Gonadotropin-releasing hormone overcomes follicle-stimulating hormone's inhibition of insulin-like growth factor-5 synthesis and promotion of its degradation in rat granulosa cells.
The effect of a gonadotropin-releasing hormone-agonist (GnRH-a) on the synthesis of insulin-like growth factor-binding protein-5 (IGFBP-5), a physiological marker for atresia, was investigated. Granulosa cells obtained from diethylstilbestrol (DES)-treated immature female rats were cultured in serum-free medium for 72 h with GnRH-a and the conditioned media were subjected to immunoblot analysis using rat IGFBP-5 specific antibody. GnRH-a caused a dose-dependent (ED50 = 8.6 x 10(-11) M) accumulation of IGFBP-5, which migrated as 35 (non-glycosylated) and 36 kDa (glycosylated) bands under reducing conditions. A maximally effective dose of GnRH-a (10(-9) M) caused a 4-fold increase in IGFBP-5 accumulation. In contrast, increasing doses of porcine follicle-stimulating hormone (pFSH) caused a biphasic effect on IGFBP-5 accumulation. A low dose of pFSH (0.25 ng/ml) increased and higher doses of pFSH (22.5 ng/ml) decreased the 35 and 36 kDa IGFBP-5 bands. In the presence of high doses of pFSH (20.75 ng/ml), a 22 kDa band corresponding to a cleaved IGFBP-5 fragment appeared in the media. When the granulosa cells were cultured with a saturating dose of pFSH, co-addition of GnRH-a dose dependently inhibited the FSH effects (ED50 = (2.3-3.7) x 10(-10) M). The GnRH-a effects were completely blocked by co-incubation with GnRH-antagonist. IGFBP-5 mRNA accumulation levels were increased by GnRH-a in a dose dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Onoda
N
N
Department of Molecular Endocrinology, Whittier Institute for Diabetes and Endocrinology, La Jolla, CA 92093, USA.
Li
D
D
Mickey
G
G
Erickson
G
G
Shimasaki
S
S
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004054:Diethylstilbestrol / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006031:Glycosylation; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D015151:Immunoblotting; D018975:Insulin-Like Growth Factor Binding Protein 5; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D018975:Insulin-Like Growth Factor Binding Protein 5; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D004054:Diethylstilbestrol; D005640:Follicle Stimulating Hormone