Prolactin lowering activity of the retinoid Ro 14-9706 affecting lactation and pup survival

A preliminary investigation of high retinoic acid exposure during fetal development on behavioral competency and litter characteristics in newborn rats

Myelomeningocele (MMC) is the most common and severe type of spina bifida in which the developing spine and neural tube fail to close during prenatal development. This typically results in a small portion of the lower spinal cord and meninges protruding from the back of the individual, accompanied by severe motor and sensory deficits. In rats, retinoic acid (RA) exposure in high doses during fetal development has been shown to induce morphologic and clinical symptoms similar to humans with MMC. The aim of the current study was to examine litter characteristics and sensorimotor function in MMC-affected rat pups. Pregnant rats were gavage-fed 2 ml olive oil or all-trans RA (40, 45, 50 mg/kg) on gestational day 11. Pups underwent behavioral testing on postnatal day 2. Litter characteristics and newborn sensorimotor function varied across RA doses. Pups prenatally exposed to 45 and 50 mg/kg RA weighed significantly less than olive oil and 40 mg/kg RA pups. Litters exposed to 45 mg/kg RA suffered significantly higher mortality rates compared to other groups. Additionally, bladder function was significantly impaired in pups exposed to 40 mg/kg RA. Sensorimotor function findings demonstrated that for most behavioral assessments there was not a significant difference between control and RA-exposed subjects. However, pups treated with 40 mg/kg RA showed increased facial wiping, suggesting a hyper-responsiveness to sensory stimuli. Overall, the findings of the current study provide evidence for a model to examine litter characteristics and behavioral effects as well as morphology.

A behavioral and neuroanatomical investigation of the lethality caused by gestational day 11-13 retinoic acid exposure

In a companion article, we report that there is a sensitive period for all-trans retinoic acid (RA) lethality on gestational days (GD) 11-13. When dams were given 10 mg/kg RA daily for 3 consecutive days on GD 11-13, a number of pups were found dead in the home cage on the day of birth, and the remainder inevitably died due to an apparent inability to nurse. Here we report a set of experiments further investigating these effects. Dams were exposed PO to 10 mg/kg RA or oil vehicle on GD 11-13. Fetuses were removed by Cesarean section on the afternoon of GD 21, culled, and fostered to non-treated dams that had given normal vaginal delivery a day earlier. Maternal behavior was observed for the first 6 h after fostering. The next morning all surviving pups were given a brief behavioral evaluation, including the ability to attach to the nipple of anesthetized foster dams. At the time of C-section, culls were killed and brains were quickly removed and placed in fixative. A series of paraffin-embedded, cresyl-violet-stained serial sections of a representative brain stem from each litter was prepared. RA exposure did not increase fetal mortality. Treated litters were as large as controls, and virtually all treated fetuses were alive in utero. However, unlike controls, some treated fetuses appeared to have difficulty in initiating spontaneous breathing when delivered by C-section, and considerable physical stimulation was required before normal breathing began. As in the previous report, RA-exposed pups did not have milk in their stomachs after 18 h on the foster dam; further, they did not attach to the maternal nipple, and they had greater difficulty than controls in maintaining an upright posture. Examination of serial sections of the medulla indicated that the hypoglossal nucleus appeared grossly normal in the RA-exposed pups. In contrast, the inferior olive and the area postrema were affected by RA exposure. Both nuclei were normally located, but exhibited reduced cell density and/or intensity of staining. In the inferior olive the dorsal and principal nuclei were primarily affected, to the degree that about one quarter of treated brains had no identifiable principal nucleus. We conclude that RA exposure on GD 11-13 causes abnormal development of cell-dense regions of the medial medulla, and these abnormalities may account for the difficulty these animals experience in beginning spontaneous breathing and in nursing. These breathing and nursing problems in turn almost certainly account for the high mortality seen during natural birth and for the subsequent failure to thrive, respectively.

Comparative disposition, receptor affinity, and teratogenic activity of sulfon arotinoids

To investigate the relationship between sulfon arotinoid biotransformation and teratogenic activity, the potency of the ethyl (Ro 15-1570) and methyl (Ro 14-9706) arotinoid sulfones and their in vivo disposition in pregnant hamsters were studied. Administration of Ro 15-1570 was teratogenic, but Ro 14-9706 showed no such activity. Total absorbed doses of the ethyl and methyl sulfones (measured as maternal plasma AUC) were very similar. Total delivered dose of Ro 14-9706 to liver and lung was 120-160% that of Ro 15-157, and Ro 14-9706 was transferred in greater amounts to the embryo as well. Placenta AUC for parent sulfon arotinoids was 160-250% that in the embryo. Plasma analyses by HPLC suggested that the ethyl sulfone was oxidized and appeared in maternal plasma as the corresponding sulfinic (Ro 14-9572) and sulfonic (Ro 14-3899) acids, amounting to 10% and 16%, respectively, of the mean maternal ethyl sulfone Cmax value. The concentrations of sulfinic and sulfonic metabolites were always less than the analytical limit of detection in placenta and embryo after maternal ethyl sulfone intubation. Neither the sulfinic nor the sulfonic acid were ever detected in maternal circulation, placenta, or embryo after methyl sulfone intubation. Comparisons of their binding affinities found that neither the ethyl nor the methyl arotinoid sulfone could act as a ligand for cellular retinoic acid-binding protein (CRABP), nor could these compounds bind retinoid nuclear receptors (RAR). Transcriptional activation of RARs was weak and similar for both compounds. The sulfinic and sulfonic acid arotinoids bind and transactivate RARs, and bind CRABP with efficiencies similar to all-trans-retinoic acid. Furthermore, they are active in cultured limb bud chondrocytes. The results suggest that the methyl sulfone (in accord with its lack of activity in cultured limb bud chondrocytes) is of no toxicologic significance in hamster embryo--even after relatively high delivered dose. Teratogenicity of the ethyl sulfone (which shows marked inhibition of chondrogenesis in cultured limb bud) does not appear to depend on measurable concentrations of these sulfinic/sulfonic acid metabolites in the hamster embryo.