPAT applied bilaterally to the intermediate area of the VSM in a dose of 1 micrograms/side produced a decrease in mean blood pressure of 60 +/- 7 mm Hg (P less than .05) and a decrease in heart rate of 26 +/- 4 beats/min (P less than .05) (n = 8). Increases in respiratory rate (8 +/- 1 breaths/1 min) and decreases in tidal volume (13 +/- 4 ml) also occurred. These changes were associated with a significant increase in respiratory minute volume (130 +/- 41 ml, P less than .05). Similar cardiorespiratory changes were produced by application of another drug with high affinity for the serotonin 1A receptor, namely B695-40, to the intermediate area of the VSM. Intravenous administration of 8-OH-DPAT in a dose of 100 micrograms/kg mimicked the cardiorespiratory effects of ventral surface application of this agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug interaction with gamma-aminobutyric acid/benzodiazepine receptors at the ventral surface of the medulla results in pronounced changes in cardiorespiratory activity.

Studies were carried out in chloralose-anesthetized cats while monitoring respiratory (tidal volume and respiratory rate) and cardiovascular (arterial pressure and heart rate) activity. Midazolam applied bilaterally to the intermediate area of the ventral surface of the medulla in doses of 0.75, 7.5 and 75 micrograms/side reduced tidal volume by -6 +/- 3, -10 +/- 1 and -11 +/- 1 ml, respectively. A dose of 250 micrograms/side produced apnea in each animal tested. Corresponding changes in arterial pressure were -35 +/- 9, -44 +/- 6, -43 +/- 9 and -64 +/- 17 mm Hg, respectively. Larger doses of chlordiazepoxide (e.g., 1000 micrograms/side) were required to produce similar effects. Intravenous administration of midazolam in doses of 1.5 to 150 micrograms had no significant effect on cardiorespiratory activity. However, larger doses of midazolam given i.v. produced cardiorespiratory depression that was similar to that observed with centrally applied drug. Pretreatment or treatment with centrally applied flumazenil or bicuculline counteracted the cardiorespiratory effects of centrally applied midazolam. Most importantly, ventral surface application of flumazenil counteracted the cardiorespiratory depressant effects of i.v. midazolam. Central administration of ethyl-beta-carboline-3-carboxylate produced cardiorespiratory effects opposite to those seen with midazolam, and these stimulatory effects were also counteracted by centrally applied flumazenil. These results indicate that alterations in cardiorespiratory activity can be produced by drugs interacting with gamma-aminobutyric acid/benzodiazepine receptors at the ventral surface of the medulla.

Cardiorespiratory effects produced by activation of cholinergic muscarinic receptors on the ventral surface of the medulla.

Our purpose was to examine the influence of inhibition of cholinesterase at the ventral surface of the medulla on cardiorespiratory activity in the chloralose-anesthetized cat. Administration of the anticholinesterase agent, diisopropylfluorophosphate (DFP) to areas responding to acetylcholine (i.e., rostral and caudal chemosensitive areas of the ventral surface of the medulla) in doses ranging from 12.5 to 50 micrograms bilaterally had minimal effects on cardiorespiratory activity. However, similar doses applied to the intermediate area of the ventral surface of the medulla produced an increase in tidal volume and hypotension. For example, a dose of 12.5 micrograms increased tidal volume by 14 +/- 3 ml (P greater than .05). Similar responses were seen with higher doses of DFP; in addition, respiratory depression (apnea) also occurred. This depression was characterized by a slowing in respiratory rate. The organophosphate compound, soman, in doses of 0.25 and 0.5 micrograms produced effects similar to those seen with DFP with the exception that an increase in respiratory rate was observed before the decrease in respiratory rate occurred. In addition, a greater degree of hypotension was observed with soman as compared to DFP. Findings comparable to those obtained with DFP were produced by the muscarinic receptor agonist, oxotremorine (0.077-10 micrograms). The effects of DFP, soman and oxotremorine were counteracted by locally applied atropine. In addition, measurements of acetylcholinesterase activity taken from the rostral, intermediate and caudal areas indicate a relatively low activity at the rostral area but a relatively high activity at the intermediate area.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental studies on the neurocardiovascular effects of urapidil.

