Prejunctional alpha 2-adrenoceptors inhibit nitrergic neurotransmission in horse penile resistance arteries.
OBJECTIVE
To study the influence of alpha-adrenergic stimuli on non-adrenergic non-cholinergic (NANC) neurogenic relaxation in isolated horse penile resistance arteries.


METHODS
Deep intracavernous penile arteries with an internal lumen diameter of 200-500 microns., isolated from the corpus cavernosum of young horses, were mounted in microvascular myographs for isometric tension recording and electrical field stimulation (EFS) of autonomic nerve terminals.


RESULTS
In the presence of guanethidine (10(-5) M) and atropine (10(-7) M) tone of the arteries was raised by the thromboxane analogue, U46619. EFS (1, 4 and 32 Hz) induced frequency-dependent relaxations, which were abolished in the presence of tetrodotoxin, while NG-nitro-L-arginine (L-NOARG, 10(-4) M) abolished the relaxations to EFS at 1 Hz, and significantly reduced the relaxations at 4 Hz and 32 Hz by 82.5 +/- 10.2% and 52.9 +/- 4.7%, respectively (n = 6). EFS induced relaxations of a similar magnitude in penile arteries contracted with U46619 or the alpha 1-adrenoceptor agonist, phenylephrine, while the alpha 2-adrenoceptor agonist, BHT920 (10(-6) M), produced an inhibitory effect on the EFS-evoked relaxations which was inversely related to the stimulus frequency (1, 4 and 32 Hz). BHT920 had no effect on the relaxations induced by exogenous nitric oxide (NO), added as acidified sodium nitrite (10(-6)-10(-3) M). The inhibitory effect of BHT920 on NANC relaxations was reversed by 10(-7) M rauwolscine.


CONCLUSIONS
These results suggest that the release of a NANC neurotransmitter primarily thought to be NO is inhibited by stimulation of prejunctional alpha 2-adrenoceptors in horse penile resistance arteries.
Simonsen
U
U
Departamento de Fisiología, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
Prieto
D
D
Hernández
M
M
Sáenz de Tejada
I
I
García-Sacristán
A
A
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D001381:Azepines / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006736:Horses; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D010413:Penis / Q000098:blood supply* / Q000187:drug effects; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D004791:Enzyme Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D019335:Nitroarginine; D009569:Nitric Oxide; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C024763:talipexole