Central galanin stimulates pituitary prolactin secretion in rats: possible involvement of hypothalamic vasoactive intestinal polypeptide.

The effect of galanin, a newly identified neuropeptide, on pituitary prolactin (PRL) secretion was examined in the rat. Intracerebroventricular (i.c.v.) injection of all 5 doses of galanin (0.4, 1, 2, 5 and 10 micrograms/rat) raised plasma PRL levels in urethane-anesthetized rats. Galanin injection (2 micrograms/rat, i.c.v.) also increased plasma PRL levels in conscious rats. The intermediate dose of galanin (2 micrograms/rat, i.c.v.) produced a greater response in plasma PRL levels than either smaller or larger doses of galanin. Intravenous injection of galanin did not affect plasma PRL levels. Passive immunization with specific anti-vasoactive intestinal polypeptide (VIP) rabbit serum suppressed plasma PRL response to galanin (2 micrograms/rat, i.c.v.) in anesthetized rats. These findings indicate that central galanin has a stimulatory role in pituitary PRL secretion via the hypothalamus in the rat and that VIP may be involved in rat PRL release induced by galanin.