To assess whether the secretory clearance of
N1-methylnicotinamide (NMN), an endogenous organic
cation, represents renal tubular secretion of the organic
cation, the relationship between the secretory clearance of NMN, CLscn(NMN), and that of
tetraethylammonium bromide (
TEA), CLscn(
TEA), was examined in normal and experimental
renal failure (ERF) rats.
TEA was selected as a representative organic
cation secreted by the kidney. ERF was induced by
glycerol,
folate,
salicylate,
uranium, and
gentamicin, substances which have been demonstrated to produce specific damage to the kidney by pathophysiological studies. Glomerular filtration rate (GFR), CLscn(NMN), and CLscn(
TEA) decreased significantly in most of ERF rats, while blood
urea nitrogen (BUN) increased significantly in all ERF rats. There was a statistically significant correlation (r = 0.952, p less than 0.001) between the endogenous CLscn(NMN) and CLscn(
TEA) in both the normal and ERF rats. Correlation analysis revealed that CLscn(NMN) was superior to GFR in the degree of relationship to CLscn(
TEA), but BUN could not be used as an index for the secretion of NMN or
TEA. Although the plasma concentration of NMN in most of the ERF rats was much higher than that in the normal rats, it affected neither the urinary clearance of NMN itself nor the excretion of
TEA. From these findings, we propose that CLscn(NMN) can be used as an index to assess renal tubular function for the secretion of organic
cations that are excreted by both filtration and secretion without reabsorption.