Acetaminophen predisposes to renal and hepatic injury from compound A in the fasting rat

Results of previous studies of Compound A, a degradation product of sevoflurane, suggested that decreases in glutathione stores may increase potential Compound A nephrotoxicity. By depleting these stores, fasting and various drugs may augment such nephrotoxicity. To test this possibility, we pretreated fasted Fisher rats with intraperitoneal 0 (vehicle only), 250, 500, or 1000 mg/kg of acetaminophen, a commonly used drug that depletes glutathione stores. After pretreatment, we administered Compound A for 3 h at concentrations ranging from 0 to 200 ppm. The larger doses of acetaminophen predisposed to greater renal and hepatic injury. For example, at 100 ppm Compound A, no rats had renal cortical injury when given vehicle only or 250 mg/kg acetaminophen, but 90% (9 of 10 rats) had injury at 500 mg/kg and 100% (13 of 13) at 1000 mg/kg. Similarly, at 100 ppm Compound A, hepatic injury was not evident with vehicle only or 250 mg/kg, but occurred in 30% of rats at 500 mg/kg, and in 69% at 1000 mg/kg. Given the considerable differences between humans and rats, and given the large doses of acetaminophen required, the clinical relevance of these findings is unclear. If clinically relevant, circumstances producing glutathione depletion (e.g., ingestion of drugs such as acetaminophen, or nutritional deficiencies) may predispose to renal or hepatic injury from Compound A in patients given sevoflurane at low fresh gas flow rates.

In vivo testing of crosslinked polyethers. II. Weight loss, IR analysis, and swelling behavior after implantation

As reported in Part I ("In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation," J. Biomed. Mater. Res., this issue, pp. 307-320), microscopical evaluation after implantation of crosslinked (co)polyethers in rats showed differences in the rate of biodegradation, depending on the presence of tertiary hydrogen atoms in the main chain and the hydrophilicity of the polyether system. In this article (Part II) the biostability will be discussed in terms of weight loss, the swelling behavior, and changes in the chemical structure of the crosslinked polyethers after implantation. The biostability increased in the order poly(POx) < poly(THF-co-OX) < poly(THF) for the relatively hydrophobic polyethers. This confirmed our hypothesis that the absence of tertiary hydrogen atoms would improve the biostability. On the other hand, signs of biodegradation were observed for all polyether system studied. Infrared surface analysis showed that biodegradation was triggered by oxidative attack on the polymeric chain, leading to the formation of carboxylic ester and acid groups. It also was found that in the THF-based (co)polyethers, alpha-methylene groups were more sensitive than beta-methylene groups. For a hydrophilic poly(THF)/PEO blend, an increase in surface PEO content was found, which might be due to preferential degradation of the PEO domains.

In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation

The in vivo biocompatibility and biodegradation of cross-linked (co)polyethers with and without tertiary hydrogen atoms in the main chain and differing in hydrophilicity were studied by means of subcutaneous implantation in rats. After 4 days, 1 month, and 3 months postimplantation, the tissue reactions and interactions were evaluated by light microscopy (LM) and transmission electron microscopy (TEM). Poly(tetrahydrofuran) (poly(THF)), poly(propylene oxide) (poly(POx)), and poly(tetrahydrofuran-co-oxetane) (poly-(THF-co-OX)) were tested as relatively hydrophobic polyethers, and poly(ethylene oxide) (PEO) and a poly(THF)/ PEO blend were used as more hydrophilic materials. In general, all polyethers showed good biocompatibility with respect to tissue reactions and interactions, with low neutrophil and macrophage infiltration, a quiet giant cell reaction, and formation of a thin fibrous capsule. For the relatively hydrophobic polyethers studied, the biostability increased in the order poly(POx) < poly(THF-co-OX) < poly(THF), probably indicating that the absence of tertiary hydrogen atoms has a positive effect on the biostability. Concerning the more hydrophilic materials, crosslinked PEO showed the highest rate of degradation, probably due to the mechanical weakness of the hydrogel in combination with the highest presence of giant cells as a result of the high porosity. A frayed surface morphology was observed after implantation of the crosslinked poly(THF)/PEO blend, which might be due to preferential degradation of PEO domains.

