Abstract
The following three experiments were performed to determine the effects of N-acetyl-L-cysteine (NAC) on the quantity and quality of respiratory tract fluid (RTF) and sputum. All drugs used were administered into the stomach through a gastric tube. 1) Indirect measurement of bronchial secretion in rats, which was expressed by the amounts of dye excreted into the respiratory tract, was carried out according to the Sakuno's method, with some modification. Some expectorants of the secretomotor type, such as bromhexine and pilocarpine, significantly increased the secretion, even at low doses. On the other hand, mucolytic agents such as NAC augmented the secretion only in doses of 500 to 1500 mg/kg. 2) As a direct method of measurements, Kasé's modification of Perry and Boyd's method was used to collect RTF, quantitatively, from rabbits. The RTF of healthy rabbits was colorless and watery. The administration of NAC in doses of 500 to 1500 mg/kg augmented the output volume and RTF became slightly turbid, probably due to an increase in the viscous mucus. 3) Rabbits with subacute bronchitis were prepared by long-term exposure to air contaminated with SO2 gas and sputa were collected before and after administration of NAC, respectively, according to the Kasé's method. The sputa were opalescent and viscous gel included nodular masses. The administration of NAC, 1000 and 1500 mg/kg resulted in a dose dependent decrease in the relative viscosity. The percent-decrease in viscosity with NAC was statistically correlated with that in amounts of dry matter, those in protein and polysaccharide in the sputa. From the results described above, it was concluded that NAC given into the stomach can liquefy sputum by splitting mucoprotein disulphide linkages, that is, altering the rheological characteristics of sputum to facilitate expectoration.
