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

Objective Based upon morphology studies, female gender and elder age are risk factors for developing stress urinary incontinence, however, the mechanism is not entirely clear.The aim of this study was to describe the differences in urinary continence function between the female and male rats, to measure the differences in sphincter muscle between the two genders, and to investigate the myosin heavy chain isoforms (MHCIs) expression in the urethral striated sphincter of rat to discuss the mechanism which may exist. Materials and Methods Totally16female and16male adult Fisher rats at different ages were divided into8groups, group Ⅰ (6months, female), group Ⅱ (12months, female), group Ⅲ (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 and examined the muscle fiber distribution (by Masson’s Trichrome stain) as well as the expression of the corresponding MHCIs protein and messenger RNA (mRNA)(protein and mRNA expression, using Western blot or quantitative real-time polymerase chain reaction (RT-PCR)).Results The significant differences in urinary continence function were note between the female and male rats, with female rats having marked lower abdominal leak point pressure and marked faster decrease of abdominal leak point pressure in female rats with 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-Ⅱ a, MyHC-Ⅱ b and MyHC-Ⅱ x. Comparing with the male rats, the expression of fast MHC, especially MyHC-Ⅱ b and MyHC-Ⅱ x in female rats was lower than 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 than females. The higher expression of MyHC-Ⅱb and MyHC-Ⅱ x in the males urethral striated sphincter muscles might be the molecular basis responsible for the gender-related differences in continence function.