Subchronic and developmental toxicity studies of vaporized diisopropyl ether in rats

Two inhalation studies were performed with a vaporized sample of commercial-grade diisopropyl ether (DIPE). In the subchronic study, Sprague-Dawley rats (14/sex) were exposed to 0 (both untreated and sham-exposed controls), 480, 3300, or 7100 ppm DIPE for 6 h/d, 5 d/wk, for approximately 90 d. DIPE itself accounted for 91-95% of the vapors, with the remainder being a mixture of 27-29 compounds. Exposure to DIPE did not adversely affect clinical signs, body weight, serum chemistry, hematology, or the number of sperm or spermatids. Exposure of males to 7100 ppm resulted in hypertrophy of liver cells associated with increased liver weight and in increased kidney weight with an increased incidence of hyaline droplets in proximal tubules of the kidney. Females had increased weight of both liver and kidney, although kidney increased only in relation to sham-exposed controls and no morphological changes were observed in either organ. At 3300 ppm, weights of liver and kidney were again increased in males; the liver weights were increased in females only compared to sham-exposed controls and not untreated controls. No abnormalities were observed morphologically. No changes were observed with 480 ppm. In the developmental toxicity study, pregnant Sprague-Dawley rats (22/group) were exposed to 0 (both untreated and sham-exposed controls), 430, 3095, or 6745 ppm for 6 h/d on gestation d 6-15. Animals were sacrificed on gestation d 20. With 6745 ppm, dams had a slight reduction in body weight gain and a significant decrease in food consumption. A concentration-related increase in the incidence of rudimentary 14th ribs was observed, but its significance was uncertain. There was no apparent toxicity, either maternal or fetal, at the lowest exposure concentration. Both studies indicated a low order of toxicity for DIPE.

Desflurane, sevoflurane, and isoflurane impair canine left ventricular-arterial coupling and mechanical efficiency

BACKGROUND

The effects of desflurane, sevoflurane, and isoflurane on left ventricular-arterial coupling and mechanical efficiency were examined and compared in acutely instrumented dogs.

METHODS

Twenty-four open-chest, barbiturate-anesthetized dogs were instrumented for measurement of aortic and left ventricular (LV) pressure (micromanometer-tipped catheter), dP/dtmax, and LV volume (conductance catheter). Myocardial contractility was assessed with the end-systolic pressure-volume relation (Ees) and preload recruitable stroke work (Msw) generated from a series of LV pressure-volume diagrams. Left ventricular-arterial coupling and mechanical efficiency were determined by the ratio of Ees to effective arterial elastance (Ea; the ratio of end-systolic arterial pressure to stroke volume) and the ratio of stroke work (SW) to pressure-volume area (PVA), respectively.

RESULTS

Desflurane, sevoflurane, and isoflurane reduced heart rate, mean arterial pressure, and left ventricular systolic pressure. All three anesthetics caused similar decreases in myocardial contractility and left ventricular afterload, as indicated by reductions in Ees, Msw, and dP/dtmax and Ea, respectively. Despite causing simultaneous declines in Ees and Ea, desflurane decreased Ees/Ea (1.02 +/- 0.16 during control to 0.62 +/- 0.14 at 1.2 minimum alveolar concentration) and SW/PVA (0.51 +/- 0.04 during control to 0.43 +/- 0.05 at 1.2 minimum alveolar concentration). Similar results were observed with sevoflurane and isoflurane.

CONCLUSIONS

The present findings indicate that volatile anesthetics preserve optimum left ventricular-arterial coupling and efficiency at low anesthetic concentrations (< 0.9 minimum alveolar concentration); however, mechanical matching of energy transfer from the left ventricle to the arterial circulation degenerates at higher end-tidal concentrations. These detrimental alterations in left ventricular-arterial coupling produced by desflurane, sevoflurane, and isoflurane contribute to reductions in overall cardiac performance observed with these agents in vivo.

