Technetium-99m benzimidazolyl iminodiacetic acid hepatobiliary radiopharmaceuticals: structure biodistribution studies

The biodistribution of fifteen structural variants of the hepatobiliary radiopharmaceutical, technetium-99m benzimidazolyl iminodiacetic acid (BIMIDA) were determined 1 h after i.v. injection into rats. The best compounds with respect to hepatobiliary excretion were those with halogen substituents in the benzene ring of the BIMIDA ligand. The cholescintigraphic properties of the BIMIDA compounds compared favourably with those of technetium-99m acetanilido iminodiacetic acid (HIDA) radiopharmaceuticals.

Characterization of human T lymphocytes that express the C3b receptor

The presence of the C3b receptor (C3bR) on human peripheral blood T lymphocytes was recognized by the capacity of rabbit F(ab')2 anti-C3bR and tetramethylrhodamine isothiocyanate (TRITC)-conjugated goat F(ab')2 anti-rabbit F(ab')2 to stain 14.5 +/- 3.7% (mean +/- SEM; n = 5) of lymphocytes forming rosettes with sheep erythrocytes (E). The F(ab')2 anti-C3bR also blocked the capacity of peripheral blood lymphocytes stained with OKT11 to form rosettes with bovine E bearing C3b and immunoprecipitated a single membrane protein having a m.w. of approximately 250,000 from detergent lysates of 125I-labeled, purified T cells. Measurement by fluorescent flow cytometry of the quantitative expression of the C3bR indicated that T cells had slightly more antigenic sites/cell than did E and approximately 10-fold fewer sites than were present on B cells. The surface constituents of the peripheral blood T cells expressing the C3bR were assessed in an assay that employed simultaneously three markers: rosette formation with sheep E, TRITC staining with anti-C3bR and fluorescein isothiocyanate (FITC)-staining with a panel of monoclonal antibodies or with aggregated IgG. Among lymphocytes forming rosettes with sheep E and expressing the C3bR, 99.6 +/- 0.4%, 65.0 +/- 5.8%, 17.2 +/- 6.2%, and 15.3 +/- 5.0% of the cells expressed antigens detected by OKT3, OKT4, OKT8, and OKM1 monoclonal antibodies, respectively. Ninety-seven per cent of the C3bR-bearing T cells were also capable of specifically binding aggregated IgG, indicating the presence of Fc receptors for IgG (Fc gamma R) on these cells. The T cells expressing the C3bR had large nuclei, thin rims of basophilic cytoplasm and no azurophilic granules. Thus, the C3bR is present on some T cells, all of which have a typical lymphocyte morphology, the T3 antigen and the Fc gamma R.

Characterization of human T lymphocytes that express the C3b receptor

The presence of the C3b receptor (C3bR) on human peripheral blood T lymphocytes was recognized by the capacity of rabbit F(ab')2 anti-C3bR and tetramethylrhodamine isothiocyanate (TRITC)-conjugated goat F(ab')2 anti-rabbit F(ab')2 to stain 14.5 +/- 3.7% (mean +/- SEM; n = 5) of lymphocytes forming rosettes with sheep erythrocytes (E). The F(ab')2 anti-C3bR also blocked the capacity of peripheral blood lymphocytes stained with OKT11 to form rosettes with bovine E bearing C3b and immunoprecipitated a single membrane protein having a m.w. of approximately 250,000 from detergent lysates of 125I-labeled, purified T cells. Measurement by fluorescent flow cytometry of the quantitative expression of the C3bR indicated that T cells had slightly more antigenic sites/cell than did E and approximately 10-fold fewer sites than were present on B cells. The surface constituents of the peripheral blood T cells expressing the C3bR were assessed in an assay that employed simultaneously three markers: rosette formation with sheep E, TRITC staining with anti-C3bR and fluorescein isothiocyanate (FITC)-staining with a panel of monoclonal antibodies or with aggregated IgG. Among lymphocytes forming rosettes with sheep E and expressing the C3bR, 99.6 +/- 0.4%, 65.0 +/- 5.8%, 17.2 +/- 6.2%, and 15.3 +/- 5.0% of the cells expressed antigens detected by OKT3, OKT4, OKT8, and OKM1 monoclonal antibodies, respectively. Ninety-seven per cent of the C3bR-bearing T cells were also capable of specifically binding aggregated IgG, indicating the presence of Fc receptors for IgG (Fc gamma R) on these cells. The T cells expressing the C3bR had large nuclei, thin rims of basophilic cytoplasm and no azurophilic granules. Thus, the C3bR is present on some T cells, all of which have a typical lymphocyte morphology, the T3 antigen and the Fc gamma R.

