Insulin-like growth factor II (IGF-II) inhibits insulin-like growth factor binding protein I (IGFBP-1) production in luteinized human granulosa cells with a potency similar to insulin-like growth factor I (IGF-I) and higher than insulin.

Abstract

Insulin-like growth factor binding protein I (IGFBP-I) is produced by human granulosa cells and may be important in follicular development. Production of IGFBP-I in human granulosa cells is under inhibitory control of insulin and insulin-like growth factor-I (IGF-I). It had not been known if IGF-II affected IGFBP-I production in these cells. We examined the effect of IGF-II on IGFBP-I production in human granulosa cells and compared this effect of IGF-II to similar effects of insulin and IGF-I. Human granulosa cells were obtained during in vitro fertilization and plated at a density of 10(5) cells/mL in McCoy 5A tissue culture medium supplemented with 10% fetal calf serum. After 48 h of preincubation at 37 C, 90% humidity, 5% CO2, the medium was removed, and serum-free medium was added. After 24 h of incubation in the serum-free medium, the medium was removed, cells were washed, and new serum-free medium supplemented with various concentrations of insulin, IGF-I, or IGF-II was added. After 24 h of incubation with insulin, IGF-I, or IGF-II, the medium was removed and frozen at-20 C until assayed for IGFBP-I. IGFBP-I was measured using kits from Diagnostic System Laboratories, Webster, Texas. Concentrations of IGFBP-I in the medium were 4.4 +/- 1.7 ng/mL for control cells; 3.0 +/- 0.8, 3.0 +/- 0.7, 3.1 +/- 0.7, 1.8 +/- 0.5, and 1.1 +/- 0.3 ng/mL for 1, 10, 10(2), 10(3), and 10(5) ng/mL insulin respectively; 1.4 +/- 0.6, 2.1 +/- 0.5, 0.3 +/- 0.1, 0.1 +/- 0.02, and 0.01 +/- 0.02 ng/mL for 0.5, 1, 5, 10, and 10(2) ng/mL of IGF-I, respectively; and 2.3 +/- 2.2, 1.2 +/- 0.8, 0.9 +/- 0.3, 0.7 +/- 0.2, and 0.04 +/- 0.02 ng/mL for 0.5, 1, 5, 10, and 10(2) ng/mL of IGF-II, respectively. Concentration of IGFBP-I in the medium collected from cells incubated with hormones was statistically lower than that for control cells starting at 10(3) ng/mL of insulin (P < 0.05), 0.5 ng/mL of IGF-I (P < 0.05) and 1 ng/mL of IGF-II (P < 0.05). Within the range of hormone concentrations tested, the P-values (independent groups t-test) never reached less than 0.01 levels for insulin, but reached this level at 5 ng/mL for both IGF-I and IGF-II. We conclude that IGF-II inhibits IGFBP-I production in luteinized human granulosa cells in a dose-dependent manner and with potency similar to IGF-I and higher than insulin. Further studies are needed to determine the physiological significance of this and other effects of IGF-II in the human ovary in both normal and pathological states.