On the prolactin-inhibiting effect of neurotensin. The role of dopamine.

Neurotensin (NT) when injected in a dose of 5 micrograms into the third cerebral ventricle of conscious, unrestrained male rats, outfitted with chronic third ventricle and jugular cannulae, decreased the resting prolactin (PRL) levels. NT (5 micrograms) also markedly inhibited the PRL-releasing effect of activation of central serotonin receptors by 5-hydroxytryptophan (5HTP, 15 mg/kg) in animals pretreated with fluoxetine (4 mg/kg). however, interruption of dopamine (DA) neurotransmission by either alpha-methyl-p-tyrosine (alpha MT, 250 mg/kg) or spiroperidol (0.3 mg/kg) led to a blockade of the PRL-inhibiting effect of NT. Treatment of animal with alpha MT prior to the injection of fluoxetine and 5HTP also blocked the PRL-inhibiting effect of NT. These results suggest that the central dopaminergic system mediates the PRL-inhibitory effect of NT.