Genetic regulation of a structural polymorphism of human C3b receptor

Two forms of the human C3b receptor (C3bR), which have relative molecular weights (Mr) of 250,000 and 260,000 and are designated F and S, respectively, have been identified in specific immunoprecipitates from erythrocytes and leukocytes by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Both forms of the receptor were visualized on gels by autoradiography of 125I-labeled antigen and by silver nitrate staining. Individual donors expressed one of three possible patterns of C3bR, either the F or S form alone or both, and these patterns represented stable phenotypic characteristics of their erythrocytes and polymorphonuclear and mononuclear leukocytes. Removal of N-linked oligosaccharides by endoglycosidase-F treatment decreased the Mr of both forms but did not abolish the difference in their electrophoretic mobilities. That both forms of the receptor were functional was indicated by the capacity of all antigenic C3bR sites on erythrocytes from individuals having any of the three phenotypes to bind dimeric C3b with affinities ranging from 3 to 5 X 10(7) M-1. Analyses of the occurrence of the F and S forms of C3bR in 76 individuals from 15 families revealed that this polymorphism was regulated by two alleles transmitted in an autosomal codominant manner. Of 111 normal unrelated individuals, 64.9% were homozygous for the F form (FF), 1.8% were homozygous for the S form (SS), and 33.3% were heterozygotes (FS). This distribution did not differ from that calculated by the Hardy-Weinberg equilibrium based on two codominant alleles that regulate the expression of the F and S forms and that have frequencies of 81.5 and 18.5%, respectively. The locus regulating structural polymorphism of C3bR is designated C3BRM (M for mobility or Mr), and is distinct from the recently described locus regulating the quantitative expression of C3bR on erythrocytes.

Iminodiacetic acid derivatives of benzimidazole. Synthesis of N-(Benzimidazol-2-ylmethyl)iminodiacetic acids

Ten new N-(2-benzimidazolylmethyl)iminodiacetic acids (BIMIDA)* have been synthesized from the corresponding o-phenylenediamines via intermediate 2-chloromethyl and 2-aminomethyl benzimid- azoles as ligands for 99mTc. Anomalies associated with the synthesis of the iodo-substituted compound are described.

Acetazolamide teratology and its association with carbonic anhydrase inhibition in the mouse

Acetazolamide, an inhibitor of the enzyme carbonic anhydrase (E.C. 4.2.1.1.), causes a unique congenital anomaly characterized by postaxial reduction of the distal portion of the right forelimb. To gain an understanding of the mechanism of teratogenesis, the activity of carbonic anhydrase in sensitive and resistant mouse strains, and its inhibition by acetazolamide, were examined. Differences in teratologic sensitivity were found not to be attributable to differences in maternal or embryonic drug levels. Enzyme inhibition at acetazolamide concentrations ranging between 10(-11) and 10(-5) M did not differ between the mouse strains when adult erythrocytes or day 12 embryos were assayed. However, in day 10 embryos, the period of maximum teratologic susceptibility, a small strain difference was found which suggested that the form of carbonic anhydrase in the susceptible CBA/J strain at this time is somewhat more sensitive to inhibition by acetazolamide than the form found in the resistant SWV strain. The results suggest further that more than one isozyme of carbonic anhydrase may be present in all three samples.

