Absence of Developmental Effects in CF-1 Mice Exposed to Aspartame in Utero

Aspartame (L-aspartyl-L-phenylalanine methyl ester) is a widelyused high potency dipeptide sweetener. Developmental toxicologystudies have been performed in several species documenting noeffects of high doses of aspartame. Recently, a study by Mahalikand Gautieri ((1984) Res Commun. Psychol Psychiatry Behav. 9,385–403) reported a delay in the achievement age for thevisual placing response in mice pups after maternal administrationof high dosages of aspartame during late gestation. In the presentstudy developmental parameters were determined in offspringof CF-1 mice after maternal administration of aspartame at 500,1000, 2000, and 4000 mg/kg body wt by oral gavage. Aspartamewas administered on Days 15 through 18 of gestation. Maternalbody weight, food consumption, gestation length, reproductiveindices, and litter size were not affected by aspartame treatment.In the pups, body weights, negative geotaxis, and surface andmidair righting reflexes were not altered by treatment. Therewas no delay in the development of the visual placing responseregardless of the method employed for assessment (grid or rope)or the manner by which the data were analyzed. There were alsono changes in time of eye opening, reflex pupil closure, andophthalmoscopic examination in the offspring. Thus, neitherphysical nor functional development was altered in mice afterin utero exposure to extremely large dosages of aspartame. Morespecifically, in utero exposure to aspartame did not affectthe development of the visual system in mice.     

Dose-Dependent Carcinogenicity and Frequent Ki-ras Proto-oncogene Activation by Dietary N-Nitrosodiethylamine in Rainbow Trout

While the experimental data upon which current concepts in mechanisticallybased risk assessment and molecular epidemiology are groundedderive almost entirely from rodent models, fish models haveseveral attributes (e.g., low background incidence, extremelylow cost tumor studies, nonmammalian comparative status forextrapolation of mechanisms to humans) that make them valuableadjuncts for addressing these concepts. This report providesan initial characterization of the dose dependency of dietaryN-nitrosodiethylamine (DEN) hepatocarcinogenicity in Shastastrain rainbow trout (Oncorhynchus mykiss) and the potentialof DEN to elicit ras proto-oncogene activation in this species.Carcinogen was administered in the diet at five concentrationsfor 12 months. Necropsies were per formed at 9, 12, and 18 months,the latter on fish maintained on control diet for 6 months aftercessation of DEN exposure. The incidence of hepatic neoplasmsat the lower dietary concentrations (70 ppm) did not consistentlyexceed that for control groups, which were higher in this particularstudy (2%) than expected (historically 0.1%). For the higherDEN concentrations, a linear relationship between the hepatictumor incidence (expressed as log odds, log [p/(1-p)1, wherep = proportion of fish bearing tumors), and the logarithm oftotal cumulative dose was observed, with response being independentof the length of time (9 or 12 months) during which the dosewas accumulated. The dose-response curve for fish maintainedan additional 6 months postexposure was shifted toward higherincidence but was parallel to the curve for fish killed at cessationof exposure. The model predicts that doubling the dose willproduce some what more than a doubling of the odds (pl(100 -p) for tumor incidence and that the odds for lesions 6 monthspostexposure will be approximately double those at cessationof exposure. Comparison of these results with previous studiesusing rats suggests an overall similarity in dose-response curves,with trout being somewhat less sensitive than rats to DEN hepatocarcinogenesis. To examine the molecular basis for DEN carcinogenesis in this species, seven liver tumors induced separatelyby short-term DEN treatment were probed by 3'-mismatch primerpolymerase chain reaction analysis for evidence of Ki-ras proto-oncogeneactivating point mutations. A very high proportion (6/7) oftumors was found to carry codon 12 GGA - AGA mutations, whereasno codon 61 mutants were detected in this sample. These initialresults differ from those reported using hepatic tumors fromDEN-treated mice, which exhibit frequent Ha-ras codon 61 mutations[Richardson et al., Carcinogenesis 13, 1277–1279 (1992)]and rats, which appear not to carry DEN-activated ras alleles[Bauer-Hoffman et al., Carcinogenesis 11, 1875–1877 (1990)].Thus the available oncogene data for the common carcinogen DENdo not suggest a simple, consistent oncogenic pathway or mutationalspectrum useful in the molecular epidemiology of human cancers.     

CHOLECYSTOKININ (PANCREOZYMIN)

The acetyl-derivative of the biologically active C-terminal 7-peptide portion of cholecystokinin (CCK), N-acetyl-O-sulfate-L-tyrosyl-L-methionyl-glycyl-L-tryptophyl-L-methionyl-L-aspanyl-L-phenylalanine amide was prepared by the condensation of 2-peptide segments with 1-isobutyloxycarbonyl-2-isobutyloxy-1,2-dihydroquinoline as coupling reagent. The N-terminal residue, tyrosine, was incorporated by the active ester method. The same 7-peptide was prepared also by stepwise chain-lengthening, starting with the C-terminal residue. The 9-fluorenylmethyloxycarbonyl group was applied for the protection of α-amino functions. In the release of amylase from acinar cells of the pancreas of guinea pigs, the acetyl-7-peptide amide was about 3 times more potent than CCK 27–33 and equal in potency to CCK 26–33. The new derivative strongly stimulated the contraction of the in situ guinea pig gall bladder.     

Five-Month Oral (Diet) Toxicity/lnfectivity Study of Bacillus thuringiensis Insecticides in Sheep

Five-Month Oral (Diet) Toxicity/Infectivity Study of Bacillusthuringiensis Insecticides in Sheep. HADLEY, W. M., BURCHIEL,S. W., MCDOWELL, T. D., THILSTED, J. P., HIBBS, C. M., WHORTON,J. A., DAY, P. W., FRIEDMAN, M. B., and STOLL, R. E. (1987).Fundam. Appl. Toxicol. 8, 236–242. Bacillus thuringiensisinsecticides (Bt) [Dipel (test substance D or Thuri-cide-HP(test substance T)] were administered in the diet for 5 monthsto castrated mixed ram-bouillet/merino sheep (24–34 kgat the beginning of the study) at a dose of 500 mg/kg/day (approximately10¹² spores per day). No treatment-related effect was seen onweight gain or clinical chemistry parameters nor were significantgross clinical changes observed. Several blood and tissue samplestaken just prior to the time the animals were killed or at necropsywere found to be positive for Bt when cultured. Detailed grossand microscopic pathologic examination of the sheep revealedseveral incidental lesions. However, the only lesion that mayhave been associated with the treatment was lymphocytic hyperplasiain Peyer's patches seen in the cecum of three sheep and it wasnot considered to be clinically significant.     

Stroke Volume and the Three Phase Cardiac Output Rate Relationship with Ventricular Pacing

Knowledge of how stroke volume (SV), and hence cardiac output (CO), changes with ventricular pacing rate (R) constitutes a key aspect of sensor driven, variable rate pacemakers. It has been established that the relationship between CO and pacing rate exhibits three phases for rest and constant exercise. At low rates (phase 1), CO increases with increasing R; with additional rate increase (phase 2), CO either remains constant or increases slightly; and above some critical rate, CO decreases (phase 3). However, the nature of the relationship between SV and pacing rate has not been as clearly described. Therefore, the objectives of this study were (1) to describe and document the relationship between SV and R, and (2) to demonstrate the consequence of this relationship in terms of the three phase CO versus R relationship. In six anesthetized dogs, right ventricular SV was determined from pulmonary artery blood flow measured using an electromagnetic flow meter, and the right ventricle was paced over a range of rates. In general, SV decreased with increasing R, although the exact nature of the relationship varied from animal to animal. The results demonstrate that it is the manner in which SV decreases with increasing R that determines the three phase relationship between CO and R. The relationships described in this study have important implications for choosing pacing rates for patients receiving sensor driven, variable rate pacemakers.     

