Ovarian intrabursal administration of insulin-like growth factor-binding protein inhibits follicle rupture in gonadotropin-treated immature female rats.
The effects of an insulin-like growth factor-binding protein (IGF-BP) on rat follicular function were examined by using the technique of ovarian intrabursal (IB) injection. Immature female rats were injected with 15 IU of eCG followed immediately with IB injections of 4 micrograms IGF-BP3 (right ovary) and vehicle (left ovary). Forty-eight hours later, the same animals were either killed (eCG-treated group) or injected with 1 microgram of hCG as an ovulatory stimulus. These animals were killed 24 h later (eCG/hCG-treated group). Intrabursal administration of IGF-BP3 inhibited ovulations in the eCG/hCG-treated rats by 55% when compared with the contralateral vehicle-treated ovary (p = 0.01). Examination of the ovaries exposed to IGF-BP3 revealed the presence of unruptured follicles containing a matured oocyte and a disintegrated basement membrane, in addition to normal follicles and corpora lutea. In contrast, IB injection of IGF-BP3 had no effect on ovarian weights or circulating estradiol concentrations in the eCG-treated animals, and the ovaries appeared to be morphologically normal. Ligand blotting experiments using [125I]-labeled insulin-like growth factor I revealed that granulosa cells obtained from both untreated and eCG-treated rats synthesized and secreted two IGF-BPs of Mr 35,000 and 30,000. Equine chorionic gonadotropin treatment reduced the amount of the 30,000 Mr form of IGF-BP. These data suggest that locally produced ovarian IGF-BPs may modulate follicle functions in vivo.
Bicsak
T A
TA
Department of Molecular Endocrinology, Whittier Institute for Diabetes and Endocrinology, La Jolla, California 92037.
Ling
N
N
DePaolo
L V
LV
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D005260:Female; D006107:Granulosa Cells / Q000378:metabolism; D018969:Insulin-Like Growth Factor Binding Proteins; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology; D010053:Ovary / Q000033:anatomy & histology / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000378:metabolism*
D002352:Carrier Proteins; D006063:Chorionic Gonadotropin; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins