Galanin-like immunoreactivity is influenced by estrogen in peripubertal and adult rats

Galanin gene expression in the anterior pituitary is potently stimulated by estrogen in adult rats. To evaluate the influence of estrogen on galanin during the peripubertal period 30- to 32-day-old female rats were treated with pregnant mare serum gonadotropin (PMSG, 10 IU s.c, 10.00 h). Galanin-like immunoreactivity (galanin-LI) in hypothalamic and pituitary tissues was evaluated 1, 2 or 3 days after PMSG treatment between 17.00 and 19.00 h. The PMSG treatment stimulated 17β-estra-diol secretion, which induced a midaftemoon LH surge 2 days after the PMSG treatment. Concentrations of galanin-LI at the time of this LH surge were elevated 82% in the anterior pituitary and 58% in the hypothalamus (without the median eminence) when compared to saline-treated female rats. On the 3rd day after the PMSG injection, galanin-LI was increased 236% in the anterior pituitary, 88% in the neurointermediate lobe and 39% in the median eminence compared to saline-treated female rats. These changes in galanin-LI were not observed in similarly aged male rats or ovariectomized rats treated with PMSG. In adult male rats, daily injections with 17β-estradiol valerate (10 µg/daily s.c.) for 1 week increased galanin-LI in the median eminence and neurointermediate lobe to an extent similar to that seen in juvenile female rats following PMSG treatment. In contrast, the high serum levels of 17β-estradiol achieved after 17β-estradiol valerate treatment increased galanin-LI in the anterior pituitary 65-fold. These studies indicate that galanin-LI is influenced by estrogen in peripubertal and adult rats. The more robust capacity of anterior pituitary galanin-LI to respond to estrogen treatment suggests differences between galanin production in anterior pituitary versus neural tissues. These studies suggest that sex differences in galanin-LI in the anterior pituitary, neurointermediate lobe and median eminence are a result of increased estrogens which are produced during sexual maturation in the female rat.