A selection of candidate compounds for in vitro teratogenesis test validation

The Consensus Workshop on In Vitro Teratogenesis Testing recommended that test validation be facilitated by a listing of agents with defined teratogenicity; subsequently, a panel was convened to review and select such agents. This communication established a list of 47 compounds or conditions which demonstrate a wide range of teratogenicity in vivo. The agents were chosen primarily on the strength of the literature base denoting their in vivo effects. The tables note a number of general biological and toxicological characteristics for each agent, and the details of representative in vivo teratology studies are summarized and referenced. This list is intended to serve as a base for in vitro teratogenesis test validation and should prove useful in developing and identifying those systems which will contribute to a more effective testing program.

Mode of inheritance of decreased C3b receptors on erythrocytes of patients with systemic lupus erythematosus

The erythrocytes of patients with systemic lupus erythematosus have been shown to have a decreased number of receptors for the major cleavage fragment of the third component of complement (C3b). We studied the basis for this decreased number of C3b receptors by measuring the uptake of anti-C3b-receptor antibody on cells from 113 normal subjects, 38 patients with systemic lupus erythematosus, 14 of their spouses, and 47 of their relatives. The normal subjects had 5014 +/- (mean +/- S.E.M.) receptor sites per cell, but the patients and their relatives had significantly fewer sites--2809 +/- 241 and 3167 +/- 196, respectively (P less than 0.0005). The number of sites in the patients' spouses did not differ from normal (P greater than 0.3). Three phenotypes, indicated by the numbers of receptors, occurred in the normal population; a high phenotype (HH, with 5500 to 8500 sites per cell), an intermediate phenotype (HL, with 3000 to 5499), and a low phenotype (LL, less than 3000). These three phenotypes were present in 34, 54, and 12 percent, respectively, of the normal subjects; in contrast, 5, 42, and 53 per cent of patients had these respective phenotypes. Pedigree analyses indicated that these phenotypes were inherited in an autosomal codominant manner. We conclude that the decreased number of C3b receptors in lupus is inherited, not acquired.

Potentiative interactions between caffeine and various teratogenic agents

Acetazolamide and inhibitors of DNA synthesis (hydroxyurea, 5-fluoro-2'-deoxyuridine), RNA synthesis (actinomycin D), and protein synthesis (cycloheximide, emetine) were each administered to pregnant rats together with caffeine at doses where each agent alone caused minimal embryotoxicity. Caffeine co-administered with any of the other agents induced a powerful potentiative response. It is not clear from the present experiments whether much lower caffeine dosage, as normally encountered in humans, would potentiate embryotoxicity due to other agents.

Are female sex hormones teratogenic?

An analysis of available epidemiologic data leads the present reviewers to conclude that the use of exogenous hormones during human pregnancy has not been proved to cause developmental abnormality in nongenital organs and tissues. This conclusion is further supported by the animal laboratory data. The preponderance of evidence at this writing indicates a lack of causal association between hormonal use during pregnancy and nongenital malformation of the offspring. The quality of the epidemiologic data does not, at this time, permit a definitive conclusion that sex hormones during pregnancy may not, under as yet to be defined conditions, have some adverse effect on human prenatal development. If there are increased risks of nongenital malformations associated with the administration of certain sex steroids, the risks are very small, may not be causal, and are substantially below the spontaneous risk of malformations. In spite of the present degree of uncertainty, the clinical, epidemiologic, and laboratory data do permit the formulation of a rational approach to handling problems related to sex steroid usage and exposure in pregnant women.

Indomethacin--placental transfer, cytotoxicity, and teratology in the rat

Aspirin is a well-known teratogen in laboratory animals and is an inhibitor of prostaglandin synthesis. To further investigate the inhibition of prostaglandin synthesis as a mechanism of teratogenesis, we examined the teratologic potential, cytotoxic potential, and placental transfer of indomethacin in the rat. Indomethacin was not teratologic, not cytotoxic to cells in the embryonic hindlimb bud, and did not cross the placenta in physiologically significant amounts on days 11 to 12 of gestation. Near parturition, however, indomethacin crossed the placenta in pharmacologically significant amounts. The pharmacokinetics of placental drug transfer are discussed.

