Metabolic fate of nitric oxide

Summary The metabolic pathway of inhaled NO in rats was investigated with ¹⁵NO. After ¹⁵NO exposure, the content of the ¹⁵N (atom % excess) in blood, red cells, serum, each organ tissue (perfused with saline solution) and urine were estimated. The contents of ¹⁵N in the samples of blood, serum, red cells, and urine were relatively high and those of lung, trachea, liver, kidney, and muscle were low.The rat blood samples 1 h after ¹⁵NO combined blood injection were analyzed. Greater parts of the ¹⁵N in the serum were in a fraction of the ultrafiltrate and the amounts of NO₃^–in the serum were remarkably elevated compared with those of the control rats.At 24 h and 48 h after ¹⁵NO combined blood injection, the urine samples were collected. Most of the ¹⁵N in the urine was found within 24 h.Red cells from the ¹⁵NO exposed rats were washed (mixed and incubated) with the saline solution or the serum from untreated rats. The ¹⁵N in the cells was easily extracted into the solution or serum, but the ¹⁵N in the serum from the exposed animals was scarcely transferred to the red cells.Throughout the experiments, it was supposed that inhaled NO primarily reacted with hemoglobin and was changed to NO₂^–and NO₃^–. Then the metabolites were transferred to serum, part of these reacted with tissues and the others were excreted in urine in the form of NO₃^–.