Immunohistochemical and functional evidence for a noradrenergic regulation in the horse penile deep dorsal vein

Abstract

Our aim was to study the presence of noradrenergic nerves and to characterize the a-adrenergic receptors involved in the contractions to electrical field stimulation and to a-adrenergic agonists of the horse penile deep dorsal vein. Noradrenergic fibres were visualized by immunohistochemistry using an antibody against dopamine-beta-hydroxylase (DBH). For functional studies, the responses of the venous rings to electrical field stimulation and to a-adrenergic agonists (noradrenaline, phenylephrine and BHT 920) were studied in the absence and the presence of noradrenergic transmission-and neuronal sodium channel-blockers (guanethidine and tetrodotoxin, respectively) and of a 1 -and a 2 -adrenergic antagonists (prazosin and rauwolscine, respectively). DBHimmunoreactive fibres were present in the adventitia and in the media layer of the venous rings. Electrical field stimulation (0.5-32 Hz) caused frequency-dependent contractions that were abolished by guanethidine (10 À6 M) and tetrodotoxin (10 À6 M) and reduced by prazosin (10 À9 -10 À7 M) and rauwolscine (3 Â 10 À8 -3 Â 10 À7 M). Noradrenaline, phenylephrine and BHT 920 induced equipotent contractions of the rings. Prazosin and rauwolscine competitively antagonized the contractions to phenylephrine and BHT 920, respectively. In conclusion, DBH-immunoreactive nerve fibres are present in the horse penile dorsal vein. Both transmural nerve stimulation and a-adrenergic agonists induce contraction of the venous rings through a heterogeneous population of a 1 -and a 2 -adrenoceptors.

Physiological regulation of penile arteries and veins

“…There is also evidence for an adrenergic regulation of penile veins, and adrenergic stimuli induce venoconstriction through a heterogeneous population of a 1 -and a 2 -postjunctional adrenoceptors in both circumflex 11 and deep dorsal veins. 24 In the Physiological regulation of penile arteries and veins D Prieto latter, noradrenergic nerve terminals penetrate deep in the smooth muscle effector layer which suggests a mechanism to respond faster and more extensively to the vasoconstrictor nerve activity, 24 thus reinforcing the concept of an active regulation of penile venous tone during detumescence.…”

The Adrenergic System in Vascular Smooth Muscle

“…Although corpus cavernosum may be controlled mainly by α 1 -adrenoceptors, contractions of the cavernous artery may involve both α 1 -and α 2 -adrenoceptors and α 2 -adrenoceptors may also be involved in nerve-stimulation-evoked contractions [62]. Penile veins are also reported to be constricted by α 1 -and α 2 -adrenoceptor stimulation, in both agonist-and nerve-mediated studies [113]. β 2 -Adrenoceptors have been reported to be involved in relaxation of the human corpus cavernosum [25], but in the rabbit this does not seem to involve β 1 -or β 2 -adrenoceptors, suggesting an atypical or β 3 -adrenoceptor action [132], and a β 3 -adrenoceptor-mediated relaxation has also been reported in man [23].…”