Safety evaluation of perfluoropolyethers, liquid polymers used in barrier creams and other skin-care products

Fomblin HC products are a 'family' of high-purity perfluoropolyethers manufactured for barrier cream and other personal care applications which involve direct application to the skin. To confirm the safety of such use, representative Fomblin HC products were tested in experimental animals for acute toxicity, primary and repeated insult irritancy, sensitization and photosensitization, subacute oral toxicity and comedogenicity; mutagenicity was examined in vitro, and irritancy or sensitization was also investigated on human skin (in patch tests with volunteers). A high molecular weight Fomblin HC only was tested in rats for subacute oral toxicity and in man for dermal effects. Single oral doses of 15 g/kg body weight were without evident toxicity to rats, as were single dermal applications or an ip injection at 5 g/kg. No primary irritant action was seen in rabbits or man, and similarly there was no evidence of skin sensitization or photosensitization in guinea pigs, or sensitization in man. No mutagenic action on Salmonella strains of tester bacteria was seen. In repeat dose irritancy or oral toxicity tests in rabbits or rats, no adverse effects of Fomblin HC products were noted; in particular, daily oral administration (1000 mg/kg/day) to rats over 28 days produced no significant reaction. No comedogenic action was found. From the known chemistry of the perfluoropolyethers, the test programme reported here and the limited published data, it is concluded that the intended use of Fomblin HC products in formulations applied to human skin has a high margin of safety.

Increased [3H]phorbol ester binding in rat cerebellar granule cells and inhibition of 45Ca2+ sequestration in rat cerebellum by polychlorinated diphenyl ether congeners and analogs: structure-activity relationships

Our previous reports indicate that ortho-substituted non-coplanar polychlorinated biphenyl (PCB) congeners perturbed neuronal Ca2+-homeostasis in vitro, altered agonist-stimulated inositol phosphate accumulation, and caused protein kinase C (PKC) translocation. The structure-activity relationship (SAR) with 24 PCB congeners was consistent with a chlorination pattern that favored non-coplanarity while those with chlorination that favored coplanarity were less active. To test the hypothesis that coplanarity (or lack thereof) is a significant factor in the activity of PCBs, studies with related classes of chemicals such as the polychlorinated diphenyl ethers (PCDEs), in which coplanarity is more difficult to achieve regardless of degree and pattern of chlorination, were initiated. The selected PCDEs and their analogs are predicted to be active, since they are non-coplanar in nature. The effects of these chemicals were studied using the same measures for which PCBs had differential effects based on structural configuration. These measures include PKC translocation as determined by [3H]-phorbol ester ([3H]PDBu) binding in cerebellar granule cells and 45Ca2+ sequestration as determined by 45Ca2+ uptake by microsomes and mitochondria isolated from adult rat cerebellum. All the PCDE congeners studied, increased [3H]PDBu binding in a concentration-dependent manner. The order of potency was 2,4,4'-trichlorodiphenyl ether > 4,4'-dichlorodiphenyl ether > diphenyl ether, 3,3',4,4'-tetrachlorodiphenyl ether and, 2,2',4,4',5- and 2,3',4,4',5-pentachlorodiphenyl ethers. The structurally related diphenyl ether nitrofen and diphenyl ethanes o,p'-1,1,1-trichloro-2,2-bis[p-chlorophenyl]ethane (DDT) and p,p'-DDT increased [3H]PDBu binding to a similar extent (28-35% stimulation at 100 microM). All PCDE congeners and their analogs inhibited 45Ca2+ sequestration by microsomes and mitochondria. Of all the chemicals, unchlorinated diphenyl ether was the least active. These results are in agreement with previous SAR findings in which non-coplanar PCBs are active and support our hypothesis that the extent of coplanarity determined by a pattern of chlorination on certain aromatic hydrocarbons can weaken their potency in vitro, although the extent of chlorination is also important.

