Effects of Age and Multiple Vaginal Births on Lower Urinary Tract Structure and Function in Nonhuman Primates

Purpose: The relative roles of urinary sphincter damage, aging, and childbirth in stress urinary incontinence (SUI), have not been established. This study was performed to elucidate the roles of these factors.Methods: The study included: (1) 8 female cynomolgus monkeys (17–19 years of age and 7–8 vaginal births each); (2) six 5-yearold nulliparous monkeys with surgically created chronic urinary sphincter dysfunction; and (3) six 5-year-old, nulliparous, nosurgery controls. Sedated abdominal leak point pressure (ALPP) and maximum urethral sphincter pressures (MUP) were measured. Sphincters, bladders, and pelvic support muscles were quantified for collagen content. Additionally, bladders were analyzed for collagen fiber thickness, length, and angle using CT-FIRE analysis of Picrosirius red-stained tissues.Results: Resting MUP values were similar in the controls and older multiparous monkeys (P>0.05). However, aging and multiple births reduced pudendal nerve-stimulated increases in MUP (P<0.05 vs. controls). ALPP values were lower in the older multiparous versus younger groups of monkeys (P<0.05). Sphincter collagen content was greater, and muscle content less, in the injury model (P<0.05 vs. controls). However, these measures were not affected by age and childbirth (P>0.05 vs. young groups). Bladder collagen content was greater, and muscle content less, in the old multiparous monkeys (P<0.05 vs. younger groups). Additionally, collagen fibers were thicker and more angular in the bladders of the older multiparous monkeys than in the other nonhuman primate groups (P<0.05). Pelvic support muscles had higher collagen and lower muscle content in the older multiparous monkeys than in the younger groups of monkeys (P<0.05).Conclusions: SUI, associated with aging and multiple childbirths, appeared to be more strongly associated with bladder dysfunction, reduced pelvic muscle support, and the compensatory response to neural stimulation than with selective urinary sphincter dysfunction.