The Developmental Toxicity of Orally Administered Oxytetracycline in Rats and Mice

The Developmental Toxicity of Orally Administered Oxytetracyclinein Rats and Mice. MORRISSEY, R.E., TYL, R.W., PRICE, C.J., LEDOUX,T.A., REEL, J.R., PASCHKE, L.L., MARR, M.C, AND KJMMEL, C.A.(1986). Fundam. Appl. Toxicol. 7, 434-443. Timed-pregnant CDrats and CD-1 mice were dosed by gavage with oxytetracyclinehydrochloride (OXT) in corn oil on gestational days (gd) 6-15(0, 1200, 1350, or 1500 mg/kg/day for rats; 0, 1325, 1670, or2100 mg/kg/day for mice). Deaths among treated females occurredin a dose-related manner in all OXT dose groups (2-7%, mice;5-24%, rats), but no maternal deaths occurred in the vehiclecontrol groups. Significant dose-related decreases in maternalweight gain during treatment, as well as for corrected gestationalweight gain (i.e., maternal gestational weight gain minus graviduterine weight), were observed at all doses in rats but notin mice. Gravid uterine weight was reduced in a dose-relatedmanner only in mice, with the high-dose group significantlyreduced compared to the control group. At termination (gd 20,rats; gd 17, mice), the status of uterine implantation siteswas recorded and live fetuses were weighed. Fetuses were examinedfor external, visceral, and skeletal abnormalities. There wereno significant effects of OXT in either species on the incidenceof postimplantation loss (resorptions plus dead fetuses) ormalformations. In both species, there was a significant trendtoward reduced fetal body weight, and each group of rats receivingOXT was significantly reduced compared to the control group.Administration of OXT during organogenesis at doses exceedingthe therapeutic range for humans produced maternal and fetaltoxicity, but did not produce any treatment-related increasein malformations.     

Immunotoxicity Testing: An Economical Multiple-Assay Approach

Immunotoxicity Testing: An Economical Multiple-Assay Approach.EXON, J.H., KOLLER, L.D., TALCOTT, P.A., O'REILLY, C.A., ANDHENNINGSEN, G.M. (1986). Fundam Appl. Toxicol. 7, 387-397. Amodel for assessing immunotoxicologic effects of chemicals anddrugs was developed in the Sprague-Dawley rat whereby multipleconcomitant immunoassays were performed in a single animal.The multiple parameters of immunity assessed in each rat includedT cell-dependent IgG antibody production, delayed hypersensitivity,natural killer cell cytotox-icity, and production of three potentimmune regulating immunocytokines: macrophage-de-rived interleukin1 and prostaglandin E2, and lymphocyte-derived interleukin 2.Splenocyte and resident peritoneal macrophage numbers were alsoquantitated and spleen and thymus weights recorded. The sensitivityof this animal model was tested by treating rats with the immune-potentiatingdrugs, NPT 15392 (erythro-9-[2-hydroxy,3-nonyl]hypoxanthine)and avridine (N, N-dioctadecyl-N', N'-bis-[2-hydroxyethyl]propanediamine,or the immune-suppressive drugs, cyclophosphamide (N, N-bis[2-chloroethyl]tetrahydro-2H-1,3,2-oxazaphosphorin-2-amine-2-oxide)and dexamethasone. Rats treated with NPT 15392 or avridine generallyhad enhanced immune responses, while those treated with cyclophosphamideor dexamethasone had decreased immune responses. Differentialresponsiveness of various immunocyte populations within individualrats to different drugs, or to doses of the same drug, indicatesthe efficacy of measuring multiple responses within the sameanimal. The multiassay-single animal approach represents aneconomical, versatile, sensitive, and relatively comprehensiveparadigm for assessing immunotoxicologic/pharmacologic propertiesof chemicals and drugs. The approach is extremely economicalsince multiple immune responses are evaluated in each animal.The approach is versatile because it is amenable to incorporationof a variety of in vitro and in vivo assays and could be appliedto almost any species. The model is relatively comprehensivebecause major types of immune responses/immunocyte populationsand immunoregulatory pathways are tested. Finally, the modelis sensitive for detecting immunosuppression as well as immunoenhancement,as validated by the use of known immune response modifiers inthis Study.     

Termination Of Sustained Tachycardia By External Noninvasive Pacing

Invasive cardiac pacing has proved useful in the induction and termination of reentrant sustained tachycardias. In one of our two cases, programmed ventricular extra-stimulation was used to induce sustained ventricular tachycardia from the endocardial surface of the right ventricle. Induced ventricular tachycardia was terminated by burst ventricular pacing with an external cardiac pacemaker. In our second patient, external pacing was effective at inducing and terminating sustained supraventricular tachycardia. These patients illustrate that the principles of terminating sustained reentrant tachycardia with invasive pacing may also apply to noninvasive external pacing. The usefulness of this approach in treating reentrant tachycardias needs further evaluation.