The major purpose of our study was to determine whether urapidil acts in the central nervous system (CNS) to lower arterial blood pressure. Once demonstrating a CNS antihypertensive action of urapidil we further set out to determine: (1) the relative role of a CNS antihypertensive action to the total antihypertensive effect of urapidil; (2) the brain site of action for the antihypertensive effect of urapidil; and, (3) the receptor mechanism whereby urapidil acts in the CNS to lower arterial blood pressure. Studies were conducted in chloralose-anaesthetised cats, and arterial blood pressure and heart rate were monitored. Drugs were administered intravenously (IV), into the cerebral ventricles (ICV), topically by application to the ventral surface of the medulla and by microinjection into specific nuclei. Receptor binding studies were also conducted using rat cerebral cortex homogenates. We found that injection of urapidil into the fourth ventricle decreased arterial pressure. Local application of urapidil to the ventral medullary surface also decreased arterial blood pressure. Microinjection of urapidil into one of the nuclei associated with the ventral surface of the medulla, the rostral part of the nucleus reticularis lateralis (rLRN), produced a similar degree of antihypertensive effect. The effect of urapidil was not altered by alpha 1-receptor blockade. Instead, the urapidil effect resembled that produced by drugs that stimulate serotonin (5-hydroxytryptamine)-1A receptors (B695-40 and 8-OH-DPAT). Furthermore, urapidil was found to have the highest potency for binding to serotonin-1A receptor sites (as compared to alpha 1- and alpha 2-receptor sites). Urapidil administered IV was shown to lower arterial blood pressure in part by blocking peripheral alpha 1-adrenoceptors but also, in high doses, by acting in the CNS to decrease central sympathetic outflow. These data indicate that urapidil is a unique drug, possessing both peripheral and CNS actions which contribute to its antihypertensive effect. Urapidil may also be unique in that its central action may involve activation of serotonin-1A receptors.

Respiratory depressant effects of GABA alpha- and beta-receptor agonists in the cat.

The aim of this study was to evaluate the cardiorespiratory effects of intravenously administered gamma-aminobutyric acid (GABA) alpha-(4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, THIP) and beta-(baclofen) receptor agonists and to locate the site of action of these drugs in the brain. THIP and baclofen were administered to alpha-chloralose-anesthetized cats while minute ventilation (VE), arterial blood pressure (AP), and heart rate were monitored. THIP, in doses of 0.5 to 2 mg/kg decreased VE, tidal volume (VT), and AP. No changes in respiratory rate (f) or inspiratory (TI) or expiratory (TE) duration were observed. Baclofen, in doses of 0.5 to 4 mg/kg, decreased VE, f, and AP. VT and TI increased and an "apneustic" breathing pattern was seen. THIP (9.5 micrograms), applied bilaterally to the glycine-sensitive area of the ventral medulla, reproduced the effects seen with intravenous administration. Application of 10 micrograms of bicuculline bilaterally to this area reversed the effects of intravenous THIP but not those of baclofen. Baclofen (5.6-56 micrograms), administered by the intracisternal route, produced the same respiratory effects seen with intravenous administration. We conclude that activation of GABA alpha- and beta-receptors produces cardiorespiratory depression. However, this is accomplished by different mechanisms and by actions exerted at different central nervous system sites.

Thirteen-week oral toxicity study of methyl carbamate in rats and mice.

The purpose of this study was to identify the toxicologic effects produced by methyl carbamate in F344 rats and B6C3F1 mice. Administration of methyl carbamate by gavage five times a week for 13 weeks to male (50, 100, 200, 400, or 800 mg/kg) and female (62.5, 125, 250, 500, or 1000 mg/kg) rats resulted in dose-related lesions in the liver characterized by proliferative changes in hepatocytes consisting of foci of cellular alteration and frequent mitoses with atypical forms. Toxic alterations consisted of focal hepatocellular necrosis, pigmentation of Kupffer's cells, and the presence of basophilic inclusions resembling nucleoli in the cytoplasm of hepatocytes. Other toxic effects observed in rats were weight loss, testicular hypoplasia, bone marrow hyperplasia, and excessive pigmentation of the spleen. The survival of male and female rats was reduced following administration of the highest dose of methyl carbamate. In contrast to these findings, administration of the chemical to male (93.75, 187.5, 375, 750, or 1500 mg/kg) and female (125, 250, 500, 1000, or 2000 mg/kg) mice five times a week for 13 weeks resulted only in weight loss and inflammatory changes of the liver. The proliferative nature of the hepatic lesions observed in rats suggests that the compound is potentially hepatocarcinogenic.

Hypotensive effect of urapidil: CNS site and relative contribution.

The purposes of our study were to determine the contribution of the CNS to the hypotensive effect of urapidil in the cat and the specific brain site of action of this agent. For the first purpose, urapidil was studied on preganglionic sympathetic nerve activity, arterial pressure, and heart rate. Three systemic bolus doses of urapidil were administered (0.22, 0.44, and 1.3 mg/kg). All three doses lowered arterial pressure, and the highest dose produced a significant decrease in sympathetic nerve discharge in five of six animals studied. The lower two doses had no significant effect on sympathetic activity, and none of the doses altered heart rate. These results suggest that a high i.v. dose of urapidil is required to evoke hypotension by an action in the central nervous system (CNS). For the second purpose, urapidil was applied bilaterally to the intermediate area of the ventral surface of the medulla in doses of 25 and 50 micrograms. These doses caused decreases in arterial pressure of -6.1 +/- 2.2 (p less than 0.05) and -21.0 +/- 5.9 (p less than 0.05) mm Hg, respectively, but no change in heart rate. In addition, respiratory stimulation also occurred with the higher dose as respiratory minute volume increased by 81 +/- 14 ml/min (p less than 0.05). The highest dose of urapidil had no effect on arterial pressure when applied to other chemosensitive areas of the ventral surface of the brain. Comparative studies with prazosin (10 micrograms applied bilaterally to the intermediate area) indicated no hypotensive effect of this alpha 1-adrenoceptor blocking agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical stimulation of the area postrema induces cardiorespiratory changes in the cat.