Metabolism of compound A by renal cysteine-S-conjugate beta-lyase is not the mechanism of compound A-induced renal injury in the rat

Compound A [CF2 = C(CF3)OCH2F], a vinyl ether produced by CO2 absorbents acting on sevoflurane, can produce corticomedullary junction necrosis (injury to the outer stripe of the outer medullary layer, i.e., corticomedullary junction) in rats. Several halogenated alkenes produce a histologically similar corticomedullary necrosis by converting glutathione conjugates of these alkenes to halothionoacetyl halides. To test whether this mechanism explained the nephrotoxicity of Compound A, we blocked three metabolic steps which would lead to formation of a halothionoacetyl halide: 1) we depleted glutathione by administering dl-buthionine-S, R-sulfoximine (BSO); 2) we blocked cysteine S-conjugate formation by administering acivicin (AT-125); and 3) we inhibited subsequent metabolism by renal cysteine conjugate beta-lyase to the nephrotoxic halothionoacetyl halides by administering aminooxyacetic acid (AOAA). These treatments were given alone or in combination to separate groups of 10 or 20 Wistar rats before their exposure to Compound A. We hypothesized that blocking these metabolic steps should decrease the injury produced by breathing 150 ppm of Compound A for 3 h. However, we found either no change or an increase in renal injury, suggesting that this pathway mediates detoxification rather than toxicity. Our findings suggest that the cysteine-S-conjugate-mediated pathway is not the mechanism of Compound A nephrotoxicity and, therefore, observed interspecies differences in the activity of this activating pathway may not be relevant in the prediction of the nephrotoxic potential of Compound A in clinical practice.

Identification in rat bile of glutathione conjugates of fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether, a nephrotoxic degradate of the anesthetic agent sevoflurane

Recent studies have indicated that the nephrotoxicity of fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether ("Compound A"), a breakdown product of the inhaled anesthetic sevoflurane, may be mediated by a reactive intermediate(s) generated via the cysteine conjugate beta-lyase pathway. In order to gain a better understanding of glutathione (GSH)-dependent metabolism of Compound A, the present study was carried out with the primary goal of detecting and characterizing Compound A--GSH conjugates. By means of ionspray LC-MS/MS and NMR spectroscopy, a total of four GSH conjugates ("A1-A4") were identified from the bile of rats dosed intraperitoneally with Compound A. A1 and A2 were identified as two diastereomers of S-[1,1-difluoro-2-(fluoromethoxy)-2-(trifluoromethyl)ethyl]glutath ione, while A3 and A4 were identified as (E)- and (Z)-S-[1-fluoro-2-(fluoromethoxy)-2-(trifluoromethyl)-vinyl]glutat hione, respectively. Quantitative analyses indicated that approximately 29% of the administered dose of Compound A was excreted into the bile in the form of the above GSH conjugates over a period of 6 h. Studies conducted in vitro demonstrated that the reaction of Compound A with GSH was catalyzed by both rat liver cytosolic and microsomal glutathione S-transferases (GST), with the two enzyme systems exhibiting different product selectivities. Formation of these GSH conjugates also occurred nonenzymatically at an appreciable rate. These results indicate that spontaneous and enzyme-mediated conjugation with GSH represents a major pathway of metabolism of Compound A in rats. Conjugation of Compound A with GSH in vivo appeared to be catalyzed preferentially by microsomal rather than cytosolic GST, based on comparison of biliary, microsomal, and cytosolic metabolic profiles. By analogy with other haloalkenes, further metabolism of the corresponding cysteine conjugates of Compound A by renal cysteine conjugate beta-lyase may lead to the formation of reactive acylating agents, which would be expected to bind covalently to cellular macromolecules and cause organ-selective nephrotoxicity.