Comparative studies on acetazolamide teratogenesis in pregnant rats, rabbits, and rhesus monkeys

Acetazolamide produces a characteristic forelimb reduction deformity when administered to pregnant rodents. Past studies indicated that non-rodent species (rabbit and monkey) are resistant to this effect. The present studies confirmed this fact and demonstrated that transport of acetazolamide into the rabbit embryo was similar to that in sensitive rat embryos. In monkeys, however, the concentrations of acetazolamide within maternal plasma and embryo were much lower than in rats. Carbonic anhydrase activity was also measured since inhibition of this enzyme is the primary pharmacologic effect of acetazolamide. Again the rabbit embryo had carbonic anhydrase specific activity levels similar to that of the rat. Monkey embryos, on the other hand, contained negligible levels of enzyme activity during the presumed sensitive period of development. Thus the resistance of monkey embryos to acetazolamide teratogenesis may be due to low carbonic anhydrase activity and/or the small amount of drug reaching the embryo. No basis for the resistance of rabbit embryos to acetazolamide teratogenesis was uncovered.

Aspirin-induced teratogenesis: a unique pattern of cell death and subsequent polydactyly in the rat

Offspring of pregnant rats treated with a high dose of aspirin on day 11 of gestation frequently had predominantly right-sided polydactyly of the hindlimbs at term. Aspirin-treated embryos removed on day 12 exhibited a unique pattern of preaxial mesodermal cell death in the hindlimb buds. In addition, these embryos had a delay of the normal episode of cells death in the preaxial apical ectodermal ridge and an absence of cell death in a zone of physiological necrosis in the preaxial mesoderm thought to be instrumental in controlling preaxial digit formation. The role of cell death in the pathogenesis of polydactyly is discussed.

Problems encountered in the early diagnosis and management of congenital dislocation of the hip

This paper reports the results of screening 53033 infants for congenital dislocation of the hip between 1970 and 1979, and compares them with the results of a similar screening programme between 1960 to 1969. The number of dislocations missed at neonatal examination is unaltered at 0.11 per cent of live births. Operative treatment was needed in a further 0.07 per cent of the recent series even though the dislocations had been diagnosed within 24 hours of birth. The reasons for the failure of neonatal screening are discussed, and suggestions are made which will improve the situation.

A metabolite of a structural analog of thalidomide lacks teratogenic effect in pregnant rhesus monkeys

A metabolite of CG 3033, a structural analog of thalidomide, was examined for teratogenic potential in rhesus monkeys. The metabolite EM 240 is produced in man by hydrolysis of the parent compound but the pathway is absent in nonhuman primates. Fifteen mg/kg administered orally throughout organogenesis to pregnant rhesus monkeys produced no evidence of embryotoxicity, including malformation.

Effect of 5-fluoro-2'-deoxyuridine on deoxyribonucleotide pools in vivo

5-Fluoro-2'-deoxyuridine (FdUrd) lowered the dTTP levels in rapidly frozen 12-day W rat embryos and in a human neuroblastoma grown in nude N:NIH(S) mice to about 20% of control values. This effect was associated with greatly increased dCTP levels and reduction of dGTP levels essentially to zero. Elimination of the dGTP pool correlated temporally with the cytotoxicity of FdUrd. Extremely rapid fixation of tissue was required to avoid artifactually high deoxyribonucleoside triphosphate values.

