Bromocriptine inhibits galanin gene expression in the rat pituitary gland

The chronic effects of diethylstilbestrol (DES) and bromocriptine on the expression of galanin in the rat anterior pituitary were examined and compared with the expression of prolactin and vasoactive intestinal peptide (VIP) after the same type of hormonal manipulation. Total pituitary RNA was subjected to Northern blot analysis 2, 7, and 28 days after rats were implanted sc with a 10-mg DES pellet with or without concurrent treatment with bromocriptine (5 mg/kg per day). Estrogen treatment resulted in a rise in galanin, prolactin, and VIP messenger RNA (mRNA) that was particularly evident for galanin. Coadministration of bromocriptine with DES suppressed the response to estrogen with galanin, prolactin, and VIP mRNA levels being in general lower than when treatment with estrogen alone was used. In the combined treatment group there was an increase in the levels for the three mRNA species over the control group. Pituitary content of galanin and prolactin measured by radioimmunoassay exhibited a temporal pattern similar to that of corresponding mRNA levels after administration of estrogen alone or in combination with bromocriptine. The rise in galanin content (up to 78-fold) was higher than the increase in prolactin immunoreactivity (up to 6.5-fold compared to control). Bromocriptine partially suppressed the estrogen-induced increase in the content of these peptides. The changes in galanin and prolactin peptide levels in the plasma paralleled those found in the pituitary. This study demonstrates that the neuropeptides galanin and VIP are coregulated with prolactin after estrogen and bromocriptine administration. Since galanin and VIP are known to stimulate prolactin secretion it is possible that they mediate, at least in part, the effects of estrogen and bromocriptine on pituitary size and/or prolactin release.