[Nephrotoxicity and fluoride from the viewpoint of the nephrologist]

Fluoride released from methoxyflurane (MOF) during its hepatic and extrahepatic metabolism has been regarded as the major culprit responsible for MOF-induced nephrotoxicity. In the isolated, perfused rat kidney model, admixture of 1500 mumol/l fluoride to the perfusate resulted in tubular and glomerular damage with concomitant anuria. Fluoride administration in Fischer 344 rats in vivo elicited a renal diabetes insipidus-like syndrome that had also been observed in patients after MOF anaesthesia. The renal concentrating defect is most probably due to both dissipation of the corticomedullary osmolality gradient in the interstitium and failure of water reabsorption due to ADH refractoriness of the distal tubular cells. Hypothetically, the underlying mechanism may be a fluoride-induced inhibition of enzymes involved in intracellular energy production such as ATPase or enolase. The degree of nephrotoxicity correlates loosely with maximal serum fluoride levels, but can probably be modulated by further factors like intrarenal in situ formation of fluoride, urinary pH and flow, and especially, the presence of other nephrotoxins. This mitigates the importance of maximal fluoride serum levels, especially the 50 mumol threshold, as predictors of clinically relevant nephrotoxicity. To date, no nephrotoxic effects of sevoflurane could be demonstrated.

[Fluoride-induced nephrotoxicity: factor fiction?]

In the 1960s, the widespread use of the inhalational anaesthetic methoxyflurane was associated with a significant occurrence of postoperative renal dysfunction. This was attributed to hepatic biotransformation of methoxyflurane and subsequent release of inorganic fluoride ions into the circulation. Based upon the clinical experience with methoxyflurane, serum fluoride concentrations exceeding 50 mumol/l were considered to be nephrotoxic. Without further reevaluation, this 50 mumol/l threshold was subsequently applied to other fluorinated anaesthetics as well. Enflurane and even isoflurane may, when used during prolonged operations, also yield anorganic fluoride levels in excess of 50 mumol/l. Nevertheless, no cases of renal dysfunction attributable to prolonged use of these anesthetics have been reported. About 4% of the new inhalational anaesthetic sevoflurane is metabolized, and fluoride concentrations exceeding those after enflurane are frequently measured. Numerous studies have examined the nephrotoxic potential of sevoflurane degradation products. However, fluoride-related toxicity has been observed neither in animal nor in clinical studies, including prolonged administration and patients with pre-existing renal disease. New insights into the intrarenal metabolisation of volatile anaesthetics may well explain the absence of nephrotoxicity after sevoflurane. The threshold for fluoride nephrotoxicity of 50 mumol/l, still given in many medical text-books, can no longer be applied as an indicator of nephrotoxicity after isoflurane, enflurane or sevoflurane. Therefore, the elevated serum fluoride concentrations consistently recorded following anaesthesia with sevoflurane are devoid of clinical significance.

[Toxicology and clinical significance of base-catalized degradation of sevoflurane to Compound A]

Sevoflurane breaks down in basic environments to form a vinyl ether known as Compound A. This compound is toxic in the rat, with an LC50 of about 400 ppm after 3 h exposure and with renal damage evident between 50 and 100 ppm. There is no valid current evidence that Compound A is toxic in man, and the rat may not be an appropriate model for determination of this breakdown product's toxic potential in humans. The main factors influencing the degree of patient exposure to Compound A include fresh gas flow, sevoflurane concentrations, absorber temperature and composition, and the patient's carbon dioxide production.

[The cardiovascular effects of sevoflurane]

The cardiovascular effects of sevoflurane as published from clinical and experimental studies are reviewed with respect to general haemodynamics and organ perfusion. Sevoflurane appears to be quite similar to isoflurane, with some minor exceptions. In adult patients and volunteers, sevoflurane has not been associated with increases in heart rate, whereas isoflurane and desflurane caused significant increases in heart rate at higher concentrations. The coronary vasodilatory potency of sevoflurane appears to be lower than that of isoflurane, and sevoflurane has not been associated with a reduction of blood flow to collateral-dependent myocardium in dogs with steal-prone anatomy. In several multi-center studies where patients with coronary artery disease or at high risk for coronary artery disease were randomised to receive either sevoflurane or isoflurane for cardiac or non-cardiac surgery, the incidence of myocardial ischaemia and infarction did not differ between treatment groups. In both human and animal models, sevoflurane preserves cerebral blood flow and reduces cerebral metabolic rate much like isoflurane. Considering its favourable pharmacokinetic properties, the introduction of sevoflurane into clinical practice appears to be a promising extension of the anaesthetic spectrum.

