Nitrergic relaxation of the horse corpus cavernosum. Role of cGMP.
The involvement of nitric oxide (NO) and the mechanisms mediating neurogenic relaxation were investigated in the horse corpus cavernosum. NADPH-diaphorase activity was expressed in nerve fibres around arteries and muscular bundles in the horse trabecular tissue. Relaxations in response to electrical field stimulation were tetrodotoxin (10(-6) M)-sensitive, indicating their neurogenic origin. The NO synthase inhibitor, L-NO-arginine (L-NO-Arg, 3 x 10(-5) M), abolished the electrically induced relaxations, which were significantly reversed by L-arginine (3 x 10(-3) M). Exogenous NO (10(-6)-10(-3) M) evoked relaxations which were unaffected by L-NO-Arg. 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 5 x 10(-6) M), an inhibitor of guanylate cyclase activation by NO, reduced the relaxations in response to electrical stimulation and exogenous NO. Iberiotoxin (3 x 10(-8) M) or apamin (5 x 10(-7) M), inhibitors of large and small conductance Ca2+-activated K+ channels, respectively, and glibenclamide (3 x 10(-6) M), a blocker of ATP-sensitive K+ channels, failed to modify the relaxations with NO. It is suggested that NO is present in nerve fibres of the horse corpus cavernosum and relaxes smooth muscle through a guanylate cyclase-dependent mechanism. Neither Ca2+-activated nor ATP-sensitive K+ channels seem to be involved in these relaxations.
Recio
P
P
Departamento de Fisiología, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
López
P G
PG
Hernández
M
M
Prieto
D
D
Contreras
J
J
García-Sacristán
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006152:Cyclic GMP / Q000037:antagonists & inhibitors*; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006736:Horses; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009412:Nerve Fibers / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D010413:Penis / Q000187:drug effects* / Q000294:innervation; D015221:Potassium Channels / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D004791:Enzyme Inhibitors; D010069:Oxadiazoles; D015221:Potassium Channels; D011810:Quinoxalines; D019335:Nitroarginine; D013779:Tetrodotoxin; D000255:Adenosine Triphosphate; D019001:Nitric Oxide Synthase; D009252:NADPH Dehydrogenase; D006152:Cyclic GMP; D002118:Calcium