Insulin-like growth factor-II stimulates steroidogenesis in cultured bovine thecal cells.
The objective of the present study was to determine the effects of insulin-like growth factor-II (IGF-II) on luteinizing hormone (LH)-induced progesterone and androstenedione production by bovine thecal cells and compare it to that of insulin and IGF-I. Cells from large (>7.9 mm) bovine follicles were collected and cultured for 2 days in the presence of 10% fetal calf serum. Then cells were cultured for an additional 1 or 2 days in serum-free medium with various doses of recombinant human IGF-II, bovine LH (30 ng/ml), IGF-I, and(or) insulin. Cell numbers were determined at the end of treatments via Coulter counting and used to correct steroid production data. In the presence of LH, 1-day treatment with 3-300 ng/ml of IGF-II had no significant effect on progesterone or androstenedione production, whereas 2-day treatment with 30, 100 and 300 ng/ml of IGF-II increased (P < 0.05) both progesterone and androstenedione production by 2-3-fold. The estimated effective dose of IGF-II stimulating 50% of the maximal steroidogenic response was calculated to be 25 ng/ml. In the absence of LH, 2-day treatment of IGF-I or -II had no effect on thecal androstenedione production but increased (P < 0.05) thecal progesterone production. In the presence of LH, 100 ng/ml of IGF-I increased progesterone and androstenedione production to a greater degree than did 100 ng/ml of IGF-II. Maximal effects of IGF-I and insulin on thecal steroidogenesis were similar and were not additive. Anti-IGF type I receptor antibodies attenuated (P < 0.05) the stimulatory effect of both IGF-I and IGF-II on thecal cell steroidogenesis. Use of radioligand assays demonstrated that specific receptors for (125)I-IGF-II existed in thecal cells with a 25 ng/well of IGF-II causing 50% inhibition of binding. IGF-I cross-reactivity with (125)I-IGF-II receptors averaged 3% whereas cross-reactivity of IGF-II with (125)I-IGF-I receptors averaged 114%. These results indicate that the stimulatory effects of IGF-II on thecal cell steroidogenesis is mediated by IGF type I receptors and thus IGF-II, like IGF-I, may play a significant role in thecal cell steroidogenesis during follicular development.
Spicer
L J
LJ
Department of Animal Science, Oklahoma State University, Stillwater, OK 74078, USA. igfleo@okstate.edu
Voge
J L
JL
Allen
D T
DT
D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D005260:Female; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D011374:Progesterone / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011974:Receptors, LH / Q000378:metabolism*; D013799:Theca Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D007328:Insulin; D011974:Receptors, LH; D000735:Androstenedione; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D007986:Luteinizing Hormone; D017526:Receptor, IGF Type 1