Chronic mucocutaneous candidiasis. Immunologic studies of three generations of a single family

A family consisting of eight members in three generations (age 10 months to 53 years) affected with chronic mucocutaneous candidiasis was studied along with three unaffected relatives. Dermatophytosis, loss of teeth and recurrent viral infections were present in some members. Results of tests for endocrinologic, muscle or liver disease, thymoma, iron deficiency, antitissue antibodies and malabsorption were normal in all patients. Antibody function and levels, B cell counts, serum complement, leukocyte enzymes, chemotaxis, phagocytosis and adherence were normal in all members. Plasma inhibitors to lymphocyte transformation and leukocyte inhibitory factor were not found. No unique HLA haplotype or antigen segregated in this family. Evaluation of cell-mediated immunity revealed total cutaneous anergy in three of eight whereas four of the other five had negative lymphocyte transformation and skin tests to Candida but responded normally to other antigens. Leukocyte inhibitory factor was not produced to Candida antigen in all four patients tested. T cell counts were within normal limits in all. Extensive evaluation of all limbs of the immune system in this family revealed a defect in cell-mediated immunity to Candida that appeared to be inherited as a dominant characteristic.

The evolution of teratological testing

The beginnings of mammalian experimental teratology in this century are briefly reviewed and it is noted that prior to 1960 a degree of sophistication in concept and technology had already been achieved. Thus, contrary to claims that teratology had its beginning with the thalidomide catastrophe, a modest but expanding activity and body of knowledge already existed before this unfortunate event. This activity and this knowledge, however, were largely confined to academic and research institute laboratories and made little impact on the agencies in medicine, government and industry which oversaw public health and safety and set policies intended to preserve them. No individual, group, or agency can rightly be blamed for not having sooner brought together the concepts and methodology needed for meaningful animal testing and the regulatory insignt and experience needed intelligently to apply test data to human safety evaluation and experience needed intelligently to apply test data to human safety evaluation. To accomplish this liaison seems to have required the largest toxicological catastrophe yet recorded in human history. The major events leading to formulation of the first standardized guidelines are reviewed, but it is emphasized that even today the best animal testing can only provide a limited statement of probability regarding human risk vis-à-vis safety.

Ethanol and heat-treated plasma fractionation methods in South Africa

Modifications of the Cohn techniques are the methods of choice for the preparation fo dilute albumin (PPS) and gamma-globulin solutions on an industrial scale. For the manufacture of refined albumin solutions, however, considerable labour and material is saved if crude, ethanol-precipitated fractions are heated in the presence of stabilisers in order to purify the albumin. The technique is simple and cheap, and yields a safe product of high quality. Bacterially contaminated and highly haemoglobinized plasma can be successfully heat-treated.

Review of in vitro systems with potential for use in teratogenicity screening

In this review an in vitro system is considered to be any developing tissue, organ, or organism other than mammalian embryo in situ. Before the various test systems that have been used or proposed are discussed, attention is given to the questions of whether all chemicals in the environment are in need of biological testing and what criteria should be used in making this judgment. Consideration is also given to selection of the appropriate level of rigorousness to be used in tests of different categories of chemicals. To aid in this, the characteristics of an optimal test are assembled and used as a standard for estimating the potential usefulness of the various in vitro systems. The systems discussed include bacteria and other unicellular organisms, somatic cells in culture, tissue culture, organ culture, intact invertebrate embryos (e.g., drosophila, sea urchins, sand dollars), intact lower vertebrate embryos (e.g., frogs, other amphibians, fish), cultured mammalian embryos, and incubating chick embryos. None of these are regarded as sufficiently validated in terms of comparisons with known teratogenic responses in pregnant mammals to warrant adoption as a reliable test at this time. Intact embryos of drosophila, sea urchins, amphibians, and fish are regarded as promising, but much research is needed to ascertain their predictive validity for mammals. The incubating chick embryo, however, possesses more of the essential features of the optimal system than any of the others. A tentative proposal using the chick is outlined, but it will require considerable further comparison with currently used procedures in pregnant mammals before its reliability can be fully evaluated.

