Prejunctional alpha 2-adrenoceptors inhibit nitrergic neurotransmission in horse penile resistance arteries

J Urol. 1997 Jun;157(6):2356-60.


Purpose: To study the influence of alpha-adrenergic stimuli on non-adrenergic non-cholinergic (NANC) neurogenic relaxation in isolated horse penile resistance arteries.

Materials and 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.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
  • Adrenergic alpha-Agonists / pharmacology
  • Animals
  • Arteries / drug effects
  • Arteries / physiology
  • Azepines / pharmacology
  • Electric Stimulation
  • Enzyme Inhibitors / pharmacology
  • Horses
  • Male
  • Muscle Relaxation / drug effects
  • Muscle, Smooth, Vascular / drug effects
  • Nitric Oxide / physiology*
  • Nitroarginine / pharmacology
  • Penis / blood supply*
  • Penis / drug effects
  • Prostaglandin Endoperoxides, Synthetic / pharmacology
  • Receptors, Adrenergic, alpha-2 / drug effects
  • Receptors, Adrenergic, alpha-2 / physiology*
  • Thromboxane A2 / analogs & derivatives
  • Thromboxane A2 / pharmacology
  • Vasoconstrictor Agents / pharmacology


  • Adrenergic alpha-Agonists
  • Azepines
  • Enzyme Inhibitors
  • Prostaglandin Endoperoxides, Synthetic
  • Receptors, Adrenergic, alpha-2
  • Vasoconstrictor Agents
  • Nitroarginine
  • Nitric Oxide
  • Thromboxane A2
  • 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
  • talipexole