The effects of androgen milieu change on erection and central dopaminergic receptor in apomorphine-induced penile erection of the rat model

Lee, Sung Won; Paick, Jae Seung

Abstract

The systemic administration of low doses of dopamine(DA) agonist, such as apomorphine, LY 171555 and n-propyl norapomorphine induces penile erection and yawning in rats. Such a response is apparently mediated by the stimulation of central DA receptors of the D2 type and studies have suggested a localization of this action to the paraventricular nucleus(PVN) of the hypothalamus. We have investigated the effect of serum testosterone level on the apomorphine induced penile erection and yawning and the effect of serum testosterone level on the in vitro binding of [3H]N -n -propyl norapomorphine ( [3H]NPA) in cryostat from the paraventricular nucleus (PVN) of the hypothalamus in rats. All rats of control group demonstrated an erectile response and yawning behavior. Castrated rats did not have erections and had diminished yawning but responded normally after testosterone administration. In autoradiography, castration elicited significant reduction in the specific binding of 0.25 nM [ 3H] NPA to D2 receptor sites in paraventricular nucleus, but after testosterone replacement the specific binding increased above control level. Testosterone was necessary to the maintenance of a specific dopaminergic centrally mediated erection and it's blood level affects the binding properties of tritium NPA from paraventricular nucleus of hypothalamus. In these study we could suggest one aspect of androgen action on penile erection and the rationale of androgen replacement therapy.