Basal secretion remained stable up to seven days in culture. However, forskolin, ionomycin, ATP, phenylephrine, capsaicin, and bradykinin had no effect. Thus, PTHrP secretion appeared to be regulated by a protein kinase C-dependent pathway. PTHrP could also be demonstrated in pulmonary lavage liquid. Although the function of PTHrP in the adult lung is unknown, it could involve control of cell growth and differentiation or control of surfactant lipid secretion.
Further studies are necessary to elucidate the function of PTHrP in the lung.
This study shows that rat alveolar epithelial cells express immunoreactive CGRP also. The extracellular CGRP immunoreactivity eluted in the same fraction as rat CGRP- on high performance liquid chromatography. II cells was reversibly blocked by monensin, an inhibitor of secretory protein transport. CGRP secretion was stimulated in a concentration-dependent fashion by phorbol myristate acetate, but it was not affected by forskolin, capsaicin, bradykinin or nicotine. CGRP was not detected in culture media from alveolar macrophages or fibroblasts, potential contaminants of primary type II cell cultures.