The possible effect of nitric oxide on relaxation and noradrenaline release in the isolated rabbit urethra.
We evaluated the effects of N(omega)-nitro-L-arginine (L-NNA, a nitric oxide (NO) synthase inhibitor) and carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO, a NO scavenger) on NO-mediated relaxation and noradrenaline release from adrenergic nerve endings induced by electrical field stimulation in the rabbit urethra. Electrical field stimulation caused frequency-dependent relaxation of rabbit urethral smooth muscles precontracted with phenylephrine. The relaxation responses were significantly inhibited by treatment with L-NNA or carboxy-PTIO. The inhibitory effect of carboxy-PTIO was significantly weaker than that of L-NNA. Electrical field stimulation caused significant noradrenaline release from adrenergic nerve endings in the rabbit urethra. Treatment with carboxy PTIO enhanced electrical field stimulation-induced noradrenaline release, and simultaneous application of L-NNA and carboxy-PTIO did not further enhance noradrenaline release in the rabbit urethra. As carboxy-PTIO reacts only with the free radical NO, the present results suggest that free radical NO and NO-containing compounds are involved in the L-NNA-sensitive nitrergic nerve-mediated relaxation in the rabbit urethra. At the same time free radical NO has a prejunctional action by which it may inhibit noradrenaline release from adrenergic nerves.
Yoshida
M
M
Department of Urology, Kumamoto University School of Medicine, Japan. masaki@kaiju.medic.kumamoto-u.ac.jp
Akaike
T
T
Inadome
A
A
Takahashi
W
W
Seshita
H
H
Yono
M
M
Goto
S
S
Maeda
H
H
Ueda
S
S
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009569:Nitric Oxide / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D011817:Rabbits; D014521:Urethra / Q000187:drug effects*
D009569:Nitric Oxide; D009638:Norepinephrine