Comparison of Oxybutynin and its Active Metabolite, N-Desethyl-Oxybutynin, in the Human Detrusor and Parotid Gland

ABSTRACTPurpose: To compare in vitro the antimuscarinic effect of oxybutynin and its active metabolite, N-desethyl-oxybutynin, on human detrusor, and their binding characteristics in detrusor and parotid gland.Materials and Methods: Antimuscarinic effect in the detrusor was assessed as the ability of the drugs to inhibit carbachol-induced contractions and contractions induced by electrical nerve stimulation. In addition, the drugs' ability to displace3 H-QNB from muscarinic receptors was investigated.Results: Both oxybutynin and N-desethyl-oxybutynin caused a rightward shift of the concentration-response curve for carbachol without depression of the maximum, indicating a competitive antagonism. The pA2 values were 7.8 for oxybutynin and 7.6 for N-desethyl-oxybutynin. Contractions induced by electrical nerve stimulation were depressed by 87% by oxybutynin (10 micro M) and by 91% by N-desethyl-oxybutynin (10 micro M). In radioligand receptor binding studies on the detrusor, oxybutynin and N-desethyl-oxybuty...