Delayed appearance of ectodermal cell death as a mechanism of polydactyly induction

The temporal program of cell death in the apical ectodermal ridge and mesoderm of rat embryo hindlimbs was documented using supravital staining with Nile blue sulfate. Dye uptake indicative of cell death began postaxially at about 290 h of development and was followed in a few hours by preaxial staining, which became more extensive and intense up to 313 h.

Two agents which cause preaxial polydactyly, cytosine arabinoside and 5-fluorodeoxyuridine, postponed the onset of preaxial ectodermal cell death while at the same time having the expected cytotoxic effect on limb-bud mesoderm. In addition, a zone of deep preaxial mesodermal necrosis, thought to control the size of digit 1 in normal embryos, was usually absent in cytosine-arabinoside-treated embryos.

The results suggest that the prolonged survival of ectodermal cells effected an increased inductive activity on the underlying mesoderm, leading to the formation of excess digital tissue. The data further suggest that the rate at which mesodermal cells were killed affected the subsequent delay of ectodermal cell death.

Non-confirmation of thalidomide induced teratogenesis in rats and mice

It has been reported that thalidomide, dissolved in a 1:3 mixture of Tween 20 and physiological saline and administered intraperitoneally to pregnant mice and rats induces a variety of malformations, including limb deformaties, characteristic of the primate syndrome. The studies reported herein attempted to confirm these findings without success although the rodent strains used were not the same. A low level of non-specific malformations was observed in the fetuses of both species at dose levels reported to cause a 47 percent and 92 percent rate of malformation in mice and rats respectively. One possible source of difference was Tween 20 which was toxic to the point of lethality in these studies at dose levels reported to be non-toxic in the earlier studies.

The effects of thalidomide and two analogues on the regenerating forelimb of the newt

Oral administration (3 mg/day) of thalidomide during the dedifferentiation and early limb-bud stages of newt forelimb regeneration produced a variety of specific limb deformities. Proximal and preaxial skeletal elements were the most severely malformed, e.g. preaxial hemimelia, severe proximal deformities, and preaxial polydactyly. Likewise, oral, daily doses (3 mg) of the teratogenic analogue, EM12, on days 7 and 8 following bilateral amputation caused the same incidence and type of forelimb abnormalities as did thalidomide. Conversely, the non-teratogenic analogue, EM87, when orally administered (3 mg/day) on days 7 and 8 post-amputation resulted in a low rate of limb deformities, similar in type to those seen in control regenerates. The type of limb deformities observed in the regenerating newt forelimb following thalidomide treatment nearly mimic those seen in the human and monkey syndromes. Therefore, the newt represents a possible model for investigating some of the problems associated with thalidomide teratogenesis.

The effects of thalidomide and two analogues on the regenerating forelimb of the newt

Oral administration (3 mg/day) of thalidomide during the dedifferentiation and early limb-bud stages of newt forelimb regeneration produced a variety of specific limb deformities. Proximal and preaxial skeletal elements were the most severely malformed, e.g., preaxial hemimelia, severe proximal deformities, and preaxial polydactyly.

Likewise, oral, daily doses (3 mg) of the teratogenic analogue, EM12, on days 7 and 8 following bilateral amputation caused the same incidence and type of forelimb abnormalities as did thalidomide. Conversely, the non-teratogenic analogue, EM87, when orally administered (3 mg/day) on days 7 and 8 post-amputation resulted in a low rate of limb deformities, similar in type to those seen in control regenerates.

The type of limb deformities observed in the regenerating newt forelimb following thalidomide treatment nearly mimic those seen in the human and monkey syndromes. Therefore, the newt represents a possible model for investigating some of the problems associated with thalidomide teratogenesis.

Teratogenic effects of environmental chemicals

Despite the widespread distribution of a great many chemical substances in the environment, very few have been implicated in human teratogenicity, and most of these are drugs used at relatively high biological effect levels. Although several other types of environmental chemicals such as pesticides, solvents, and metals can be shown under laboratory conditions to have some teratogenic potential, there is little evidence that these, at present ambient concentrations and conditions of exposure, represent significant hazards to human intrauterine development. An exception to the latter generalization is methylmercury which, because of peculiarities in distribution, can reach high concentration in the human diet.

