Prediction of ocular irritation by corneal pachymetry.

Corneal pachymetry performed 3 days after application of a variety of test materials to the rabbit eye was found to be predictive of the eye irritation classification determined by observing the ocular response for 21 days. The test materials included NaOH, methanol, isopropanol, acetone, cyclohexanone, hexane and a shampoo. A 0.1-ml sample of the test material was placed in the conjunctival sac in the left eye of each rabbit. Both the left and the right eye of each rabbit were evaluated for irritation and corneal thickness for up to 21 days using a slit-lamp biomicroscope with a pachymeter attachment. On day 3 of observation the mean corneal thickness ratios (treated/control eye) were predictive of the duration of corneal cloudiness (correlation coefficient = 0.86). In addition, these ratios were predictive of the eye irritation classification as determined by a 21-day test (correlation coefficient = 0.98). Corneal pachymetry for determining eye irritation classification is presented as an alternative to the current 21-day test. It is more objective and requires a shorter observation period. Therefore, this method should lessen the cost of eye irritation testing and decrease the duration of discomfort that may occur among the test animals. The greater objectivity may also reduce the intra- and interlaboratory variation and the number of rabbits required for each testing.

Anticholinesterase effect and toxicity of bis(trichloromethyl) sulfone (N-1386 Biocide) in rats.

The oral LD50 for bis(trichloromethyl) sulfone (N-1386 Biocide) in male rats was 691 mg/kg. Deaths occurred 1-5 days after treatment and signs of toxicity suggestive of an anticholinesterase effect were noted. However, neither plasma cholinesterase nor brain acetylcholinesterase was inhibited 2, 4 or 24 hours after a single, oral dose of 500 mg/kg. Atropine (300 mg/kg, s.c.) or scopolamine (670 mg/kg, s.c.) pretreatments did not protect against the acute lethality of bis(trichloromethyl) sulfone although signs of toxicity were alleviated by both pretreatments. Bis(trichloromethyl) sulfone produced in vitro inhibition of rat plasma cholinesterase and brain acetylcholinesterase. The inhibition was competitive in brain. IC50's for these 2 enzymes were 8 microM in plasma and 25 microM in brain. In summary, bis(trichloromethyl) sulfone produced in vitro cholinesterase inhibition not demonstrated in vivo. Doses of anticholinergic compounds that ameliorated many toxic signs did not protect against lethality produced by bis(trichloromethyl) sulfone.

Estimation of the delayed neurotoxic potential and potency for a series of triaryl phosphates using an in vitro test with metabolic activation.

The delayed neurotoxic potential of 0,0-diphenyl-o-tolyl phosphate (MOCP), tri-o-tolyl phosphate (TOCP), 0,0-diphenyl-m-tolyl phosphate (MMCP), tri-m-tolyl phosphate (TMCP), 0,0-diphenyl-p-tolyl phosphate (MPCP) and tri-p-tolyl phosphate (TPCP) was determined using an in vitro neurotoxic esterase test with metabolic activation. None of the 6 compounds inhibited hen brain neurotoxic esterase activity in vitro when tested in the absence of metabolic activation using concentrations as high as 100 microM. Both MOCP and TOCP markedly inhibited activity in vitro after metabolism with rat liver microsomes. MOCP was twice as potent as TOCP and IC50 values were 6.2 and 12 microM, respectively. Adult hens were treated with 10 mg/kg MOCP, 10 mg/kg TOCP, 1000 mg/kp MMCP, 1000 mg/kg TMCP, and 1000 mg/kg TPCP. There was no inhibition of brain neurotoxic esterase 24 hours after MMCP, TMCP or TPCP. Inhibition by MOCP and TOCP was 86.8% and 40.7% respectively. The in vitro neurotoxicity test showed that MOCP and TOCP, 2 known neurotoxicants, had delayed neurotoxic potential and metabolism was required. The test also showed that the potency of MOCP was twice that of TOCP. This was confirmed in hens dosed with the 2 compounds since MOCP produced twice the inhibition of brain neurotoxic esterase as that produced by an equal dose of TOCP.

