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The effects of naloxone infusion on plasma prolactin (PRL) levels and on the PRL response to mechanical breast emptying were investigated in a group of puerperal women, Five, 10, and 20 mg naloxone administered to women on days 2 to 3 of the puerperium produced no significant change in serum PRL. The same dose of naloxone had no significant effect on serum PRL response to mechanical breast stimulation in puerperal women. The results suggest that endogenous opioid peptides are not major modulators of PRL secretion in the puerperium.

The effects of a 5 day course of Piribedil, a dopaminergic agonist, on prolactin release evoked by mechanical breast emptying in puerperal women, was investigated. A daily dose of 75 mg. caused a significant decrease in the prolactin response to mechanical breast stimulation. Piribedil also proved clinically useful in inhibiting lactation. The role of dopaminergic mechanisms in the regulation of prolactin release induced by mechanical breast emptying are discussed.

Ten women were studied during the first post-partum week. Mechanical breast emptying with a breast pump for 30 min induced a marked increase in plasma prolactin (PRL) reaching a maximum 30 min after the beginning of stimulation. In all patients oral administration of the antiserotonin agent metergoline, 8 mg daily for two days, completely blocked any PRL secretion induced by breast stimulation. These results confirm the inhibitory effect of metergoline on PRL release.