Embryotoxicity of the folate antagonist methotrexate in rats and rabbits

The prenatal effects of methotrexate (MTX) in rats and rabbits were assessed. It was found highly embryotoxic in postimplantation rat embryos; 0.3 mg/kg ip or less caused nearly total embryolethality with slight teratogenicity. Rabbit embryos were far more resistant to small doses of MTX than rats, but 19.2 mg/kg iv, when given during days 10 to 15 of gestation, produced little death and a constant spectrum of malformation in a high percentage of offspring. Cleft palate, skull defects, and severe fore- and hindlimb dysplasias, occurred with a high degree of regularity and were strongly dose and developmental-stage specific.

Reduced interlitter variability in rats resulting from a restricted mating period, and reassessment of the ""litter effect''

Rats were mated for two or 15 hours and variability of day-12-embryos in weight, protein content, and [3H]thymidine incorporation was compared in the long mating period (LMP) and short mating period (SMP) groups by a 2-level nested analysis of variance. Variability in day-20 fetal weight was similarly compared. In both groups day-12 embryonic weight was relatively more variable than day-20 fetal weight, and variability was less in SMP than LMP animals for each comparison made, although statistical significance was attained only for thymidine incorporation. ""Litter effects'' were noted but not of the magnitude reported by other investigators. It was concluded that inappropriate statistical methods have encouraged the belief that among-litter variability usually exceeds within-litter fetal weight variability. The teratological implications of reduced development variability and the ""litter effect'' are discussed.

Inhibition of ATP synthesis associated with 6-aminonicotinamide (6-AN) teratogenesis in rat embryos

Pregnant rats were injected ip with 6 mg/kg 6-aminonicotinamide (6-AN) at day 12 of gestation. Embryos removed between 1 and 48 h later had reduced adenosine triphosphate (ATP) concentrations, of about 50% of control values. All fetuses examined near term were malformed. Nicotinamide (NAM, 100 mg/kg) given ip 1 h after 6-AN afforded protection: malformations occurred in only 15% of the survivors; and there was minimal ATP reduction, 15% below control values. NAM given 2 and 4 h after 6-AN produced intermediate ATP concentrations and malformation frequencies. Thus, there was a relation between the embryotoxic and ATP-depressant actions of 6-AN in day 12 rat embryos.

Reproduction and teratogenesis: current methods and suggested improvements

The risks to human reproduction, particularly in regard to possible induction of birth defects, from present levels of environmental chemicals are thought to be low but in need of closer scrutiny than is now the case. Methods currently used to estimate the hazards to reproduction of new chemicals and drugs are reviewed and some shortcomings and potential sources of error are noted. Specific suggestions are made for improving existing methodology. In addition to the widely used treatment span encompassing all or most of the period of organogenesis, it is proposed that some exposure periods of shorter duration be added to avert possibly adaptative changes in maternal homeostatic systems. Greater diversity of test animals, beyond the rodent-rabbit species largely used today, is urged with the objective of better matching metabolic pathways in a test animal to those of man. The demonstration of an embryotoxicity effect-level must be regarded as essential in all tests, and once found this level should be used as the basis of extrapolating downward to find an acceptable tolerance level of dosage. More attention should be focused on postnatal functional evaluation after prenatal and perinatal exposure of test animals to environmental chemicals, especially those that might interfere with the maturation of the central nervous system, endocrine glands, and immunological mechanisms. The use of nonhuman primates should be reserved for the testing of drugs essential for use during human pregnancy or early pregnancy, because of the scarcity of such animals and the high costs of doing meaningful tests with them.

