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Roles of attenuated neuronal nitric‐oxide synthase protein expression and accelerated arginase activity in impairing neurogenic relaxation of corpus cavernosum in aged rabbits
Author(s) -
Numao Noboru,
Masuda Hitoshi,
Sakai Yasuyuki,
Okada Youhei,
Kihara Kazunori,
Azuma Hiroshi
Publication year - 2007
Publication title -
bju international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.773
H-Index - 148
eISSN - 1464-410X
pISSN - 1464-4096
DOI - 10.1111/j.1464-410x.2007.06860.x
Subject(s) - arginase , nitric oxide , endocrinology , medicine , nitric oxide synthase , western blot , arginine , blot , chemistry , biology , biochemistry , amino acid , gene
OBJECTIVE To investigate whether changes in neuronal nitric oxide synthase (nNOS) protein expression and arginase activity are implicated in impairing the neurogenic cavernosal relaxation in aged rabbits, as NO is important in the neurogenic relaxation of corpus cavernosum during the erectile state. MATERIALS AND METHODS Cavernosal specimens of young adult (3–6 months old) and aged (36–48 months old) rabbits were used for isometric tension experiments, Western blot analysis, cGMP determination and measurements of NOS and arginase activities. RESULTS The neurogenic relaxation and cGMP production in response to electrical‐field stimulation were significantly impaired in aged cavernosal specimens. Western blot analysis showed that nNOS protein was highly expressed in cavernosal specimens from young rabbits, but was undetectable or greatly decreased in old rabbits, with no change in overall NOS activity. Arginase activity in aged cavernosal specimens was significantly higher than in young rabbits. Supplementing with excess l ‐arginine, or giving S‐ (2‐boronoethyl)‐ l ‐cysteine as an arginase inhibitor, significantly increased the neurogenic relaxation at lower frequencies only in the younger rabbits. CONCLUSION These results suggest that impairment of neurogenic and NO‐mediated relaxation in the aged corpus cavernosum possibly results from the down‐regulation of nNOS protein. The reduced l ‐arginine bioavailability to nNOS due to accelerated arginase activity would lead to further impairment of neurogenic NO production, in concert with decreased nNOS protein expression.