Homologous upregulation of GnRH receptor mRNA by continuous GnRH in cultured rat pituitary cells.
The present study examined the effects of continuous treatment with gonadotropin-releasing hormone (GnRH) on GnRH receptor (GnRH-R) mRNA levels in dispersed cultures of rat pituitary cells. Pituitary GnRH-R mRNA levels were determined by competitive reverse transcriptase polymerase chain reaction. When pituitary cells were continuously exposed to a low dose of GnRH (0.2 nM), GnRH-R mRNA levels were transiently increased. The levels of GnRH-R mRNA were significantly increased up to 6 h and diminished to untreated levels by 24 h. Luteinizing hormone (LH) release was also increased significantly up to 12 h, maintaining similar levels in LH release thereafter. When GnRH antagonist ([D-pGlu1, D-Phe2, D-Trp3,6]-LH-RH) was added to the cultures together with GnRH (0.2 nM) for 6 h, the stimulatory effect of GnRH on GnRH-R mRNA levels and LH release was significantly diminished in a dose-related manner. In another experiment, pituitary cells were treated with various doses of GnRH (0.02-200 nM) for a relatively short (6 h) or a longer (24 h) period. When pituitary cells were exposed for 6 h, all doses of GnRH (0.02-200 nM) significantly increased GnRH-R mRNA levels in a dose-dependent manner. By contrast, continuous exposure to GnRH for 24 h was ineffective in changing pituitary GnRH-R mRNA levels at any given doses. These results indicate that the duration of GnRH treatment is critical for upregulation of GnRH-R mRNA by continuous GnRH. When pituitary cells were treated for 6 h with either a continuous mode of GnRH (0.2 nM) or an hourly pulsatile mode of GnRH (0.2 nM, 6 min/h), both treatments significantly augmented GnRH-R mRNA levels. Thus, the modes of GnRH application, if treated for a relatively short period, do not appear to make a significant difference in upregulation of GnRH-R mRNA levels. Collectively, our data provide strong evidence that continuous GnRH application is able to upregulate pituitary GnRH-R mRNA levels, if treated for a relatively short period (6 h).
Cheon
M
M
Endocrine Laboratory, Medical Research Center, College of Medicine, Yonsei University, Seoul, South Korea.
Park
D
D
Kim
K
K
Park
S D
SD
Ryu
K
K
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011966:Receptors, LHRH / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects*
D012333:RNA, Messenger; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone