The effects of short-term and long-term diabetes mellitus on urethral function were investigated to determine the contribution of urethral dysfunction to diabetes mellitus voiding dysfunction.Materials and Methods
Isovolumetric bladder pressure, urethral perfusion pressure and external urethral sphincter electromyography were measured in urethane anesthetized, female Sprague-Dawley rats (Charles River Laboratories, Wilmington, Massachusetts) 5 or 10 weeks after streptozotocin induced diabetes mellitus. Urethral responses to serial administration of the skeletal muscle blocker α-bungarotoxin, the nitric oxide synthase inhibitor Nω-nitro-L-arginine and the α-adrenergic agonist L-phenylephrine were determined in diabetes mellitus and age matched controls.Results
Peak bladder pressures and contraction amplitudes were significantly decreased in diabetes mellitus rats. Detrusor-sphincter dyssynergia occurred in approximately 30% of diabetes mellitus rats but never in controls. α-Bungarotoxin caused a greater decrease in baseline urethral perfusion pressure in diabetes mellitus rats than in controls (approximately 40% vs approximately 15%). Bladder contraction associated urethral smooth muscle relaxation amplitudes were significantly less in diabetes mellitus rats than in controls. Nω-nitro-L-arginine significantly suppressed urethral relaxation in controls but not in diabetes mellitus rats. L-phenylephrine significantly increased baseline urethral perfusion pressure in diabetes mellitus rats but not in controls. The unassociated conditions of insensitivity to N-nitro-L-arginine and hypersensitivity to L-phenylephrine were more common in 10-week diabetes mellitus rats than in control rats.Conclusions
Diabetes mellitus induced urethropathy is characterized by external urethral sphincter dysfunction, decreased urethral smooth muscle relaxation and nitric oxide responsiveness, and increased urethral smooth muscle responsiveness to α1-adrenergic agonists. These changes increase outlet resistance and, thereby, decrease voiding efficiency. This exacerbates voiding dysfunction, creating a vicious cycle of progressive lower urinary tract damage and dysfunction. Early intervention targeting outlet resistance may be indicated.