Isoprostane 8-epi PGF2 alpha, a product of oxidative stress, is synthesized in the bladder and causes detrusor smooth muscle contraction

Isoprostane 8-epi PGF2 alpha is a product of oxidative stress that causes p otent smooth muscle contraction. Its production increases in conditions ass ociated with oxidative stress such as in diabetes, smoking, and aging. The aim was to study whether the urinary bladder syn thesizes isoprostane 8-epi PGF2 alpha and releases to the urine and whether isoprostane 8-epi PGF2 al pha causes bladder smooth muscle contraction. Urine samples were obtained t ransurethrally from 12 male New Zealand white rabbits for measurement of is oprostane 8-epi PGF2 alpha levels. To examine whether bladder synthesizes i soprostane S-epi PGF2 alpha, both ureters were ligated, then the bladder wa s washed 5 times by filling and emptying with normal saline. Bladder was re filled with normal saline, and at 5 minutes a bladder washout sample was ta ken. After this, the bladder was contracted by nerve stimulation periodical ly for 30 minutes, and then another washout sample was taken. Strips of bla dder tissues were processed for study of isoprostane 8-epi PGF2 alpha produ ction in tissue culture chambers and for isometric tension measurements in the organ bath. Enzyme immunoassay (EIA) revealed a remarkable amount of is oprostane 8-epi PGF2 alpha in the rabbit urine. EIA of washout samples show ed that the bladder synthesizes isoprostane 8-epi PGF2 alpha and its produc tion increases with nerve stimulation-induced contractions. EIA of samples from the tissue culture media showed that bladder strips synthesize isopros tane 8-epi PGF2 alpha in vitro. Electrical field stimulation (EFS) signific antly increased the synthesis and release of isoprostane 8-epi PGF2 alpha b y the bladder strips. In the organ bath, isoprostane 8-epi PGF2 alpha cause d concentration-dependent contraction of bladder tissue. While the threshol d contraction required smaller concentration of isoprostane 8-epi PGF2 alph a (3 nmol) than carbachol (10 nmol), the amplitude of contraction to carbac hol was greater than isoprostane 8-epi PGF2 alpha. Our studies show that th e rabbit bladder synthesizes isoprostane 8-epi PGF2 alpha and releases it t o the urine. Production of isoprostane 8-epi PGF2 alpha in the bladder incr eases with nerve stimulation-induced contraction. Exogenous isoprostane 8-e pi PGF2 alpha causes significant bladder smooth muscle contraction. Our fin dings necessitate further studies to evaluate the possible role of oxidativ e stress and increased isoprostane 8-epi PGF2 alpha production in bladder d ysfunction. (C) 2000 Wiley-Liss, Inc.