The Gender-Related Differences In Rat’s Continence Function And Its Relationship With The MyHCLs Expression In Urethral Striated Sphincter Muscle

Objective Based upon morphology studies, female gender and elder age are riskfactors for developing stress urinary incontinence, however, the mechanism is not entirelyclear.The aim of this study was to describe the differences in urinary continence functionbetween the female and male rats, to measure the differences in sphincter muscle betweenthe two genders, and to investigate the myosin heavy chain isoforms (MHCIs) expression inthe urethral striated sphincter of rat to discuss the mechanism which may exist. Materialsand Methods Totally16female and16male adult Fisher rats at different ages were dividedinto8groups，group Ⅰ (6months，female)， group Ⅱ (12months，female)，groupⅢ (24months，female), group Ⅳ (32months，female)， group Ⅴ(6months，male)，group Ⅵ(12months，male)，group Ⅶ(24months，male) and group Ⅷ(32months，male). We had tested the continence function, described the anatomy of urethra andexamined the muscle fiber distribution (by Masson’s Trichrome stain) as well as theexpression of the corresponding MHCIs protein and messenger RNA (mRNA)(protein andmRNA expression, using Western blot or quantitative real-time polymerase chain reaction(RT-PCR)).Results The significant differences in urinary continence function were notebetween the female and male rats, with female rats having marked lower abdominal leakpoint pressure and marked faster decrease of abdominal leak point pressure in female ratswith aging. Female rats were noted having less volume of striated muscle than male rats.The outcome revealed that the urethral striated muscles consist of four kind of isoforms:MyHC-Ⅰ,MyHC-Ⅱa, MyHC-Ⅱb and MyHC-Ⅱx. Comparing with the male rats, theexpression of fast MHC, especially MyHC-Ⅱb and MyHC-Ⅱx in female rats was lowerthan those in male, while the slow MHC shows opposite at the same time. Conclusions:Gender-related differences were noted in urinary continence function in rats as evaluated with urodynamic studies. The male rats demonstrated better continence function thanfemales. The higher expression of MyHC-Ⅱb and MyHC-Ⅱx in the males urethral striatedsphincter muscles might be the molecular basis responsible for the gender-relateddifferences in continence function.