Bronchoalveolar lavage (BAL) has been performed in 22 healthy nonsmoking male volunteers after exposure to 8 ppm SO2 (20 mg/m3). The exposure level exceeds the US Short-Term Exposure Limit (STEL) of 5 ppm, but occurs as peak exposures in industrial indoor environments. Exposures were made during light work on a bicycle ergometer in an environmental exposure chamber for 20 min. BAL was performed 2 wk or more before exposure and 4, 8, 24, and 72 h after exposure in eight subjects at each time interval. Four hours after exposure significant increases were found in the numbers of lysozyme-positive macrophages, lymphocytes, and mast cells (p less than 0.02 to 0.05). Lymphocytes, lysozyme-positive macrophages, total count of alveolar macrophages, and total cell number increased to peak values 24 h after exposure (p less than 0.02 to 0.05). Seventy-two hours after exposure the cell numbers and distribution had returned to normal. The time course of the cell reactions found in BAL fluid after controlled SO2 exposure represents a new and previously not reported response to a noxious gas.

The effect of cadralazine and its active metabolite CGP 22639 on the covalent binding reaction of C4 and C3 has been studied. Trypsin-Sepharose was used to activate radio-labelled C3 and C4 and binding of the radio-labelled protein to the trypsin-Sepharose was measured. Cadralazine inhibited 50% of the binding of C3 and C4 at concentrations of 19 mmol/l and 15 mmol/l, respectively. Its active metabolite was more potent and inhibited 50% of the C3 and C4 binding at concentrations of 8 and 3.5 mmol/l, respectively. These concentrations are much higher than those found in plasma during therapy. This is consistent with the clinical observation that in patients with normal kidney function cadralazine is not an inducer of SLE.

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