A second possibility is that the whole ANF prohormone is being made in the lung and secreted directly into the pleural fluid. Pleural fluid originates from the lung rather than the pleura, and it is possible that both the N-terminus and C-terminus of the ANF prohormone are secreted simultaneously with this fluid into the pleural space. Now that the whole prohormone (ie, all 126 amino acids) has been found in pleural fluid, this possibility is even stronger than previously when only ANF was found in the pleural fluid. The presence of all 126 aa of the prohormone in pleural fluid plus evidence that perialveolar cells in lung express the ANF gene suggests that whole prohormone for ANF may be synthesized in the lung. Sirois and Gutkowsa have recently perfused the lungs of four human fetuses in vitro with oxygenated Krebs solution for 30 minutes and found ANF in the Krebs solution that had been perfused through the lungs suggesting that the lungs are capable of secreting ANF into the perfusate. Although these authors did not investigate whether the whole ANF prohormone or the 98 aa N-terminus of the prohormone was excreted into the perfusate, one would suspect from the data of the present investigation that the whole N-terminus as well as the C-terminus is secreted into the perfusate of isolated perfused lungs. buy flovent inhaler
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