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DOLORES PRIETO Y ALBINO GARCÍA SACRISTÁN ANAL. REAL ACAD. NAC. FARM.

ED and in the action of vasoactive drugs currently used in the
therapy of ED.

REGULATION OF PENILE VASOCONSTRICTION
AND FLACCIDITY

Sympathetic nerves

Sympathetic adrenergic nerves are responsible for the detu-
mescence of the erect penis and also contribute to the maintenance
of penile flaccidity through the tonic release of noradrenaline (10).
Noradrenaline induces contraction of CC smooth muscle and arterial
vasoconstriction, which leads to the reduction of arterial inflow
and to the collapse of the lacunar spaces, respectively, allowing
decompression of subtunical venules and venous drainage of the
corpora (5, 7, 11). Neural-released noradrenaline evokes vasocons-
triction through a mixed population of postjunctional a1- and a2-
adrenoceptors in the isolated cavernous artery (12), and only through
a1-adrenoceptors in horse penile resistance arteries (13). Noradre-
naline down-regulates its own release from adrenergic nerves acting
on inhibitory prejunctional a2-adrenoceptors in intracavernous
arteries (13).

Besides the mechanical restriction of the venous outflow during
the veno-occlusive mechanism, there is evidence for an active
regulation of penile veins and adrenergic stimuli induce veno-
constriction through and heterogenous population of a1- and a2-
postjunctional adrenoceptors in both circumflex (14) and deep dorsal
veins (15). In the latter, noradrenergic nerve terminals penetrate
deep in the smooth muscle effector layer which represents a
mechanism to respond faster and more extensively to the
vasoconstrictor nerve activity.

In addition to its classical vasoconstrictor role, adrenergic
transmitters can also induce vasodilatation in penile arteries through
ß-adrenoceptors, which is related to the increased plasma adrenaline
levels during erection. By acting on ß2-adrenoceptors (7, 13),
adrenaline would further increase arterial inflow to the penis in
connection with the increased metabolism and physical activity
during sexual intercourse.

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