Effects of Dopaminergic Antagonist and Agonist on Oxytocin Release Induced by Various Stimuli

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Abstract
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. I.c.v. injection of 20 μg 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 μg i.c.v. haloperidol was dose-dependent. Apomorphine (10 mg/kg i.p.) had no effect. The results suggest that a dopaminergic component must be involved in OT release whatever the peripheral stimulus.