Impairment of corpus cavernosal smooth muscle relaxation by glycosylated human haemoglobin

Objective To examine the effect of HbA(1c), an isoform of glycosylated haem oglobin (GHb, a product of nonenzymatic reactions between elevated blood gl ucose and haemoglobin), on nitric oxide-mediated corpus cavernosal smooth m uscle relaxation, and to categorize the mechanisms involved. Materials and methods Corpus cavernosal tissue from Wistar rats (300-350 g body weight) was prepared for the measurement of isometric tension. After e quilibration in Krebs solution gassed with 95% O-2/5% CO2 at 37 degrees C f or 90 min, optimal resting tension was applied. Tissue was precontracted wi th 1 mu mol/L noradrenaline (NAd) and either relaxed with incremental doses of acetylcholine (ACh) or sodium nitroprusside (SNP). After washout, strip s were again precontracted with NAd and then incubated with pyrogallol (100 mu mol/L), 100 mu L of haemoglobin or 100 mu L of GHb in the presence of e ither L-arginine (100 mu mol/L), indomethacin (10 mu mol/L), allopurinol (1 00 mu mol/L), deferoxamine (100 mu mol/L), catalase (600 IU/mL), or superox ide dismutase (SOD) (120 IU/ mL) before ACh- or SNP-induced relaxation resp onses were repeated. Results Haemoglobin and GHb significantly impaired the relaxation of rat co rpus cavernosum to ACh in a dose-dependent manner. L-arginine reversed the impairment caused by Hb, but not GHb. A donor of superoxide anions, pyrogal lol, mimicked this impairment to ACh when added to control strips. Catalase , deferoxamine, indomethacin and allopurinol had no significant effect on t he impaired relaxation response to ACh, whilst L-arginine partially reverse d it. SOD completely reversed the GHb-induced impaired relaxation; GHb did not alter the relaxation response to SNP. Conclusion GHb significantly impairs endothelial NO-mediated corpus caverno sal relaxation in the rat, in vitro. This effect is caused partly by the ge neration of superoxide anions and the extracellular inactivation of NO.