The factors that regulate elastin synthesis during pulmonary alveolar septal formation have not been identified. Because maximal alveolar elastin synthesis occurs over a relatively brief period (postnatal days 4-14 in the rat), we hypothesized that changes in the local concentrations of factors that regulate elastin synthesis may precede or accompany this period. Because pulmonary retinoid stores decline just before the fourth postnatal day, we also hypothesized that this decline could be accompanied by the utilization of retinoic acid, one of the most biologically active retinoids, in a regulatory process that increases elastin synthesis. If these hypotheses are correct, then retinoic acid should increase elastin synthesis by pulmonary cells. Therefore, cultures of neonatal rat lung fibroblasts were exposed to retinoic acid, and elastin production was quantitated. Retinoic acid produced a two- to threefold increase in the steady-state level of elastin mRNA, in soluble elastin, and in insoluble elastin. The transcriptional initiation rate of the elastin gene was 1.8-fold higher in nuclei that were isolated from retinoic acid-treated cells than in nuclei that were isolated from control cells. This indicates that the increase in steady-state elastin mRNA results, at least partially, from an increase in elastin transcription. Lung fibroblasts that were isolated from 8-day-old rats, but not cultured, contained retinoic acid. These findings suggest that retinoic acid is a potential regulator of elastin synthesis in developing pulmonary alveoli.

Human fibroblasts and A431 human epidermoid carcinoma cells were cultured on gamma-irradiated human amnion collagen as well as on plastic dishes and non-irradiated collagen coated dishes. The morphology, attachment, growth and short-term cytotoxicity of these culture conditions have been determined. Both irradiated and non-irradiated amnion collagen enhanced the attachment and proliferation of fibroblasts as compared to the plastic dishes. No differences in these properties were observed for A431 cells cultured on irradiated collagen when compared with culture on non-irradiated collagen substrates. Cytotoxicity assays showed that irradiated and non-irradiated collagens were not cytotoxic for either fibroblasts or A431 cells. The results demonstrated that amnion collagen irradiated at doses of 0.25-2.0 Mrads is optimal for cell growth.