Effects of insulin-like growth factor I and insulin on proliferation and on basal and luteinizing hormone-induced steroidogenesis of bovine thecal cells: involvement of glucose and receptors for insulin-like growth factor I and luteinizing hormone.
The objective of the present study was to determine the effects of IGF-I and insulin on cell proliferation, LH receptors, and basal and LH-induced progesterone and androstenedione production by bovine thecal cells. Cells from large (> or = 8mm) bovine follicles were cultured for 1 or 2 d in medium containing 10% fetal calf serum (FCS) and treated for 1 or 2 d in serum-free medium with IGF-I, insulin, and(or) LH. Treatment with 30 and 100 ng/mL of IGF-I for 1 or 2 d increased thecal cell numbers in the absence of LH regardless of whether treatments were initiated after 1 or 2 d of exposure to 10% FCS. Co-treatment with LH reduced the stimulatory effect of IGF-I on thecal cell numbers. Insulin at 10 and 100 ng/mL increased cell numbers in the presence of LH. Both IGF-I and insulin were ineffective at stimulating thecal cell progesterone or androstenedione production in the absence of LH. However, IGF-I and insulin increased (P < .05) androstenedione and progesterone production in the presence of LH. Alone, LH had little or no effect on androstenedione and progesterone production, whereas in the presence of 30 and 100 ng/mL IGF-I or 1 to 100 ng/mL insulin, LH stimulated (P < .05) androstenedione production. The stimulatory effects of IGF-I on cell proliferation and progesterone production were not detected in the presence of 100 ng/mL insulin. However, co-treatment with various doses of IGF-I and 100 ng/mL insulin further increased androstenedione production above that seen with insulin alone. In glucose-deficient medium, 25 to 75 mg/dL of glucose increased (P < .05) thecal cell proliferation, progesterone production, and androstenedione production. In the absence or presence of glucose, insulin (100 ng/mL) increased (P < .05) thecal cell proliferation, progesterone production, and androstenedione production. Treatment with 3, 10, or 100 ng/mL LH had no effect (P > .10) on the numbers of IGF-I binding sites on thecal cells but increased (P < .05) androstenedione production. Treatment with 10 and 100 ng/mL IGF-I increased (P <.01) numbers of LH/hCG binding sites. These results indicate that IGF-I and insulin may each play a significant role in thecal cell mitogenesis and LH-induced thecal cell steroidogenesis during follicular development in cattle and that glucose enhances these effects. Furthermore, the synergism between IGF-I and LH on increasing steroidogenesis does not seem to be mediated through increased binding sites for IGF-I in bovine thecal cells but rather, in part, through increased binding sites for LH.
Stewart
R E
RE
Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
Spicer
L J
LJ
Hamilton
T D
TD
Keefer
B E
BE
D000735:Androstenedione / Q000096:biosynthesis; D000818:Animals; D002417:Cattle; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D005947:Glucose / Q000032:analysis / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D007457:Iodine Radioisotopes; D007986:Luteinizing Hormone / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000096:biosynthesis; D011863:Radioimmunoassay / Q000662:veterinary; D017526:Receptor, IGF Type 1 / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D011974:Receptors, LH / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D013799:Theca Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D006063:Chorionic Gonadotropin; D007328:Insulin; D007457:Iodine Radioisotopes; D011974:Receptors, LH; D000735:Androstenedione; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D017526:Receptor, IGF Type 1; D005947:Glucose