title: 5-HT 2A receptor activation of the external urethral sphincter and 5-HT 2C receptor inhibition of micturition: a study based on pharmacokinetics in the anaesthetized female rat.
abstract: Central and peripheral 5-hydroxytryptamine (5-HT) receptors play a critical role in the regulation of micturition. Bolus doses of 5-HT(2A/2C) receptor agonists have been shown to activate the external urethral sphincter (EUS) and to inhibit micturition. This study was designed to determine the contribution of these two 5-HT receptor subtypes to activation of the EUS and inhibition of micturition utilising pharmacokinetic knowledge to better control drug exposure. Recordings of urethral and bladder pressure, EUS-Electromyogram (EMG), the micturition reflex induced by bladder filling, blood pressure and heart rate were made in anaesthetized female rats. The effects of intravenous (i.v.) infusions of the 5-HT(2) receptor agonist (2S)-1-(6-chloro-5-fluoroindol-1-yl)propan-2-amine fumarate (Ro 60-0175) in the absence or presence of the selective 5-HT(2C) receptor antagonist 6-chloro-5-methyl-N-[6-(2-methylpyridin-3-yl)oxypyridin-3-yl]-2,3-dihydroindole-1-carboxamide dihydrochloride (SB 242084) or 5-HT(2A) receptor antagonist (R)-(2,3-dimethoxyphenyl)-[1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl]methanol (MDL-100,907) were studied on these variables. Continuous infusion of increasing concentrations of Ro 60-0175 only evoked EUS-EMG activity at the highest concentration, which was blocked by co-infusion of MDL-100,907 but not SB 242084. Urethral pressure was unaffected by any drug infusion. Ro 60-0175 at the lowest concentration inhibited the micturition reflex but as the concentration increased this was reversed to facilitation. SB 242084 blocked the inhibition while MDL-100,907 blocked the excitation. Activation of 5-HT(2A) not 5-HT(2C) receptors evoked EUS-EMG activity. In conclusion, 5-HT(2A) receptor activation facilitated the micturition reflex and evoked EUS-EMG while 5-HT(2C) receptor activation only inhibited the micturition reflex.
authors.affiliation: Department of Pharmacology, University College London, Hampstead Campus, Rowland Hill Street, London NW3 2PF, UK. yvonne.mbaki@nottingham.edu.my
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Mbaki
authors.forename: Jennifer
authors.initials: J
authors.lastname: Gardiner
authors.forename: Gordon
authors.initials: G
authors.lastname: McMurray
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Ramage
mesh_terms: D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004347:Drug Interactions; D004576:Electromyography; D005260:Female; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism*; D044405:Receptor, Serotonin, 5-HT2C / Q000378:metabolism*; D058830:Serotonin 5-HT2 Receptor Antagonists / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology; D014521:Urethra / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014554:Urination / Q000187:drug effects*
chemical_list: D044402:Receptor, Serotonin, 5-HT2A; D044405:Receptor, Serotonin, 5-HT2C; D058830:Serotonin 5-HT2 Receptor Antagonists