Luteinizing hormone-releasing hormone (LH-RH) antagonist Cetrorelix down-regulates the mRNA expression of pituitary receptors for LH-RH by counteracting the stimulatory effect of endogenous LH-RH.
The mechanisms through which LH-RH antagonists suppress gonadotroph functions and LH-RH receptor (LH-RH-R) production are incompletely understood. To elucidate these mechanisms, we investigated the effects of Cetrorelix on the mRNA expression of pituitary LH-RH-R and luteinizing hormone (LH) secretion in three experimental systems with different pituitary LH-RH environments. Ovariectomy induced 3.61-fold and 6.34-fold increases in the mRNA expression of pituitary LH-RH-R in rats after 11 and 21 days, respectively. After (5 h) a single injection of 100 microg Cetrorelix, no significant decrease occurred in the mRNA levels of pituitary LH-RH-R in ovariectomized (OVX) rats with high pituitary exposure to LH-RH, but there was a significant 23.2% reduction in cycling rats with normal hypophysial LH-RH environment. Prolonged treatment for 10 days with a Cetrorelix depot formulation releasing 100 microg/day decreased the concentration of mRNA for pituitary LH-RH-R by 72.6% in OVX rats, but only by 32.9% in normal rats. The decline in serum LH was 98.7% in OVX rats and 63.2% in normal rats, resulting in a minimal 0.1--0.2 ng/ml LH concentration in both groups. A continuous exposure of pituitary cells to 100 nM Cetrorelix in the superfusion system, which is devoid of LH-RH, did not cause any significant changes in LH-RH-R mRNA level. These studies demonstrate that prolonged exposure to Cetrorelix in vivo, but not in vitro, down-regulates the mRNA expression of the pituitary receptors for LH-RH. Our findings indicate that LH-RH antagonists exert their inhibitory effects on the gene expression of pituitary LH-RH-R by counteracting the stimulatory effect of endogenous LH-RH.
Kovacs
M
M
Endocrine, Polypeptide, and Cancer Institute, Veterans Affairs Medical Center, New Orleans, LA 70112, USA.
Schally
A V
AV
Csernus
B
B
Rekasi
Z
Z
D000818:Animals; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism*; D006727:Hormone Antagonists / Q000008:administration & dosage / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D010052:Ovariectomy; D010902:Pituitary Gland / Q000166:cytology; D012333:RNA, Messenger; D051381:Rats; D017207:Rats, Sprague-Dawley; D011966:Receptors, LHRH / Q000235:genetics*; D013997:Time Factors
D006727:Hormone Antagonists; D012333:RNA, Messenger; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; C062876:cetrorelix