Insulin-like growth factor I enhances gonadotropin-releasing hormone-stimulated luteinizing hormone release from bovine anterior pituitary cells.
The role of insulin-like growth factor I (IGF-I) in the release of luteinizing hormone (LH) is unclear in ruminants. In the present study, the effects of IGF-I on the release of LH stimulated by gonadotropin-releasing hormone (GnRH) were examined in primary cultures of bovine anterior pituitary (AP) cells, and the interaction between estradiol-17beta (E(2)) and IGF-I was characterized. GnRH(100nM)-stimulated LH release from the cultured cells was increased (P<0.05) 12, 24 and 36h after addition of IGF-I (250ng/ml), with a maximum at 12h (48.4ng/ml media versus 35.4ng/ml media in controls). IGF-I at concentrations of 25, 250 and 500ng/ml increased the release by 18.7, 24.2 and 28.9%, respectively (P<0.05), when compared with controls (37.2ng/ml media). E(2) (10nM), IGF-I (250ng/ml) and combined treatment of E(2) plus IGF-I also induced significant increases in LH release (P<0.05). The amounts of LH release after treatment with E(2) alone was 37.3% greater than with IGF-I alone (39.0ng/ml media versus 28.4ng/ml media) (P<0.05). When E(2) and IGF-I were added together (45.6ng/ml media), the release of LH was significantly greater than with either E(2) alone or IGF-I alone (P<0.05). E(2) (10nM) significantly (P<0.05) increased the amount of GnRH bound to the cells by 51.6% when compared with controls, however, IGF-I (250ng/ml) failed to increase GnRH binding. These results show that IGF-I enhances GnRH-stimulated LH release without changing the number of GnRH receptors in cattle, and IGF-I interacts with E(2) to increase the response to GnRH.
Hashizume
T
T
Faculty of Agriculture, Iwate University, Ueda 3, Morioka, Japan. hashi@iwate-u.ac.jp
Kumahara
A
A
Fujino
M
M
Okada
K
K
D000818:Animals; D002417:Cattle / Q000502:physiology*; D002478:Cells, Cultured; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011966:Receptors, LHRH / Q000378:metabolism
D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone