Up-regulation of nicotinic and muscarinic receptor mRNA in rat bladder by repeated administration of nicotine in relation to the pharmacokinetics

AimsThe current study aimed to investigate the effects of repeated treatment with nicotine on nicotinic and muscarinic receptors in the rat bladder.Main methodsRats were administered nicotine (4.3 μmol/kg) subcutaneously (sc) twice a day for 10 days. The messenger RNA (mRNA) expression of nicotinic and muscarinic receptors in the bladder was examined by reverse transcription polymerase chain reaction (RT-PCR) and by a radioligand binding assay using [N-methyl-3H]scopolamine methyl chloride ([3H]NMS). The concentrations of nicotine and cotinine in plasma, tissues, and urine were estimated by ultra-performance liquid chromatography/electrospray ionization-mass spectrometry (UPLC/ESI-MS).Key findingsmRNA of nicotinic receptor subunits (α1–α7, β1–β4, ε) and muscarinic receptor subtypes (M1–M5) was detected in the rat bladder. There was a significant increase in the mRNA expression of α3, β1, β2 and β4 in the nicotine-treated rats (4.3 μmol/kg, s.c., b.i.d.) compared to the saline-treated group. Repeated administration of nicotine significantly increased the mRNA expression of the M2 and M3 muscarinic receptor subtypes in the rat bladder with a significant enhancement of [3H]NMS binding sites, compared to the saline-treated tissue. Nicotine was distributed at higher concentrations in the bladder than the heart and cerebral cortex. Furthermore, nicotine was excreted in rat urine at high concentrations.SignificanceThe present study is the first to show that repeated treatment with nicotine affects pharmacologically-relevant nicotinic and muscarinic receptors in the bladder. Such changes may contribute to the etiology of lower urinary tract symptoms (LUTS) due to cigarette smoking.