title: Exogenously administered opioids contract the female rat intrinsic urethral sphincter in vivo.
abstract: OBJECTIVE
  Previous studies have reported immunoreactive opioid nerve fibers in the detrusor and lower urinary tract sphincters. However, there is a paucity of in vivo studies demonstrating the direct effect of endogenous opioids in these structures. In the present study, we investigated the contractile actions of intra-arterially administered exogenous Dynorphin-A, Met-enkephalin, Leu-enkephalin, morphine, and the opioid antagonist naltrexone on the female rat intrinsic urethral sphincter in vivo.
  
  
  METHODS
  Intraurethral pressure was recorded by a catheter placed at the maximum pressure zone of the intrinsic urethral sphincter in anesthetized female Sprague-Dawley rats. The effects of different opioids were studied and expressed as means and as percentages of pressure change (cmH(2)O) of the baseline intraurethral pressure.
  
  
  RESULTS
  Dynorphin-A, Met-enkephalin, and Leu-enkephalin evoked rapid, long-lasting contractile effects on the female rat urethra. The greatest intraurethral pressure increase was evoked by Dynorphin-A (89.2 +/- 15.3%). For Met-enkephalin, intraurethral pressure increased by 70.2 +/- 21.8% and for Leu-enkephalin, the pressure increase was 60.6 +/- 20%. Morphine, however, evoked inconsistent intraurethral pressure changes, increasing the urethral pressure in three subjects and lowering the pressure in the remaining six subjects. The opioid antagonist naltrexone reduced the intraurethral pressure by a mean of -19.0 +/- 5.8%.
  
  
  CONCLUSIONS
  Results of the present study suggest that endogenous opioids by their contractile action on the intrinsic urethral sphincter may play a role in the control of continence in rats, additional to cholinergic and noradrenergic pathways.
authors.affiliation: Department of Clinical and Experimental Physiology, Medical University of Warsaw, Warsaw, Poland. rcrayton@wum.edu.pl
authors.forename: Robert
authors.initials: R
authors.lastname: Crayton
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Soller
authors.forename: Anders
authors.initials: A
authors.lastname: Mattiasson
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Bossowska
authors.forename: Tomasz
authors.initials: T
authors.lastname: Borkowski
authors.forename: Mariusz
authors.initials: M
authors.lastname: Majewski
authors.forename: Piotr
authors.initials: P
authors.lastname: Radziszewski
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D005260:Female; D009119:Muscle Contraction / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014521:Urethra / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000701:Analgesics, Opioid