摘要：Uptake of cadmium into the lung and chemical forms in the lung supernatants of rats were studied after intratracheal instillation of cadmium chloride to find the mechanisms why the lung is sensitive to the metal by exposure through the airways. Male Wistar rats (10 weeks old ; body weight, approximately 270 g) were instilled intratracheally with cadmium chloride at a dose of 2.5 μg Cd/rat (0.4 ml in physiological saline). The animals were killed 1/6, 1/3, 2/3, 1, 2, 3, 6, 12, 24 and 48 h after the instillation. The lungs were homogenized in the same volume (w/w) of 0.1 M Tris-HCl buffer (pH 7.4, 0.25 M glucose ; bubbled through with nitrogen gas) using a Polytron homogenizer in an atmosphere of nitrogen gas after removing air in the lungs under reduced pressure. More than 90% of cadmium was retained in the lung 10 min after the instillation. However, the concentrations of the metal in the supernatants (170000 g for 60 min) were less than 50% in the homogenates before 12 h after the instillation. The supernatants were subjected to analysis for the distributions of cadmium, copper, iron, phosphorus, sulfur and zinc by high performance liquid chromatography-inductively coupled argon plasma-atomic emission spectrometry (HPLC-ICP). Cadmium bound to metallothionein was less than 50% in the supernatants within 12 h after the instillation. Two distinct cadmium peaks were observed other than metallothionein on an Asahipak GST-520 column by HPLC-ICP within 3 h after the instillation. The rapid uptake into the lung and low inducibility of metallothionein in the lung may explain the high susceptibility of the lung to cadmium.
