Pregnancy augments nitric oxide-dependent dilator response to acetylcholine in the human uterine artery

The influence of pregnancy on the dilator effects of acetylcholine in theisolated human uterine artery was investigated. Acetylcholine (0.1 nM to0.1 microM) produced concentration- and endothelium-dependent relaxation ofnorepinephrine (3 microM)-induced contraction. The relaxation was greaterin arteries from pregnant patients (P arteries) than from non-pregnantpatients (NP arteries). The maximal relaxation was 53.5+/-3.4% (n=21) in Parteries and 23.5+/-2.5% (n=35) in NP arteries. In both P and NP arteriesthe cholinergic relaxation was increased in the presence of superoxidedismutase and greatly reduced in the presence of the nitric oxide synthaseinhibitors, NG-mono-methyl L-arginine (L-NMMA) andL-nitro-arginine-methylester (L-NAME). The effect of these nitric oxidesynthase inhibitors was reversed by L- arginine. We conclude that pregnancyenhances acetylcholine-induced nitric oxide synthesis and release in thehuman uterine artery.