1. ¹Departamento de Fisiología, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain
2. ²Departamento de Anatomía y Anatomía Patológica, Facultad de Veterinaria, Universidad Complutense de Madrid, Madrid, Spain
3. ³Departamento de Investigación, Hospital Universitario Ramón y Cajal, Madrid, Spain

Correspondence: P Recio, Departamento de Fisiología, Facultad de Farmacia, Universidad Complutense de Madrid, 28040 Madrid, Spain. E-mail: precio@farm.ucm.es

Received 15 September 2003; Revised 27 January 2004; Accepted 24 February 2004; Published online 1 April 2004.

Abstract

Our aim was to study the presence of noradrenergic nerves and to characterize the -adrenergic receptors involved in the contractions to electrical field stimulation and to -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 -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 ₁- and ₂-adrenergic antagonists (prazosin and rauwolscine, respectively). DBH-immunoreactive 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^-6 M) and tetrodotoxin (10^-6 M) and reduced by prazosin (10^-9–10^-7 M) and rauwolscine (3 10^-8–3 10^-7 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 -adrenergic agonists induce contraction of the venous rings through a heterogeneous population of ₁- and ₂-adrenoceptors.