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. © 1990 S. Karger AG, Basel.