The erectile response to the
short-acting dopamine (DA) receptor agonist,
apomorphine (Apo) HCl (0.25, 0.5, 0.75 and 1.0
mg sc), and placebo was evaluated in 28 impotent
patients and penile circumference monitored
using a mercury strain gauge and strip chart
A full erection (increment in penile
circumference greater than 2 cm and lasting at
least one minute) occurred in 17 patients with
Apo; no erection developed after placebo. An
erection occurred in 6/8 patients with impaired
glucose tolerance, 2/6 patients with diabetes
mellitus and in both patients on lithium.
Nine patients who responded to Apo were
treated in an open trial with bromocriptine; 6
reported improvement in potency.
Impairment in DA function may play a role in
idiopathic impotence and in impotence associated
with impaired glucose tolerance and diabetes
An erectile response to Apo may predict
therapeutic response to bromocriptine or other
long acting dopaminergic agents.
Lithium, which inhibits DA-sensitive
adenylate cyclase, does not prevent Apo-induced
erections. This provides further support
indicating that Apo induces erections by an
effect on D2 receptors.
The yawning response to placebo and
four doses of Apo HC1 (3.5, 5.0, 7.0, and 10.5
ug/kg sc) was evaluated in five normal men using
a polygraphic technique. The yawning response
was also assessed in normal young (less than 30
yrs; N = 16) and elderly (greater than 60 yrs; N
= 12) volunteers.
Under experimental conditions of study,
placebo induced spontaneous yawning. This
was antagonized by 3.5 and 5.0 ug/kg Apo HC1 but
increased by 7.0 ug/kg Apo HC1. These
observations are compatible with the view that
Apo HC1 in doses of 3.5-5.0 ug/kg stimulates
presynaptic DA receptors whereas 7.0 ug/kg
stimulates postsynaptic DA receptors.
Spontaneous and Apo-induced yawning were
significantly decreased in the elderly which
suggests that D2 receptor function declines with