026 Testosterone deficiency causes endothelial dysfunction via elevation of asymmetric dimethylarginine (ADMA) and oxidative stress in castrated rats

Abstract

Testosterone is thought to mediate the erectile function by producing an adequate nitric oxide (NO), and therefore testosterone deficiency results in erectile dysfunction via reduced NO bioavailability. However, the mechanisms underlying endothelial dysfunction in testosterone deficiency remain unclear. We investigated the mechanism of endothelial dysfunction in castrated rats by focusing on the relationship between testosterone deficiency and asymmetric dimethylarginine (ADMA), an endogenous NO synthase (NOS) inhibitor. Male rats were categorised into the following groups: castrated (Cast), castrated with testosterone (3 mg/kg/day) (Cast+T), and sham (Sham). Erectile function using ICP measurements, endothelial function using isometric tension, ADMA levels using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) and oxidative stress (NADPH oxidase and p22phox), and inflammatory biomarker expression (IL-6, NF-κB) and ADMA generated (DDAH) were assessed 4 weeks postoperatively. Oxidative stress analysis was also performed by quantifying the 8-OHdG levels of DNA. The ICP/MAP ratios were 0.61 ± 0.03 in Sham, 0.26 ± 0.04 in Cast (p < 0.01 vs. Sham), and 0.56 ± 0.06 in Cast+T (p < 0.01 vs. Cast). Relaxation responses induced by acetylcholine were decreased in Cast compared to Sham and Cast+T (p < 0.05). Cast rats also had significantly lower serum NO metabolite (NOx) levels than Sham counterparts (Sham, 4.20 ± 0.54 μmol/L; Cast, 2.87 ± 0.28 μmol/L; p < 0.01). However, the Cast+T and Sham rats had similar serum NOx levels (Cast+T, 4.39 ± 0.77 μmol/L; p > 0.05). Serum ADMA levels were significantly higher in Cast (297.3 ± 22.9 ng/mL) than in Sham (200.8 ± 9.4 ng/mL) or Cast+T (198.1 ± 27.7 ng/mL; both p < 0.05). Oxidative stress and inflammatory marker messenger RNA expression were significantly higher in Cast than in Sham and Cast+T (p < 0.05). Expression of the ADMA generated biomarker was significantly higher in Cast than in Sham or Cast+T (both, p < 0.01). The 8-OHdG levels were significantly higher in Cast (18.7 ± 0.9 ng/DNA 1 ng) than in Sham (13.9 ± 1.4 ng/DNA 1 ng) or Cast+T (13.3 ± 1.7 ng/DNA; both p < 0.05).