Toxicokinetics and acute effects of MTBE and ETBE in male volunteers

Methyl tertiary butyl ether (MTBE) is widely used in gasoline as an oxygenator and octane enhancer. There is also an interest in using the ethyl tertiary butyl (ETBE) and methyl tertiary amyl (TAME) ethers. We measured the blood, water, and olive oil/air partition coefficients in vitro of MTBE, ETBE, TAME and tertiary butyl alcohol (TBA), a metabolite of MTBE and ETBE. The results indicate similar uptake and distribution behavior for the three ethers and a slight affinity for fatty tissues. The partition coefficients of TBA indicate that this metabolite is not excreted via the lungs to any great extent and that it is preferentially distributed in body water. Further, we exposed 10 healthy male volunteers to MTBE vapor at 5, 25 and 50 ppm for 2 h during light physical exercise. Uptake and disposition were studied by measuring MTBE and TBA in inhaled and exhaled air, blood and urine. Low uptake, high post-exposure exhalation, and low blood clearance indicate slow metabolism of MTBE relative to many other solvents. A low recovery of TBA in urine (below 1% of uptake) indicates further metabolism of TBA. The concentration of MTBE and TBA in blood was proportional to exposure level suggesting linear kinetics up to 50 ppm. The half life of 7-10 h in blood and urine indicates that TBA would be more suitable than the parent compound as a biomarker for MTBE exposure. Subjective ratings (discomfort, irritative symptoms, CNS effects) and eye (redness, tear film break-up time, conjunctival damage, blinking frequency) and nose (peak expiratory flow, acoustic rhinometry, inflammatory markers in nasal lavage) measurements indicated no or minimal effects of MTBE.

Health effects of inhaled tertiary amyl methyl ether and ethyl tertiary butyl ether

Government specifications on the oxygen content of motor gasoline sold in certain areas of the USA have resulted in commercialization of the oxygenate fuel additives tertiary amyl methyl ether (TAME) and ethyl tertiary butyl ether (ETBE). TAME and ETBE were evaluated in 4-week rat inhalation studies sponsored by Amoco Corporation. Target vapor concentrations were 0, 500, 2000, or 4000 ppm for 6 h per day, 5 days per week, for 4 weeks. TAME exposure at 4000 ppm resulted in 25% mortality, apparently as a consequence of severe CNS depression. Body weight gain was decreased in the TAME high dose male rats. In contrast, no ETBE exposed animals died during the study and no changes in body weight gain were observed. Significant effects on functional observational battery (FOB) parameters were only found in the TAME high and mid-dose groups immediately after exposure. All affected FOB parameters were normal by the next day. Both TAME and ETBE exposures significantly increased relative liver weights in the high and mid-dose groups. However, no treatment-related histopathologic findings were noted for either compound. Clinical chemistry and hematology findings were absent with ETBE exposure and minimal with TAME exposure. The results indicate that 500 ppm was a NOAEL for both compounds in these studies.

Inhalation toxicity study of a haloalkene degradant of sevoflurane, Compound A (PIFE), in Sprague-Dawley rats

BACKGROUND

Under certain circumstances in the clinical setting, contact of the anesthetic sevoflurane with a CO2 absorbent (e.g., soda lime, Baralyme) leads to the formation of a degradant designated as pentafluoroisopropenyl fluoromethyl ether (PIFE; Compound A). Previous studies have shown that the kidney is the primary target organ for toxicity in the rat. This study was designed to determine the impact of PIFE on rat renal histology correlated with functional changes. The findings are discussed in terms of probable mechanism of action and relevance to humans.

