Opioid modulation of LH secretion by pig pituitary cells in vitro

Publisher Website
Google Scholar
Abstract
The effects of naloxone and .beta.-endorphin on Lh secretion by pig pituitary cells were studied in primary cultures. On Day 4 of culture, cells (105 seeded/well) were challenged with 10-9, 10-8 or 10-7 M gonadotrophin-releasing hormone (GnRH), 10-10, 10-9, 10-8 or 10-7 M-.beta.-endorphin or 10-6 M-naloxone individually or in combinations. Secreted LH was measured at 4 h and 14 h after treatment and cellular content of LH was measured after 24 h. Basal Lh secretion (Control) was 23.5 .+-. 7.6 and 36.9 .+-. 10.3 ng/well at 4 h and 24 h, respectively. Relative to control at 4 h, 10-9, 10-8 or 10-7 M-GnRH stimulated (P < 0.05) LH secretion 140%, 210% and 250%, respectively. At 24 h, LH secretion was increased (P < 0.05) by GnRH compared to control, but the dose-response to GnRH was absent. Naloxone increased (P < 0.01) LH secretion 166 .+-. 13% at 4 h and 141 .+-. 13% (P < 0.06) at 24 h. Secretion of LH after simultaneous addition of 10-8 M-GnRH plus naloxone was greater (P < 0.01) than after GnRH alone at 4 h but not at 24 h. .BETA.-Endorphin at 10-10, 10-9, 10-8 or 10-7 M failed to alter basal LH secretion at 4 h but decreased secretion at 24 h, while cellualr Lh content was similar to control at 24 h. LH secretion after simultaneous addition of 10-7 m-GnRH and 10-7 M-.beta.-endorphin was less (P < 0.01) than after GnRH at 4 h but not at 24 h, while 10-10 M-.beta.-endorphin plus 10-9 m-GnRH failed to suppress LH secretion, compared to GnRH alone. These results indicate that endogenous opioids may directly modulate LH secretion at the level of the pituitary.