title: Regulation of tone in pig urethral smooth muscle.
abstract: Cystometry and urethral pressure profilometry performed in Large White pigs reveal a fall in urethral pressure before micturition. The area of highest pressure in the female is in the mid-urethra. Circular smooth muscle dissected from this region generates a high spontaneous tone, which is increased by phenylephrine and carbachol, but is unaffected by guanethidine and atropine. Electrical field stimulation using different parameters produces frequency-dependent relaxations or a combination of relaxation and contraction, all sensitive to tetrodotoxin. Only the contraction is inhibited by atropine and guanethidine. However, phasic relaxations are abolished by N-nitro-L-arginine, an effect partially reversed by L- but not by D-arginine. Oxyhemoglobin also marginally reduces the relaxations. Sodium nitroprusside produces concentration-dependent relaxations of the urethral smooth muscle, maximal at 10(-5) M. It is suggested that the urethral muscle generates a high myogenic tone that maintains continence and can be enhanced by adrenergic and cholinergic input, or inhibited by NANC innervation, partially mediated by the transmitter nitric oxide.
authors.affiliation: University Department of Pharmacology, Oxford, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Bridgewater
authors.forename: H F
authors.initials: HF
authors.lastname: MacNeil
authors.forename: A F
authors.initials: AF
authors.lastname: Brading
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006145:Guanethidine / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase; D019335:Nitroarginine; D009599:Nitroprusside / Q000494:pharmacology; D010108:Oxyhemoglobins / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011312:Pressure; D013552:Swine; D014521:Urethra / Q000187:drug effects / Q000502:physiology*; D014554:Urination / Q000502:physiology; D014563:Urodynamics
chemical_list: D010108:Oxyhemoglobins; D009599:Nitroprusside; D010656:Phenylephrine; D019335:Nitroarginine; D009569:Nitric Oxide; D001285:Atropine; D002217:Carbachol; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D006145:Guanethidine