Reproduction and Teratogenesis: Current Methods and Suggested Improvements

The risks to human reproduction, particularly in regard to possible induction of birth defects, from present levels of environmental chemicals are thought to be low but in need of closer scrutiny than is now the case. Methods currently used to estimate the hazards to reproduction of new chemicals and drugs are reviewed and some shortcomings and potential sources of error are noted. Specific suggestions are made for improving existing methodology. In addition to the widely used treatment span encompassing all or most of the period of organogenesis, it is proposed that some exposure periods of shorter duration be added to avert possibly adaptative changes in maternal homeostatic systems. Greater diversity of test animals, beyond the rodent-rabbit species largely used today, is urged with the objective of better matching metabolic pathways in a test animal to those of man. The demonstration of an embryotoxicity effect-level must be regarded as essential in all tests, and once found this level should be used as the basis of extrapolating downward to find an acceptable tolerance level of dosage. More attention should be focused on postnatal functional evaluation after prenatal and perinatal exposure of test animals to environmental chemicals, especially those that might interfere with the maturation of the central nervous system, endocrine glands, and immunological mechanisms. The use of nonhuman primates should be reserved for the testing of drugs essential for use during human pregnancy or those likely to be taken inadvertently during early pregnancy, because of the scarcity of such animals and the high costs of doing meaningful tests with them.

Comparative distribution and embryotoxicity of hydroxyurea in pregnant rats and rhesus monkeys

Hydroxyurea was given to pregnant rhesus monkeys and pregnant rats in regimens adjusted to produce similar degrees of teratogenicity, for the purpose of comparing the distribution of the drug in the females and their embryos. According, in rats 137 mg/kg/day ip on days 9-12 resulted in a drug half-life in maternal plasma of about 15 min and in embryos about 85 min, after the last injection; and in monkeys 100 mg/kg/days iv on days 23-32 resulted in drug half-life in maternal plasma estimated to be 120 min and in embryos 265 min, after the last injection. Using as a baseline of biological effects the minimal concentration known to inhibit DNA synthesis in rat embryos and cancer cells, namely 10(-4) M, it was calculated that the rat embryos in the present study were exposed to this level or more for approximately 12 h whereas the monkey embryos were exposed for approximately 100 h. Although the teratogenic effects were not identical in the two species, these data are interpreted to mean that rat embryos are teratogenically much more sensitive to hydroxyurea than monkey embryos. These observations have important implications in the selection of appropriate species for tests to estimate human teratogenic risks. The rat, which is currently the most widely used animal for such tests, displays sizeable differences from rhesue monkeys, which is one of the animals thought to be most like man in teratogenic susceptibility.

DNA synthesis inhibition, cytotoxicity and their relationship to teratogenesis following administration of a nicotinamide antagonist, aminothiadiazole, to pregnant rats

Four groups of Wistar rats were treated with 100 mg/kg aminothiadiazole (ATD) i.p. on day 12 of gestation. The first group was allowed to proceed to day 20, when they were sacrificed and the teratogenic effects analyzed in the surviving fetuses. A second group was given 100 mg/kg nicotinamide (NAM) i.p. simultaneously or at intervals of 4, 8 or 12 h following ATD. Third and fourth groups corresponded to the first and second except that [3H]thymidine was administered and one uterine horn removed for histological study or analysis of DNA synthesis rates. The following observations were made:

1. ATD proved teratogenic to 90% of the surviving fetuses, causing one or more malformations of organs such as limbs, tail, palate and heart.

2. Nicotinamide was capable of protecting the embryo against ATD teratogenicity. This effect diminished as the interval between ATD and NAM administration lengthened so that by 12 h little protection remained.

3. ATD produced a severe and prolonged inhibition of DNA synthesis, reaching a low of 12% of control level at 17 h and returning to near normal by 38 h.

4. NAM reversed this inhibition of DNA synthesis in proportion to the length of the interval between ATD and NAM administration.

5. ATD produces severe cytotoxicity especially in the limb buds and neural tube.

6. Based on this and earlier studies the hypothesis is proposed that the time of appearance of maximal cell death plays a major role in determining the degree and pattern of forelimb ectrodactyly.