Genotoxicity of hormonal steroids.

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

The effects of chlorpromazine, mianserin and Org GC94 on reproductive function in the rat.

In the assessment of drug safety with respect to mammalian reproductive function chlorpromazine and two serotonin antagonists, mianserin (Org GB94 ) and Org GC94 were studied for their effects on ovulation and ovum transport. In addition, the effect of coitus on drug-induced ovulation inhibition was investigated. The compounds were intragastrically administered to Charles River CD rats in a single dose or in consecutive daily doses for one or two weeks. The incidence of ovulation and the number of eggs were recorded. The compounds blocked ovulation in pro-oestrous rats after a single dose. Ovulation was restored by coitus in drug-treated animals. The compounds appeared to become less effective in blocking ovulation after multiple dosing. No effects on ovum transport were detected. From the results obtained in this study, it is concluded that the CNS-active drugs investigated did not adversely affect reproductive function in the rat.

Criteria for the standardization of Salmonella mutagenicity tests: results of a collaborative study. II. Studies to investigate the effect of bacterial liquid culture preparation conditions on Salmonella mutagenicity test results.

The influence of various parameters and growth conditions in the "overnight culture" of Salmonella typhimurium strains on mutagenicity test results was investigated. A number of factors were first suspected to be of some importance for the quantitative outcome of the mutagenicity test. None of them, however, was found to influence the results to such a marked extent as to be a major source of variability. Only the brand of nutrient broth used for the propagation of the bacteria proved finally to have a certain effect on the number of (spontaneous and induced) revertant colonies, although no precise and quantitative statements can be made with regard to a possible standardization of this experimental segment in the Salmonella mutagenicity test. The occurrence of such unpredictable but noticeable influences is, however, evidence for the importance of an intralaboratory optimization and standardization of all parts of the test procedure.

Splayleg: a spontaneous limb defect in rabbits. Genetics, gross anatomy, and microscopy.

A limb defect in rabbits known as splayleg arose in a closed breeding colony of Dutch rabbits. Since the causes of this postural deformity are not fully understood, an effort was made to clarify the mode of inheritance and the etiology of the disease. Pedigree analysis and genetic mating tests showed that, in contrast to published reports, the disease is not determined by a single recessive gene with complete expressivity. The underlying genetic system is composed of one recessive gene with reduced expressivity or of more genes with the probable involvement of environmental factors. Femurs of abnormal limbs displayed endotorsion of the shaft and anteversion of the neck as the main features. Endotorsion of the femur was associated with exotorsion of the tibia. Dislocation of the hip was not observed. There was no abnormnal laxity of the joint capsule or the ligamentaum teres. Only minor differences in the acetabulum between control and splayleg rabbits were observed. Enzyme histochemistry and electron microscopy of the gluteus medius, adductor longus- and magnus, sartorius, gracilis, and semitendinosus muscles and the femoral, peroneal, and tibial nerves did not reveal any qualitative differences between splayleg and control rabbits. A study on muscle fiber diameter showed that fibers of splayleg animals were in general smaller, particularly in the semitendinosus. Atypical mitochondria of muscles were observed in all rabbits, but more frequently in splayleg animals. A hypothesis is presented in which imbalanced development of the neural, muscular and skeletal systems of the limb is the primary defect. This results in torsion of the femur. It depends on the degree of femoral torsion and the capacity of the young rabbit for compensation by exorotation of the limb in the hip whether a persistent splayleg posture will develop.

Mutagenicity studies with o-tolidine and 4,4'-tetramethyldiaminodiphenylmethane.

This paper confirms the mutagenicity of 2 carcinogenic chemicals, o-tolidine and 4,4'-tetramethyldiaminodiphenylmethane (TDDM). o-Tolidine and TDDM were both tested in the Salmonella/mammalian-microsome test and in the sister-chromatid exchange (SCE) test with rabbit lymphocytes in vitro. The number of revertants was increased in the presence of S9 mix by o-tolidine in the Salmonella typhimurium strains TA98 and TA1538, and by TDDM in strains TA98 and TA100. Both compounds showed weak SCE-inducing activity in cultured rabbit lymphocytes in the absence, but not in the presence, of an exogenous metabolic system.

Cysts in rabbit foetal brains. Malformation or artefacts?

Reports have appeared in the literature on brain cysts in rabbit foetuses. This paper reports on investigations carried out to assess whether "cystic dilatation" is a malformation or an artefact. The results show that "cystic dilatation" arises by splitting of the pia-arachnoid membrane leading to a space between the skull and the neural tissue which is lined by the pial layer on its interior aspect and the arachnoid on its exterior aspect. The evidence presented indicates that "cystic dilatation" is a fixation-induced artefact. In addition, the presence of several artificial tissue clefts and spaces in preserved rabbit foetal brains is reported.

Sister-chromatid exchanges induced in vitro by cyclophosphamide without exogenous metabolic activation in lymphocytes from three mammalian species.

The induction of sister-chromatid exchanges (SCEs) by cyclophosphamide (CP) in human, rat and rabbit lymphocytes was studied in vitro without exogenous metabolic activation. In contrast with published reports, CP induced SCEs in lymphocytes from all three species, indicating that cultured lymphocytes possess the metabolic capacity to convert this indirect-acting mutagen.

The role of the pituitary-ovarian axis in the termination of early pregnancy in rabbits treated with ethinyl-oestradiol.

The pathogenesis of embryonic death following maternal treatment with ethinyloestradiol was investigated. Pregnant rabbits received daily oral doses of 0.4 mg/kg body weight of ethinyloestradiol starting on day 6 of pregnancy. Dams were autopsied after 3, 6, or 9 days of treatment. Uterine swellings, ovaries, and the pituitary gland were examined using histochemical techniques. The results showed that in the treated animals there were morphological signs indicating decreased secretory activity of gonadotrophin and prolactin producing cells of the pituitary gland, luteolysis, and embryonic death within the first few days of treatment. The present study indicated that termination of early pregnancy in rabbits is most probably due to the interference of ethinyloestradiol with the pituitary-ovarian axis which in turn results in luteolysis and impairment of luteal steroid synthesis.

Development of the obese-hyperglycemic syndrome in mice with a growth hormone deficiency.

By mating mice heterozygous for the recessive gene, obese (ob/+) (+/+), with mice homozygous for the recessive gene, dwarf (+/+)(dw/dw), and subsequent mating of the offspring, mice homozygous for both the obese and dwarf gene were obtained. It was established that the genes for obese and dwarf mice belong to different linkage groups. The homozygous obese dwarf mice develop obesity and hyperinsulinemia. The degree of hyperglycemia developed by these homozygotes is not significantly different from that of nonobese dwarf mice. Because homozygous dwarf mice are deficient in growth hormone production, it was concluded that obesity and hyperinsulinemia can develop under conditions of extreme growth hormone deficiency.