Skin irritation testing in rabbits complicated by dermal mucormycosis.

Two insecticide formulations were evaluated for skin irritation using albino rabbits (Stauffland-White strain). While the active ingredient alone produced only mild skin irritation, corn grit formulation produced severe skin irritation. Corn grit from three sources (A, B, and C) was similarly evaluated for skin irritation and at 24 hr, all samples produced erythema and edema of both the abraded and nonabraded test sites. Eschar was observed in 72 hr in about half of the rabbits and persisted through termination on the 7th day. Histologic examination of skin specimens revealed that all three corn grit samples produced epidermatitis. In addition, rabbits exposed to corn grit from two sources (A and B), developed moderate focal to severe diffuse suppurative necrotizing folliculitis and dermatitis. Large tubular branching nonseptate hyphae compatible with the Mucorales species were seen in hair follicle micropustules of rabbits treated with corn grit from sources A and B. Mycologic culture techniques applied to corn grit from each source revealed a potential pathogen in the genus Rhizopus isolated from samples from sources A and C but not B. The skin irritation test involved application of test material covered with gauze to both abraded and nonabraded skin. Rubber damming was placed over the gauze and secured with tape. After 24-hr exposure all bandaging and visible test material were removed. Skin irritation was evaluated immediately after removal and then periodically until termination at 7 days.

Assessment of the delayed neurotoxic potential of isopropyl triphenylphosphate using a nontraditional testing strategy.

The potential of isopropyl triphenyl phosphate (ITP) to produce delayed neurotoxicity in hens was examined using several techniques. ITP contained O,O,O-triphenyl phosphate (24%), O-o-isopropylphenyl O,O-diphenyl phosphate (25%), O,O-diisopropyl-phenyl O-phenyl phosphate (20%), O-o, p-diisopropylphenyl O,O-diphenyl phosphate (18%) and O-p-isopropylphenyl O,O-diphenyl phosphate (6%). Hens treated twice, 3 wk apart, with doses of ITP as high as 11.7 g/kg showed no clinical signs of delayed neurotoxicity and only mild signs of general toxicity. Furthermore, none showed even subtle neurohistologic changes suggestive of delayed neurotoxicity. ITP produced dose-dependent inhibition of hen plasma cholinesterase and brain neurotoxic esterase (NTE). The study was continued because NTE inhibition has been shown to be a reliable predictor of organophosphates that produce delayed neurotoxicity. ITP was administered prior to tri-o-tolyl phosphate (TOCP) challenge in order to determine if it altered development of TOCP delayed neurotoxicity. ITP neither enhanced nor reduced the onset or severity of neurotoxicity produced by TOCP. The time-course for brain and spinal cord NTE inhibition by ITP and TOCP were compared and found to be different. The maximum brain NTE inhibition produced by ITP (doses up to 11.7 g/kg) was never complete (always less than 90%), and spinal cord NTE inhibition was significantly less than that produced in the brain. In contrast, brain and spinal cord inhibition produced by 500 mg TOCP/kg were equal and greater than 90%. This testing regimen showed that ITP produced an effect on NTE at the biochemical level without producing clinical or neurohistologic abnormalities in treated hens. Furthermore, this biochemical effect was qualitatively different than that produced by the delayed neurotoxicant TOCP.

Alteration of brain chromatin and nuclear synthetic activity in morphine-tolerant rats.

3H-UTP incorporation by endogenous RNA-polymerase of intact, isolated rat brain nuclei was enhanced by chronic morphine treatment. Analgesic tolerance using the hot-plate assay was also evident. Fractionation proflies for brain chromatin on hydroxylapatite from morphine and vehicle-treated rats was different. These results suggest that morphine-tolerance in the rat may be accompanied by enhanced nuclear synthesis of a new species of RNA.