Content, in vivo release, and bioactivity of fetal pulmonary immunoreactive adrenocorticotropin

We hypothesized that fetal lung contains and releases immunoreactive (ir) adrenocorticotropin (ACTH). Fetal sheep lung (89-145 days gestation, n = 13) irACTH content was 4,100 +/- 672 (SE) pg/g lung wet wt compared with 5,425 +/- 1,403 (SE) pg/g in adults (n = 5) when measured by radioimmunoassay (RIA). irACTH values normalized to protein content were 158 +/- 18 and 95 +/- 22 (SE) ng/g protein for fetuses and adults, respectively. Grouped by age, < 90 days (n = 4), 131-139 days (n = 5), and 143-145 days (n = 4), the values for irACTH were 184 +/- 28, 173 +/- 33, and 114 +/- 33 (SE) ng/g protein, respectively, and declined significantly from < 90 days to adulthood. RIA serial dilution curve slopes were different from standard in 7 of 13 fetuses and in all adults, suggesting that irACTH structure differs from ACTH-(1-39). Acute in vivo fetal pulmonary artery and vein sampling (n = 5, 120-128 days gestation) revealed a mean difference of -609 +/- 476 (SE) pg/ml, a statistically significant release of irACTH across the lung. Western blotting revealed that pulmonary irACTH migrates in multiple immunostaining bands between molecular weight 14,000 and 46,000 and does not colocalize with ACTH-(1-39). Adrenal cell bioassay revealed that pulmonary irACTH is not corticotropic. We concluded that ovine fetal lung contains large-molecular-weight irACTH, that content declines from 90 days gestation to adulthood, and that, under acute conditions, the fetal lung releases irACTH substances in sufficient quantity to contribute to circulating hormone concentrations of irACTH.