METHODS

Male and female Sprague-Dawley rats were exposed to 0, 30, 61, 114, or 202 ppm PIFE for a single 3-h period via nose-only inhalation. Rats were observed daily for behavioral changes or external physical signs of toxicity (i.e., lacrimation, dyspnea, piloerection, etc.) and body weights were recorded at 6, 4, and 1 day preexposure and 1, 3, 7, and 13 days postexposure. Animals were evaluated for hematologic, clinical chemistry and/or urinalysis changes immediately postexposure and/or at 1, 4, and 14 days postexposure. Rats were killed, subjected to a macroscopic postmortem examination, and evaluated for histopathologic changes in all major tissues and organs at 1, 4, and 14 days postexposure.

RESULTS

Labored breathing was observed in 3 of the 20 and 2 of the 20 rats in the 114 ppm and 202 ppm groups, respectively, during the 3-h exposure period. No significant reductions in body weight gain were noted during the 2-week study period. Clinical chemistry evaluations revealed increases in blood urea nitrogen and creatinine 1 day postexposure in males and females exposed to 202 ppm PIFE. Changes in urinary glucose, protein and N-acetyl-beta-glucoaminidase/creatinine were evident one day postexposure in males and females exposed to 202 ppm and in males exposed to 114 ppm PIFE. Most values were within normal ranges by 4 or 14 days postexposure. No drug-related alterations in hematologic parameters were noted. Evidence of olfactory epithelial degeneration and desquamation in the nasal turbinates was noted at 4 days postexposure in male and female rats exposed to 202 ppm PIFE. Concentration-dependent renal tubular necrosis and tubular cell hyperplasia, in the corticomedullary border, were observed in males and females exposed to 114 and 202 ppm PIFE. The severity of tubular necrosis in both males and females was considered minimal to slight at the 114 ppm exposure concentration and slight to moderate at the 202 ppm exposure. Both the numbers of affected animals and severity were reduced over time. The most marked changes in serum and urine chemistry were associated with the animals described as having moderate renal necrosis. Male rats appeared more susceptible to nephropathy than female rats. There were no other PIFE-related histopathologic findings.

CONCLUSIONS

The renal histopathologic findings in this study are consistent with those reported in previous acute studies in rats after PIFE administration. Functional changes in the kidney, as evidenced by serum chemistry and urinalyses, were observed at exposure concentrations that induced morphologic alterations.

Mutagenicity of nitrobenzyl derivatives: potential bioreductive anticancer agents

Ortho-, meta- and para-nitrobenzyl bromides, alcohols, ethers and esters were synthesised and tested for their mutagenicity toward Salmonella typhimurium TA100, TA100NR (nitroreductase deficient) and TA98 in absence of S9 mix and in TA100 with S9 mix. Compounds of the ortho- and meta-series were non mutagenic with and without S9 mix. Except for the alcohol and ether, the compounds of the para-series were mutagenic in TA100 with activity sequence propionate > butyrate > benzoate > acetate > bromide and this specific activity was reduced considerably by S9 mix. The Ames Salmonella test system does not seem to be an appropriate model to evaluate mutagenicity of o-nitrobenzyls. However, further work is in progress to test all the compounds for mutagenicity in mammalian system.

Pituitary adenylate cyclase-activating peptide gene expression in corticotropin-releasing factor-containing parvicellular neurons of the rat hypothalamic paraventricular nucleus is induced by colchicine, but not by adrenalectomy, acute osmotic, ether, or restraint stress

