Calcitonin as a marker for diethylnitrosamine-induced pulmonary endocrine cell hyperplasia in hamsters

Abstract

Immunoreactive calcitonin (iCT) has been localized in solitary endocrine cells and in clusters of these cells, called neuroepithelial bodies, in human and hamster lungs. It has been demonstrated that hyperplasia of hamster lung endocrine cells occurs following exposure to diethylnitrosamine (DEN), a systemic carcinogen. In the present study we have investigated iCT as a hormonal correlate of DEN-induced pulmonary endocrine cell hyperplasia in hamsters. Hamsters were given 3 mg of DEN per animal, subcutaneously, twice a week and then serially sacrificed at 2, 4, 8, and 12 weeks. By immunocytochemistry, iCT-containing cells could be demonstrated in thyroids, tracheal glands, and throughout the airway epithelium. At 8 or 12 weeks of DEN exposure, one to eight neuroepithelial bodies with iCT-containing cells were identified per square centimeter of lung sections, in contrast to zero to one neuroepithelial bodies/cm2 in control hamsters. By radioimmunoassay, pulmonary iCT increased significantly at 8 weeks of DEN exposure, amounting to 3.5-fold the control values at 12 weeks. Serum iCT increased at 4 weeks of exposure and by 12 weeks had tripled (183 +/- 62 pg/ml, mean +/- SD, p less than 0.001), as compared with control animals. Subsequently, DEN was stopped for 4 weeks, and the levels of both serum and lung iCT decreased, although they remained higher than those of controls. The serum and lung iCT of control hamsters was constant throughout the experiment (49 +/- 26 pg/ml and 1754 +/- 489 pg/gm of wet weight, mean +/- SD, respectively). Thyroidal iCT levels of exposed hamsters did not differ from those of the controls; both increased progressively. The DEN-exposed animals had retarded growth as compared with the controls. Column chromatography using superfine Sephadex G-75 demonstrated that both DEN-exposed and control lungs contained iCT with a predominant molecular size corresponding to the dimer of synthetic human calcitonin; whereas thyroidal iCT was mostly monomeric (approximately 3,500 daltons). The increase of pulmonary iCT correlates well with the 4-fold increase of pulmonary endocrine cells, reported earlier following similar DEN exposure. We conclude that iCT levels of hamster sera and lungs can be used as a biochemical parameter to monitor hyperplasia of the pulmonary endocrine cells in these animals.