Developmental toxicity during the preimplantation period: embryotoxicity and clastogenic effects of chlorambucil in the rat.

To evaluate the toxicological effects of chemicals on preimplantation mammalian embryos, pregnant rats were treated with chlorambucil (0, 3, 6, and 12 mg/kg IP) on day 1, 2, or 3 of gestation (positive vaginal smear = day 0). Blastocysts were collected on day 4 and evaluated for gross morphology, cell number, and mitotic index. Some females treated on day 3 post coitum were sacrificed on day 20 and fetuses were evaluated for teratogenic effects. On day 4 of gestation a dose-related reduction of cell number/embryo was recorded; this effect was most manifest with treatment on day 3 post coitum. The mitotic index was significantly higher in all treated groups. A dose-related increase in "micronucleus-like bodies" has been observed in treated embryos. A comparison with the micronucleus test in the bone marrow revealed a major sensitivity of the embryonic material. No malformations have been observed in fetuses at term, but their weights were significantly reduced and a dose-related increase of postimplantation loss was recorded in treated females.

Embryotoxic effects of 5-hydroxytryptamine during the peri-implantation period in the rat.

Administration of 5-hydroxytryptamine creatinine sulphate (5-HT) 5-10-20 mg/kg s.c. to pregnant rats during the preimplantation period (1200 h, Days 1 through 5) did not inhibit implantation. Experiment 2: Administration to pregnant rats during the peri-implantation period (0900 h, Day 6) of 5-HT 5 mg/kg s.c. did not affect implantation or embryo-fetal development. 5-HT 10 mg/kg s.c. produced a significant increase (P greater than 0.01) in the resorption rate (31.8%) and severe cardiovascular or ophthalmic malformations in 5.3% of viable fetuses. 5-HT 20 mg/kg produced a resorption rate (97.2%) virtually incompatible with the continuance of pregnancy. Experiment 3: Histological examination of uterine preparations made from Day 6 pregnant rats sacrificed 6, 24, and 30 h after receiving 5-HT 20 mg/kg s.c. showed, in 30 h post-injection preparations, toxic effects at implantation sites (uterine lumen completely deprived of epithelial layer and filled with cellular debris, and complete degeneration of implanted embryos) but no toxic effects between implantation sites. Experiment 4: Administration of 5-HT 10 mg/kg s.c. to pregnant rats during the postimplantation period (Days 10 and 11) produced a 63.2% resorption rate, a reduction in the mean weight of viable fetuses, and severe malformations in 24% of viable fetuses. The embryotoxic activity of 5-HT may be attributed to its vasoconstrictive action which renders the uterine mucosa or trophoblast ischemic, thus causing irreversible damage to the luminal epithelium at the implantation sites.

Hydroxyurea as a reference standard in teratological screening. Comparison of the embryotoxic and teratogenic effects following single intraperitoneal or repeated oral administrations to pregnant rats.

The antimitotic drug hydroxyurea (HU) has been evaluated as a positive standard for teratological screening in rats. Single intraperitoneal administration of HU to pregnant Sprague Dawley rats at the dose level of 750 mg/kg induced embryolethality or specific anomalies depending on the day of treatment: HU administration on days 7, 8, 9, 10 or 11 produced lethal effects in a high percentage of embryos; cardiovascular malformations were specifically induced by a single dose on day 10, ocular anomalies on day 10 or 11, palatoschisis or diaphragmatic hernia on day 12, limb or paw deformities on day 10, 11, 12 or 13. This experiment demonstrated the high susceptibility of the genotype of our colony of rats to the embryotoxic potential of HU. Repeated oral administration of HU during the organogenetic period (from day 6 to day 15 of gestation), at dose levels ranging from 50 to 450 mg/kg, led to a dose dependent embryolethal and teratogenic effect. Live foetuses at term generally showed severe ocular and craniofacial anomalies; hydrocephalus, cardiovascular anomalies, vertebral and costal defects were also registered. Limb malformations were not frequent and paw abnormalities were totally absent. In our experimental conditions, the dose level of 300 mg/kg is regarded as a suitable positive control dosage in teratological testing of new molecules by oral route.

The extent of fetal ossification as an index of delayed development in teratogenic studies on the rat.

In teratogenic studies toxic effects may manifest themselves in retarded fetal development, such as a reduction in fetal weight. In searching for an additional index, the number of centers of ossification in seven skeletal districts (sternum, metacarpus, metatarsus, cervical and caudal vertebrae, anterior and posterior proximal phalanges) of rat fetuses delivered on days 19, 20 and 21 of gestation were counted and compared. Results showed uneven ossification in day-19 and -20 fetuses, but sufficiently advanced, homogeneous and uniform ossification in day-21 fetuses to provide a reliable quantitative index for evaluating retarded fetal development. It is therefore proposed that the stage of skeletal ossification in day-21 fetuses be used in teratogenic studies in the rat to evaluate retarded fetal development.

[Effect of glycerol formal on the embryonic development of the rat]. / Effetti del glicerolformale sullo sviluppo embrionale del ratto.

In order to evaluate the effect on embryonic development of a solvent commonly used in pharmacological investigations, glycerol formal was administered to pregnant rats from days 6 through 15 of gestation at the daily doses of 0.25, 0.50 and 1.0 ml/Kg i.m. Glycerol formal did not induce systemic toxicity in the mothers, but showed an embryotoxic and teratogenic activity on the products of conception.