Inhibition of NMDAR reduces bladder hypertrophy and improves bladder function in cyclophosphamide induced cystitis

Abstract

Purpose: We examined the role of NMDAR in the regulation of bladder hypertrophy and function in a rat model of cyclophosphamide induced cystitis.

Materials and methods: Cystitis was induced by intraperitoneal injection of cyclophosphamide (150 mg/kg body weight). NMDAR phosphorylation (activity) and signal transduction pathways were examined by direct measurement and by specific inhibitors in vivo. Bladder hypertrophy was measured by bladder weight/body weight and type I collagen expression. Bladder function was examined by metabolic recording, conscious cystometry and detrusor muscle strip contractility in response to carbachol.

Results: NMDAR activity measured by the phosphorylation level of the NMDAR1 (NR1) subunit was expressed in the spinal cord but not in the bladder at 48 hours of cystitis. NMDAR inhibition with dizocilpine (MK-801) reduced the cystitis induced increment of bladder weight and type I collagen up-regulation in the bladder. NMDAR regulated type I collagen up-regulation was mediated by the PI3K/Akt pathway. NMDAR inhibition also attenuated cystitis induced urinary frequency measured by metabolic cage and cystometry. Cystitis decreased the responsiveness of detrusor muscle strips to carbachol, which was reversed by MK-801 in vivo. Unlike MK-801 the NMDAR antagonist D-AP5, which could not block central NMDAR activity, had no effect on bladder hypertrophy, type I collagen up-regulation or Akt activation caused by cystitis in the bladder.

Conclusions: Findings suggest that NMDAR activity has a role in cystitis induced bladder hypertrophy and overactivity. NMDAR mediated Akt activation may underlie the mechanism of bladder dysfunction.

Keywords: N-methyl-D-aspartate; collagen; cystitis; hypertrophy; interstitial; overactive; receptors; urinary bladder.