Steroidogenic responses of pig corpora lutea to insulin-like growth factor I (IGF-I) throughout the oestrous cycle.
This study was designed to investigate the roles of insulin-like growth factor I (IGF-I), IGF-type I receptor (IGF-IR) and IGF-binding proteins (IGFBPs) in regulating progesterone secretion by pig corpora lutea during the oestrous cycle, and the signal transduction pathways involved in mediating the steroidogenic actions of IGF-I. Corpora lutea were collected on days 4, 7, 10, 13 and 15 or 16 of the oestrous cycle, enzyme dissociated and the luteal cells were cultured for 24 h in Medium 199 with IGF-I (0-100 ng ml(-1)), long R(3)-IGF-I (0-100 ng ml(-1)), anti-IGF-I (Sm 1.2B; 0-10 microg ml(-1)), anti-IGF-IR (alphaIR3; 0-2 microg ml(-1)), or IGF-I signal transduction pathway inhibitors (phosphatidylinositol (PI)-3-kinase: 100 nmol Wortmannin l(-1) and 10 micromol LY 294002 l(-1); MAP kinase: 50 micromol PD 98059 l(-1)) to investigate their effects on IGF-I (100 ng ml(-1)) stimulated progesterone secretion. Pig luteal cells displayed dose-dependent responses to IGF-I and long R(3)-IGF-I on days 4 and 7 of the oestrous cycle, but not on days 10-16. There was no difference in the ED(50) or V(max) (maximal response) values between IGF-I and long R(3)-IGF-I. Neither anti-IGF-I nor anti-IGF-IR had significant effects on progesterone secretion, at any dose or day. Wortmannin and LY 294002 blocked IGF-I stimulated progesterone secretion, but PD 98059 was without effect. Finally, IGF-I (6 microg) infused into the ovary on day 7 in vivo significantly increased progesterone secretion within 45 min of infusion. The conclusions of this study are: (1) IGF-I has steroidogenic actions only on 'young' (days 4-7) pig corpora lutea; (2) endogenous IGF-I and IGFBP are insufficient to modulate progesterone secretion in vitro; and (3) the steroidogenic actions of IGF-I are mediated via PI-3-kinase.
Miller
E A
EA
Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA.
Ge
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Hedgpeth
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Gadsby
J E
JE
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004971:Estrus / Q000378:metabolism*; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D005498:Follicular Phase; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011374:Progesterone / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors; D015398:Signal Transduction; D034421:Sus scrofa / Q000378:metabolism*; D000077191:Wortmannin
D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007334:Insulin-Like Growth Factor I; D020929:Mitogen-Activated Protein Kinase Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011374:Progesterone; D017526:Receptor, IGF Type 1; D000077191:Wortmannin; C085700:long R(3)-insulin-like growth factor-I; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one