Relaxation of sheep urethral muscle induced by electrical stimulation of nerves: involvement of nitric oxide.
Isolated smooth muscle preparations from the sheep urethra responded to electrical field stimulation with contraction when basal tension was low (5-6 mN), but with relaxation when the preparations were contracted with noradrenaline (NA), clonidine, or prostaglandin F2a. No relaxant response could be elicited in high K+ (124 mM) contracted preparations. Electrically induced relaxations had a threshold of less than 1 Hz and a maximum at 8 Hz. Both contractant and relaxant responses were abolished by tetrodotoxin, indicating that they were caused by transmitters released from nerves. The amplitude of the relaxant responses showed a highly significant correlation to the tension induced by noradrenaline. A coefficient (R/T) was calculated relating relaxation to noradrenaline-induced tension. In this way it is possible to separate the effect of drugs on muscle tension (non-specific effect) from their action on the electrically induced relaxation (specific effect). Chemical sympathectomy with 6-OHDA did not significantly modify the relaxant response to 6 Hz in noradrenaline contracted strips, as evaluated by the R/T coefficient. The electrically induced relaxation was not affected by hexamethonium, propranolol, phentolamine, muscarinic receptor blockade, cocaine, indomethacin, or methysergide. Both nifedipine and Bay K 8644 inhibited significantly the response induced by electrical stimulation, decreasing its maximum. Nifedipine, but not Bay K 8644, significantly reduced the level of tension induced by noradrenaline, and its effect, evaluated by the R/T coefficient, was an increase in the electrically induced relaxation, whereas Bay K 8644 had a significant inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Garcia-Pascual
A
A
Department of Physiology, Faculty of Veterinary, Complutense University, Madrid, Spain.
Costa
G
G
Garcia-Sacristan
A
A
Andersson
K E
KE
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001341:Autonomic Nervous System / Q000502:physiology; D004558:Electric Stimulation; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism*; D019335:Nitroarginine; D016627:Oxidopamine; D012756:Sheep / Q000502:physiology; D013563:Sympathectomy, Chemical; D014521:Urethra / Q000187:drug effects / Q000502:physiology*
D006892:Hydroxydopamines; D019335:Nitroarginine; D009569:Nitric Oxide; D016627:Oxidopamine; D001120:Arginine