Effects of dopaminergic antagonist and agonist on oxytocin release induced by various stimuli.
(1) Haloperidol, a dopaminergic antagonist was injected i.p. or into the 3rd ventricle (i.c.v.) of lactating rats to determine whether or not a dopaminergic component was involved in the reflex release of oxytocin (OT) induced by (a) vaginal dilatation (Ferguson reflex), (b) vagal stimulation (vago-pituitary reflex), (c) suckling (milk-ejection reflex). Moreover, we examined the effect of a dopaminergic agonist, apomorphine, on the milk-ejection (ME) reflex. (2) I.c.v. injection of 20 microgram haloperidol inhibited the vaginal and vagal reflexes. The inhibition of the ME reflex produced by 2, 5 or 8 mg/kg i.p. or by 20 and 40 microgram i.c.v. haloperidol was dose-dependent. Apomorphine (10 mg/kg i.p.) had no effect. (3) The results suggest that a dopaminergic component must be involved in OT release whatever the peripheral stimulus.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D005260:Female; D006220:Haloperidol / Q000494:pharmacology*; D007774:Lactation / Q000187:drug effects; D010121:Oxytocin / Q000502:physiology*; D010812:Physical Stimulation; D011247:Pregnancy; D051381:Rats; D014621:Vagina / Q000187:drug effects / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology
D010121:Oxytocin; D006220:Haloperidol; D001058:Apomorphine