The in vitro porcine brain tubulin assembly assay: effects of a genotoxic carcinogen (aflatoxin B1), eight tumor promoters and nine miscellaneous substances.

Aflatoxin B1 (AFB1) had a reversible inhibitory effect on the assembly of porcine brain tubulin in vitro. The 30%-inhibition concentration was 0.3 mM AFB1. The 8 tumor promoters showed different effects. Five of them, anthralin, cholic acid, gamma-hexachlorocyclohexane (lindane, gamma-HCH), lithocholic acid and phenobarbital (PB), enhanced the in vitro assembly. The effect was reversible in the case of PB and anthralin, only partially reversible in the case of cholic acid and gamma-HCH, whereas the stimulating effects of lithocholic acid led to an irreversible modification of the tubulin structure, as shown by the insolubility of the microtubules at 0 degrees C. This could be confirmed by an electron microscopic study. The doses necessary for a 30% enhancement of the steady-state level were 3 mM (PB), 0.2 mM (anthralin), 6 mM (cholic acid), 0.7 mM (gamma-HCH) and less than 0.2 mM (lithocholic acid). The other 3 tumor promoters tested - diethylstilbestrol (DES), 4,4'-dichloro-diphenyl-trichloro-ethane (DDT) and saccharin - inhibited the assembly. The concentrations necessary for a 30% inhibition varied within a wide range: 0.025 mM, 0.4 mM and 7.5 mM for DES, DDT and saccharin, respectively. Five of the 9 miscellaneous compounds, namely asbestos (crocidolite), bavistan, colchicine, chloropropham and ethylacetate, showed inhibitory effects, whereas Fe2+ (a constituent of asbestos) and 5-azacytidine did not influence the assembly process. The 30%-inhibition concentrations for colchicine, ethylacetate and asbestos were 10 microM, 0.153 M and 0.19 mM, respectively. For bavistan and chloropropham the 30%-inhibition values were 0.7 mM and 2.0 mM, respectively. The inhibitory effects of chloropropham and asbestos were reversible. For colchicine and bavistan the reversibility of the effects was not assayed. In agreement with published data, dimethylsulfoxide (DMSO) and acetone enhanced the in vitro assembly of porcine brain tubulin. The doses needed for a 30% enhancement by DMSO and acetone were 0.4 mM and 0.136 M, respectively. The effect of DMSO was irreversible whereas acetone led to a reversible stimulation. Some compounds were tested for their influence on preformed microtubules (interaction with the equilibrium between assembly and disassembly). Anthralin, cholic acid, PB and DMSO showed no effect on the steady-state plateau. A slight reduction was induced by DDT and bavistan, whereas DES, colchicine and chloropropham led to a pronounced reduction.

The ontogeny of the mouse estrogen receptor: the pelvic region.

The appearance of estrogen receptors was examined during the course of fetal and neonatal development in the pelvic region of the mouse; 3H-diethylstilbestrol (DES) was administered via the maternal circulation to developing mice on days 4, 7, 10, 13, 14, 15, and 17 of gestation or to neonates on the day of birth. Localization of the ligand was monitored autoradiographically. The earliest appearance of estrogen receptors occurred in the mesenchyme around the genital ducts on day 13 of pregnancy. On subsequent days, estrogen-concentrating cells appeared in certain mammary-gland cells, connective-tissue strands, in perichondrium associated with specific developing bones, skin, interstitial tissue of the testis, in a sheath of cells surrounding the colon, and in the urethra. The significance of cells containing estrogen receptors in these locations is discussed in reference to a transplacental action of estrogens and the clinical ramifications of DES.

The ontogeny of estrogen receptors: brain and pituitary.

This study examines the prenatal and neonatal development of estrogen receptors in the central nervous system of the mouse. [3H]Diethylstilbestrol (DES) was injected into pregnant mice on days 4, 7, 10, 13, 14, 15 and 17 of gestation or into neonates. DES is an estrogen agonist that circumvents the alpha-fetoprotein barrier, thereby gaining access to intracellular estrogen receptors. Sixty minutes after injection whole embryos, fetuses or neonates were rapidly frozen and processed for autoradiography. Although the transplacental movement of the isotope was confirmed in all age groups evidence for nuclear estrogen receptors was not seen in the brain until day E14. On this day a few labeled cells first appeared in the basal hypothalamus, preoptic area, amygdala, midbrain and spinal cord. The number and the labeling intensity of target cells increased in each of these areas on days E15, E17 and P0. The first appearance of estrogen receptors closely follows the reported birthdates of neurons in these regions.

Ultrastructural study of the mucification of the stratified epithelium of the mouse vagina.

After transplacental treatment of mice with estrogens, a heavy mucification was found in the fornices of the vaginae of the offspring. The resulting mucified stratified epithelium is described by light and electron microscopy. It consists of two different cell types: cells forming mucus on top of cells forming tonofilaments. Mucus formation is usually attributed to treatment with progestagens, or with the estrogens combined with vitamin A. Estrogen treatment per se has been shown to be responsible for tonofilament formation. Our unexpected findings are discussed against the background of different theories of development of vaginal epithelium as well as their possible interpretation as beginning of adenosis.

Model systems for cardiotoxic effects of anthracyclines.

The use of anthracycline antibiotics in cancer chemotherapy is limited by their cardiotoxic qualities. For the evaluation of new derivatives animal model systems are required. Cardiomyopathy can be induced in rabbits and monkeys, but these models are too expensive for screening purposes. In rats, anthracycline antibiotics cause morphologic lesions of the heart muscle, but these are more difficult to demonstrate than in larger animals. However, significant changes of the heart function (electrocardiogram (ECG), cardiac output), the function of heart mitochondria (inhibition of electron transfer, uncoupling of oxidative phosphorylation and inhibition of Ca translocation) occur in a dose-related manner. Intraventricular conduction defect demonstrated in the ECG is one of the earliest and most consistent expressions of the cardiotoxic properties of anthracyclines. It was therefore used as primary screening parameter. The results of the screening of over 50 new anthracyclines has shown that the cardiotoxic properties vary considerably and that they are not closely related to the chemotherapeutic and the hematotoxic properties. Interesting structure-activity relationships were observed in a series of rubidazone derivatives substituted at the benzhydrazone part of the molecule.