Prediction of the renal clearance of cimetidine using endogenous N-1-methylnicotinamide

We investigated the influence of the type rather than the degree of renal insufficiency on the renal clearance of drugs. Different models of site specific experimental renal failure (ERF) have been developed in the rat; proximal tubular necrosis, induced by cisplatin; papillary necrosis, induced by 2-bromoethylamine, and glomerulonephritis, induced by sodium aurothiomalate or by antiglomerular basement membrane antibody. Several parameters of kidney function were assessed: the clearance of inulin, PAH, and endogenous N-1-methylnicotinamide (NMN). Plasma BUN and creatinine concentrations, and the presence of proteinuria and glucosuria were also measured. Our results showed a nonparallel decrease in glomerular filtration rate (GFR) and tubular secretion as measured by the secretory clearance of endogenous NMN or by the secretory clearance of p-aminohippuric acid (PAH), that is incompatible with the "intact nephron hypothesis." As a result, the renal clearance of cimetidine, a drug eliminated mainly by renal secretion, correlated better with the renal clearance of endogenous NMN than with the GFR. We conclude that (i) our models of ERF demonstrated the existence of glomerulo-tubular imbalance that is contrary to expectations based on the intact nephron hypothesis; (ii) the type of the renal disease has a direct influence on the renal clearance of cimetidine; (iii) the clearance of endogenous NMN may be a valuable noninvasive test for assessing renal tubular secretion which could be useful in predicting the clearance of drugs eliminated predominantly by tubular secretion.