Comparative Study of the Binding of Prolactin and Growth Hormone by Rabbit and Human Lung Cell Membrane Fractions

The specific binding capacities for human prolactin (hPRL) and human growth hormone (hGH) were examined in human lung membrane preparations at different developmental stages. A parallel study was carried out on rabbit lung preparations to compare binding parameters. Lung tissues were obtained from 15 fetuses of 16–38 weeks after spontaneous or therapeutic abortion and from 7 adults (lobar resection surgery). A histological study was systematically performed with a radial alveolar count in the fetuses with suspected hypoplasia. Binding analysis was performed on both intact membrane preparations and MgCl<sub>2</sub>-treated membranes, using [<sup>125</sup>I]hGH and [<sup>125</sup>I]hPRL as tracers. In the rabbit lung, specific [<sup>125</sup>I]hGH binding was found. Scatchard analysis revealed a single class of binding sites (affinity constant: 2.6 ± 0.8 × 109 l/nmol and number of binding sites: 9.5 ± 4.3 fmol/mg protein for adult rabbit; 1.85 ± 0.5 × 10<sup>9</sup> l/nmol and 27.6 ± 3.0 fmol/mg protein for 25-day-old rabbit fetuses, respectively). In contrast, [<sup>125</sup>I]hPRL did not specifically bind to lung membrane preparations. In the human lung, no consistent specific binding sites for [<sup>125</sup>I]hPRL or [<sup>125</sup>I]hGH (< 0.5 %/mg protein) were detected in adults and in 11 of the 15 fetuses. In 4 fetuses, little specific binding was observed (0.59-1.9%/mg protein) for [<sup>125</sup>I]hGH and (1.5%/mg protein) for [<sup>125</sup>I]hPRL. There was no correlation with histological lung structure. Our findings confirm the presence of specific binding sites for GH in the adult rabbit lung and demonstrate such binding in the fetal rabbit lung. In contrast, our results showed no significant binding for PRL and GH in the human lung, suggesting that these hormones do not play a direct physiological role in human lung growth and maturation.