Effects of atrial natriuretic peptide on type II alveolar epithelial cells of the rat lung. Autoradiographic and morphometric studies.

Effects of atrial natriuretic peptides (ANP) on Type II cells of the rat lung were examined, using autoradiographic and morphometric techniques. The injection of an excess of ANP, together with [125I]ANP, significantly inhibited the uptake of radioactive ANP in the lung tissue. Following autoradiography, silver grains of [125I]ANP labelled Type II cells, endothelial cells and smooth muscle cells of vessels, bronchi and bronchioles. As for morphometric changes in subcellular structures of Type II cells after the injection of ANP, the volume and surface densities of the rough endoplasmic reticulum increased at 15 minutes, while those of the Golgi complex increased from 5 minutes, peaking at 30 minutes. At 15 minutes the volume and surface densities of mitochondria significantly increased. The volume and surface densities of multivesicular bodies with an electron-dense matrix also increased from 15 minutes after the injection. Lamellar bodies showed decreased volume and surface densities at 15 minutes whereas the densities showed an increase at 30 minutes and were higher at 60 minutes than those in the control. These results suggest that Type II cells provide a binding site for ANP which facilitates the production of lamellar bodies in addition to their secretion.