Urethral sphincter mechanism incompetence is a micturition disorder of juvenile and adult dogs. The congenital form of USMI is the second most frequent cause of urinary incontinence in juvenile animals,1,2 and approximately half of affected juvenile bitches become continent following the first or second estrus.1–3 The acquired form of USMI is the most common cause of urinary incontinence in adult spayed bitches.1,2 Urinary bladder neck position and UL may have a role in development of USMI. Pelvic bladder, defined as > 5% of the urinary bladder length located inside the pelvis,4 is a frequent radiographic finding for incontinent immature and adult bitches1,5 and is typically associated with a short urethra.6–8 A pelvic position of the bladder neck could decrease transmission of abdominal pressure to the urethra in dogs, leading to urine leakage, especially during recumbency, exercise, or barking.5,6
Development of urinary bladder function in healthy humans during neonatal to early childhood periods has been investigated.9–12 Human neonates have neuronal pathways between the bladder and cerebral cortex9,11; in human neonates, voiding of the bladder is not voluntary but involves more neural pathways than the automatic reflex to bladder distension. During the first months after birth, humans have a small bladder capacity and high bladder voiding pressure.9,10 The bladder capacity increases during the first year after birth, and the voiding pressure decreases progressively.9 Bladder capacity is stable when children are 1 to 2 years old but nearly doubles by the time children are 3 years old.10 As human infants age, the total number of bladder voiding episodes, volume of residual urine in the bladder after voiding, and number of bladder voiding episodes during the night decrease, and bladder capacity increases.9,10
Male children have sex hormone receptors in transitional epithelium of the urinary bladder neck.13 Adult women have estrogen receptors in the bladder, urethra, vagina, and pubococcygeus muscles.14,15 Sex hormone receptors are expressed in squamous epithelium of the urethra and bladder neck of women, regardless of circulating estrogen concentrations.16 However, expression of progesterone receptors in subepithelial tissues of the lower urinary tracts of women is dependent on circulating concentrations of estrogen.16 Female dogs have estrogen receptors in the proximal urethra but do not have such receptors in the kidneys, ureters, bladder, or distal urethra.17
Results of other studies regarding the effects of variations in sex hormone concentrations during the menstrual cycle on the urinary tracts of women are controversial. One group of investigators18 found that FPL of the urethra increases during the middle of the menstrual cycle in women, whereas other investigators19–22 identified no significant changes in urodynamic variables during the menstrual cycle. Another group of investigators23 found that bladder tone increases during the follicular phase of the menstrual cycle in women and that bladder tone is decreased during the luteal phase. Other investigators24 determined that the lower urogenital tract in adult female Beagles is affected by variations in circulating concentrations of hormones during the estrous cycle. Urethral resistance decreased during estrus and early diestrus in the Beagles in that study,24 whereas bladder tone increased and values of urinary tract morphometric variables changed during anestrus and proestrus. However, other investigators25 found that urethral resistance significantly decreases in female dogs after ovariectomy; that finding is not consistent with urodynamic changes that develop in sexually intact female Beagles during anestrus.24
Functional and morphometric characteristics of urinary tracts in continent and incontinent adult female dogs have been determined. However, to our knowledge, urodynamic and morphometric characteristics of lower urogenital tracts in sexually immature female dogs have not been investigated. Therefore, the purposes of the study reported here were to compare values of lower urogenital tract urodynamic and morphometric variables determined during the prepubertal (sexually immature) period and first and second estrous cycles and to determine functional and anatomic changes that develop in the lower urogenital tract during those times in healthy female Beagle littermates.
Functional profile length
Maximum urethral closure pressure
Maximum urethral pressure
Urethral sphincter mechanism incompetence
Total vaginal length
CombiScreen VET 11 PLUS, Analyticon Biotechnologies AG, Lichtenfels, Germany.
Propovet, ECUPHAR, Oostkamp, Belgium.
Libra+ Medical Measurement System, Benetec, Retie, Belgium.
Vetergesic, ECUPHAR, Oostkamp, Belgium.
ARCHITECT progesterone assay, Abbott, Lisnamuck, Longford, Ireland.
SAS/STAT software, version 9.1, SAS Institute Inc, Cary, NC.
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