title: Carbon monoxide relaxes the female pig urethra as effectively as nitric oxide in the presence of YC-1.
abstract: OBJECTIVE
  Nitric oxide (NO) and carbon monoxide (CO) have been suggested to relax smooth muscle by activating soluble guanylate cyclase (sGC), binding to the same site of the enzyme. 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) (Cayman Co., Malmö, Sweden) increases the catalytic rate of sGC by binding to an allosteric site. We investigated whether YC-1 can modulate the relaxant responses of isolated urethral smooth muscle to exogenous CO, (NO) and electrical field stimulation.
  
  
  METHODS
  In spontaneously active and noradrenaline (Sigma-Aldrich Chemie GmbH, Steinheim, Germany) pre-contracted preparations of circular urethral smooth muscle from female pigs relaxant responses were evoked by electrical field stimulation before and after incubation with 10(-5) M. YC-1. The concentration-response curves for CO and NO were investigated in noradrenaline pre-contracted strips before and after incubation with YC-1. The tissue contents of cyclic 3',5'-guanosine monophosphate (cGMP) and cyclic adenosine monophosphate after electrical field stimulation, and the administration of CO or NO was investigated in the absence and presence of YC-1.
  
  
  RESULTS
  YC-1 significantly increased the amplitude of the relaxations evoked by electrical field stimulation, CO and NO, and simultaneously caused significant increases in the cGMP content in all preparations. The effect on CO induced relaxant responses was conspicuous. In the presence of YC-1 the potency and maximal relaxant effect of CO were similar to those of NO in the absence of YC-1.
  
  
  CONCLUSIONS
  YC-1 enhances cGMP dependent relaxant responses of the female pig urethra in vitro. The finding that the response to CO was greatly increased after sensitizing sGC suggests a potential for CO as a relaxant mediator in urethral smooth muscle.
authors.affiliation: Department of Clinical Pharmacology, Lund University Hospital, Lund, Sweden.
authors.forename: Annette
authors.initials: A
authors.lastname: Schroder
authors.forename: Petter
authors.initials: P
authors.lastname: Hedlund
authors.forename: Karl-Erik
authors.initials: KE
authors.lastname: Andersson
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology*; D004558:Electric Stimulation; D020536:Enzyme Activators / Q000494:pharmacology*; D005260:Female; D007191:Indazoles / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects* / Q000502:physiology; D009569:Nitric Oxide / Q000494:pharmacology*; D013552:Swine; D014521:Urethra / Q000502:physiology*
chemical_list: D020536:Enzyme Activators; D007191:Indazoles; C090937:3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole; D009569:Nitric Oxide; D002248:Carbon Monoxide