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a newly discovered neuropeptide that is present in high amounts in hypothalamic neuroendocrine neurons and potently stimulates the accumulation of cAMP within cells of the anterior pituitary. We have employed several specific antisera recognizing different parts of the PACAP precursor to elucidate the distribution of PACAP-like immunoreactivities in the hypothalamic components of the hypothalamo-pituitary-adrenocortical axis in sections obtained from normal and colchicine-treated rats. Using immunohistochemistry with avidin-biotin-coupled peroxidase as a reporter system, high numbers of PACAP-immunoreactive perikarya were found in colchicine-pretreated rats in many of the parvicellular subdivisions of the hypothalamic paraventricular nucleus (PVN). A few cells were also found in the magnocellular subdivisions of the nucleus, and a similar small population of cells was observed in the dorsolateral aspect of the supraoptic nucleus. Using indirect immunofluorescence, the relation between CRF- and PACAP-containing neurons in the various parvicellular subnuclei of the PVN was studied, and a high degree of colocalization was demonstrated in the neurons of the medial parvicellular part of PVN. To further study the functional implications of PACAP in the hypothalamo-pituitary-adrenocortical axis, we examined the expression of PACAP messenger RNA (mRNA) in the PVN in response to five different stimulatory paradigms that previously have been shown to stimulate CRF mRNA expression in the medial parvicellular part of the PVN. The stimulatory challenges of adrenalectomy, restraint stress, ip injection of hypertonic saline, ether stress, and intracerebroventricular injection of colchicine induced significant elevations of CRF mRNA expression in the medial parvicellular part of the PVN. In contrast, the expression of PACAP mRNA, which is hardly detectable within the medial parvicellular part of the PVN, was induced only by colchicine treatment (from undetectable levels to 177 +/- 21 dpm/g; mean +/- SEM), whereas PACAP mRNA remained undetectable in this region of the PVN after exposure to any of the other stimulatory paradigms. The onset of colchicine-induced PACAP mRNA expression in the PVN was rapid (3 h), and PACAP mRNA levels remained elevated throughout the 48-h observation period. Considering the different topography and connections of the parvicellular subnuclei of the PVN, the current observations suggest that PACAP present in parvicellular neurons of the PVN may act not only as a neuroendocrine transmitter/modulator in the hypothalamo-pituitary-adrenocortical axis, but also as transmitter mediating neurotransmission conveyed from the PVN to preganglionic neurons of the autonomic system.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicological investigations in the semiconductor industry: IV. Studies on the subchronic oral toxicity and genotoxicity of vacuum pump oils contaminated by waste products from aluminum plasma etching processes

Dry etching processes in semiconductor manufacturing use ionized gases in closed reactors at pressures below 1 torr. Vacuum pump systems that service the reaction chambers are potential sources of exposure to complex mixtures of inorganic and organic compounds. These mixtures consist of unused process gases and process by-products that condense and accumulate in the vacuum pump oils. To evaluate potential hazards of dry etch vacuum equipment, a contaminated vacuum pump oil sample from a BCl3/Cl2 etching process was analyzed. The waste oil was administered by gavage for 14 or 28 days to male and female Wistar rats. Neither death nor behavioral changes occurred after subchronic treatment or during a 14-day posttreatment period. Only slight effects on body weights, clinical chemistry, and hematology data were seen in the exposed animals, although the livers of all waste oil-exposed rats of both sexes showed remarkable hypertrophic degenerations. Genotoxicological investigations were performed through the Ames assay (Salmonella assay) and the Micronucleus assay. The contaminated oil sample caused clear genotoxic effects in both test systems.

Nephrotoxicity in rats undergoing a one-hour exposure to compound A

We previously demonstrated that rats experienced renal injury when exposed for 3-12 h to 50 ppm or more of a vinyl ether called Compound A [CF2 = C(CF3)OCH2F], a compound produced by CO2 absorbents acting on sevoflurane. These durations of exposure exceed the average duration of clinical anesthesia. We now report the effect of a 1-h exposure to 0, 100, 150, 200, 400, 600, or 800 ppm of Compound A in oxygen in 145 Wistar rats. Twenty-four hours after exposure, we obtained kidney and liver specimens for microscopic examination, applying hematoxylin and eosin, and (separately) an immunochemical marker (PCNA) for cell proliferation (regeneration). Compared with results from control rats (those breathing oxygen for 1 h), renal injury (defined as necrosis of the outer strip of the outer medullary layer or "corticomedullary junction necrosis") occurred at and above 200 ppm. Exposure to 150 ppm produced cell regeneration (i.e., stimulated cell proliferation). We conclude that the threshold concentrations for nephrotoxicity (i.e., minimal toxicity) for a 1-h exposure to Compound A exceed the maximum concentrations (particularly those at low inflow rates) reported in clinical practice by a factor of 2-3. If these threshold effects in rats apply to humans, one 1-h exposure to sevoflurane probably would not alter usual measures of renal function.