The effects of 13-cis-retinoic acid on the developing chick embryo were investigated. Fertilized eggs were injected via the yolk sac with single 50 microliters doses of either 1.5 micrograms, 15 micrograms, or 150 micrograms of 13-cis-retinoic acid in dimethyl sulfoxide on varying days of incubation (embryonic days 2, 3, 4, 5, or 6). Control embryos were given solvent alone or a mock injection. The embryos were examined on day 14 of incubation. The effects of retinoic acid on mortality and total malformations were both dose and developmental-stage responsive. The defects caused by 13-cis-retinoic acid occurred in mesenchymal tissues derived in part from the cranial neural crest ectomesenchyme. The craniofacial and cardiovascular malformations produced in the chick are analogous to those seen in animal models of retinoid teratogenesis and in human fetuses exposed to 13-cis-retinoic acid during maternal therapy for cystic acne. Following 13-cis-retinoic acid treatment, craniofacial and specific cardiovascular malformations were increased significantly compared to those in matched solvent and mock treated controls. The greatest number of malformations occurred when 13-cis-retinoic acid was given after cranial neural crest cell migration was complete. We propose that the primary effect of 13-cis-retinoic acid is on region-specific localization and differentiation of the mesenchymal subpopulation of cranial neural crest cells.

Moderately iron-deficient rats were significantly less susceptible to experimentally induced Proteus mirabilis pyelonephritis than iron-sufficient or severely iron-deficient littermates, as indicated by significantly lower prevalence of infection, mean pyelonephritic lesion scores, and numbers of P. mirabilis cells recovered from the kidneys.

In developing an avian model for 13-cis-retinoic acid (13cisRA) embryopathy, we found 13cisRA induced cardiovascular defects, especially Type I ventricular septal defects (VSDs) (Hart et al.: Teratology 41:463-472, '90). As the first step of investigating possible mechanisms, we have examined the light microscopic morphology of RA-induced cardiovascular defects in chick embryos. Fertilized eggs were injected via yolk sac with 150 micrograms 13cisRA in dimethylsulfoxide (DMSO), DMSO or mock injection on embryonic day 5 (E5). On E6, E7, or E8, surviving embryos were sacrificed and fixed in 10% formalin. Thoracic blocks were exised, embedded in paraffin and serially sectioned through the heart, base to apex. Slides were stained, screened for tissue orientation, then coded and evaluated without knowledge of treatment group. Examination of serial sections permitted qualitative evaluation of conotruncal ridge volume, mesenchymal organization, necrosis and extent of fusion. Extent of fusion was the only parameter influenced by 13cisRA treatment. On E6, ridge fusion was incomplete in all groups at comparable levels. On E7, ridge fusion in 13cisRA-treated embryos had not progressed as far proximally as in controls. By E8, there was a significant difference in the extent of fusion between 13cisRA-treated and non-RA-treated groups. We conclude 13cisRA-induced VSDs resulted from defective conotruncal ridge fusion and that the fusion defects did not result from decreased tissue volume, altered mesenchymal organization or increased necrosis.