Fetal Alveolar Epithelial Cells Contain [d-Ala2]-Deltorphin I-like Immunoreactivity

Opiate-like peptides can regulate many cellular functions. We now map [d-Ala2]deltorphin I (DADTI)–like immunoreactivity (DADTI-LI) in developing mouse lung and analyze potential functional roles. Most DADTI-LI–positive cells were alveolar cells negative for prosurfactant protein (proSP)-C immunoreactivity. Peak numbers of DADTI-LI–positive cells occurred on embryonic Day 18, decreasing postnatally. To analyze developmental effects of DADTI, e17-18 lung explants were treated with [d-Ala2]deltorphin II (DADTII, soluble DADTI analogue, δ -receptor–specific) versus dermorphin ( μ -receptor–specific). Type II pneumocyte differentiation, assessed by [3H]choline incorporation into saturated phosphatidylcholine and proSP-C immunostaining, was inhibited by DADTII but stimulated by dermorphin. Cell proliferation, measured as [3H]-thymidine incorporation and proliferating cell nuclear antigen immunostaining, was stimulated by DADTII and inhibited by dermorphin. All effects were dose-dependent. DADTII-inhibited chol...