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.

Active transport of polypeptides in rabbit nasal mucosa: possible role in the sampling of potential antigens.

Transepithelial pathways of macromolecule transport have been studied in vitro in rabbit nasal respiratory mucosa, maintained at 27 degrees C. Transepithelial electrical potential difference, short-circuit current and resistance were 3.4 +/- 0.5 mV (submucosa positive), 65.0 +/- 6.7 microA cm-2 and 52.1 +/- 5.6 omega cm-2 respectively (n = 15). These electrical characteristics are those of a leaky epithelium allowing macromolecules to permeate paracellularly. A detailed permeation study of a polypeptide (elcatonin, Mw = 3362) was also undertaken. Elcatonin mucosa-submucosa (Jms) and submucosa-mucosa (Jsm) fluxes were measured by radioimmunoassay. With 10 micrograms/ml elcatonin, Jms was significantly larger than Jsm for the whole 120-min period of observation; net flux showed a maximum in the first 30 min (Jms = 13.6 +/- 1.0 ng cm-2 h-1, Jsm = 1.4 +/- 0.1 ng cm-2 h-1, n = 10). Jms fell towards the value of Jsm if the temperature was reduced to 4 degrees C or if the mucosa was simultaneously treated with 0.1 mM dinitrophenol and 3 mM monoiodoacetate. Jms and Jnet followed saturation kinetics with increasing elcatonin concentrations. Adrenocorticotropic hormone (Mr = 4500) produced a similar pattern to elcatonin. However, Jms and Jsm were not significantly different from each other at any time either for [3H]sucrose (Mw = 342) or for [14C]polyethyleneglycol-4000 (Mw = 4000) when present in the bathing medium at 500 microM concentration. The results show active transport of polypeptides in parallel with passive permeation (possibly through leaky intercellular junctions). Active transport does not appear to be related to nonspecific pinocytosis but to receptor-mediated endocytosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Transepithelial electrophysiological parameters in rabbit respiratory nasal mucosa isolated in vitro.

1. Transepithelial electrical p.d. (Vms), short circuit current (Isc) and transepithelial resistance (Rep) were determined in rabbit nasal mucosa and were compared with the equivalent parameters of human nasal mucosa. 2. Vms was about 1 mV (submucosa positive) in the absence of glucose, but increased continuously in the presence of glucose. Since Isc also increased in parallel and Rep remained constant (about 40 omega cm2), glucose effect was to power pumping. 3. Diffusion potentials raised by reducing luminal Cl- or Na+ or Cl- and Na+ concentrations were also measured and compared with values obtained in trachea and gallbladder. 4. Evidence is produced, with sounder basis than in trachea, that junctional pathways in airway epithelia are lined with fixed positive charges (which make anions more permeable than cations), unlike junctional pathways of the gastrointestinal tract which are lined with fixed negative charges.

[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.

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.