Young and Old Sickle Cell Disease Transgenic Mice Present Underactive Bladder

Urinary bladder dysfunction is rarely spontaneously reported by sickle cell disease (SCD) patients to their caregivers. With increasing survival of these patients, physicians may expect that urinary complaints increase in association with classical urological disorders associated with advanced age. Nocturia has long been attributed to constant increased urinary volumes in SCD. As part of the renal complications of sickling, renal medullary infarcts lead to decreased ability to concentrate urine, yielding higher daily urinary volumes, compensatory polydipsia and, eventually, the need for nocturnal bladder voiding. For comparison, the effects of alterations on bladder function have been better characterized in diabetic bladder dysfunction (DBD). It has been suggested that DBD comprehends so-called “early” and “late” phases of the disease. In the early phase of DBD, the bladder is hyperactive, leading to nocturia and urge incontinence. Later in the course of the disease, the detrusor smooth muscle becomes atonic, leading to an underactive bladder. Moreover, Berkeley sickle cell disease (SS) transgenic mice display several clinical manifestations similar to those seen in humans. Thus, the aim of this study was to evaluate the contractile mechanisms of isolated DSM (in vitro) and urinary function by cystometry (in vivo) in young (early) and old (late) SS mice. Young (3 month) old (1 year and 3 month) SS mice and young (3 month) C57BL/6 mice (control) tissues were removed and placed in Krebs solution. The strips were mounted in isolated organ baths. Cumulative concentration-response curves to muscarinic agonist, carbachol (CCh; 0.01-100 μM), hyperpolarizing solution, chloride potassium (KCl; 1-300mM) and frequency-response curves for electrical field stimulation (EFS; 1-32Hz) were obtained in DSM. Cystometry was used to evaluate the urinary function in vivo. The cumulative addition of the CCh (10nM-100µM) produced concentration dependent contractions in strips of isolated DSM. The maximal contractions induced by CCh were markedly lower in bladder muscle from the young-SS mice (0.58 ± 0.11 mN/mg of tissue; n=7; P<0.05) and old-SS mice (0.37 ± 0.11 mN/mg of tissue; n=7; P<0.05) when compared with the control mice (1.44 ± 0.23 mN/mg of tissue; n=5). No differences in the potency (pEC₅₀) values for CCh were found between control (5.92 ± 0.05; n=5), young-SS (5.80 ± 0.06; n=7) and old-SS (5.69 ± 0.10; n=7) mice. Similarly, the cumulative addition of chloride potassium (KCl: 1–300 mM) produced concentration-dependent contractions in strips of isolated DSM. The maximal contractions induced by KCl in the DSM were significantly reduced in the young-SS mice (0.74 ± 0.12 mN/mg of tissue; n=7; P<0.05) and old-SS mice (0.50 ± 0.07 mN/mg of tissue; n=7; P<0.05), when compared to the control mice (1.11 ± 0.21 mN/mg of tissue; n=5). No differences in the potency (pEC₅₀) values for KCl were found between control (1.29 ± 0.10; n=5), young-SS (1.20 ± 0.15; n=4) and old-SS (1.13 ± 0.27; n=7) mice. EFS-induced contractions in DSM of young-SS and old-SS mice were significantly decreased in the higher frequencies (8, 16 and 32 Hz), compared to control mice. In the cystometric study, control mice showed regular micturition cycles with rare non-voiding contractions. Interestingly, young- and old-SS mice showed atypical void patterns, characterized by the incapacity to produce characteristic bladder contractions to empty bladder. This result is in accordance with the data obtained in the functional in vitro study and is the first to show the underactive bladder in SCD mice. Our data demonstrate that DSM from young and old SS mice exhibit impaired contractile responses to the muscarinic agonist, KCl, and EFS indicating that SS mice (young or old) have an atonic detrusor smooth muscle, resulting in underactive bladder.

Financial Support: FAPESP/CNPq/INCTS