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 NO ⁻₃ 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 NO ⁻₂ and NO ⁻₃ . Then the metabolites were transferred to serum, part of these reacted with tissues and the others were excreted in urine in the form of NO ⁻₃ .