The purpose of our study was to determine the cardiorespiratory effects of exciting cell bodies of the area postrema of the cat. This was accomplished by local application of L-glutamic acid (bilateral application of 5 microliter of a 250-1000 mM solution) and kainic acid (bilateral application of 5 microliter of a 40 mM solution) to the area postrema of chloralose-anesthetized cats while monitoring arterial pressure, heart rate, tidal volume and respiratory rate. These excitatory amino acids activate neuronal cell bodies but not axons of passage. L-Glutamic acid produced a dose-dependent increase in arterial pressure, decreases in respiratory rate and minute volume and, occasionally, ventricular tachyarrhythmias. Kainic acid produced effects similar to those seen with L-glutamic acid except the changes in respiratory activity were more pronounced with each animal exhibiting respiratory arrest. In artificially respired animals, kainic acid produced similar cardiovascular changes as those occurring in spontaneously breathing animals (i.e. increases in arterial pressure of 61 +/- 5.7 mm Hg, and in heart rate of 32 +/- 8.3 beats/min). Finally, application of kainic acid to the area postrema abolished the pressor and tachycardic responses to bilateral occlusion of the carotid arteries. These results suggest that activation of cell bodies in the area postrema can result in pronounced cardiorespiratory changes.

Mechanism of the antihypertensive effect of alpha 2-agonists.

Drugs such as clonidine, methyldopa, guanabenz, guanfacine, and lofexidine have their primary site of antihypertensive action in the central nervous system (CNS) to activate alpha 2-adrenergic receptors and lower arterial pressure. The most probable CNS site of action of these drugs is the medulla oblongata at a post-synaptic location. Current evidence indicates that within the medulla, the prototype drug, clonidine, most likely acts at the lateral reticular nucleus. This site is the most sensitive in terms of hypotension occurring after microinjection of clonidine. In addition, lesion of this nucleus abolishes the hypotensive effect of systemically administered clonidine. Recently, a clonidine-displacing endogenous brain substance has been isolated and partially purified from calf brain. Knowledge of where clonidine acts to lower blood pressure should help in assessing the role of an endogenous clonidine-displacing substance in CNS control of cardiovascular function.

Two-year inhalation toxicity study of propylene in F344/N rats and B6C3F1 mice.

Chronic toxicity studies of propylene were conducted by exposing groups of 50 F344/N rats and 50 B6C3F1 mice of each sex in chambers to air containing the chemical in concentrations of 5000 and 10,000 ppm, 6 hr per day, 5 days per week, for 103 weeks. Groups of 50 rats and 50 mice of each sex in similar chambers received clean air only on the same schedule and served as controls. Survival and mean body weights of exposed and control male and female rats and mice were similar. In exposed rats, increased incidences of nonneoplastic lesions were observed in the nasal cavity. These consisted of epithelial hyperplasia in female rats exposed to the high concentration, and squamous metaplasia in female rats exposed to both concentrations and in male rats exposed to the low concentration. In addition, inflammatory changes characterized by an influx of lymphocytes, macrophages, and granulocytes into the submucosa and by granulocytes into the lumen occurred in male rats of both exposure groups. There was no evidence of nasal cavity lesions in exposed mice, suggesting a species difference in sensory irritation to propylene. There were no treatment-related increases or decreases in tumor incidence in the exposed groups relative to controls for either rats or mice. These data suggest that inhaled propylene induces signs of nasal cavity toxicity in rats but not in mice, and that the chemical is not carcinogenic to either species at the concentrations tested.

Blockade of bicuculline-induced pressor and tachycardic responses by forebrain administration of muscimol.

To determine whether i.v. administered bicuculline acts in the forebrain to increase arterial blood pressure and heart rate, this agent was administered i.v. to chloralose anesthetized cats that had muscimol injected into and restricted to the forebrain ventricles. Bicuculline (0.5 mg/kg i.v.) given alone increased arterial pressure by 56 +/- 8 mm Hg and heart rate by 45 +/- 11 beats/min. Bicuculline given to animals exposed to muscimol exhibited no increase in either of these parameters. Muscimol localized to the forebrain did not alter the pressor response to a non-GABA antagonist agent, strychnine, indicating a specific interaction of the drugs with GABA receptors in the forebrain.