Insulin-like growth factor-1 regulates the expression of luteinizing hormone receptor and steroid production in bovine granulosa cells.

Contents Luteinizing hormone LH plays important roles in follicular maturation and ovulation. The effects of LH are mediated by LH receptor (LHR) in the ovary. However, the factors that regulate the expression of LHR in bovine granulosa cells (GCs) are not well known. Insulin-like growth factor-1 (IGF-1) is known to play a key role in the acquisition and maintenance of functional dominance. To better understand the roles of LHR expression and IGF-1, we conducted three experiments to determine (i) mRNA expression of LHR in the GCs of developing follicles, (ii) the effects of IGF-1 on LHRmRNA expression in cultured GCs and (iii) the effects of IGF-1 on estradiol (E2), progesterone (P4) and androstenedione (A4) production by non-luteinized GCs. In experiment 1, small follicles (<6mm O) expressed lower levels of LHR than mid-sized follicles (6-8mm O) and large follicles (9mm O) expressed the highest levels of LHRmRNA (p<0.05). In experiment 2, IGF-1 (1 and 100ng/ml) increased (p<0.05) the expression of LHRmRNA in GCs from small and large follicles. In experiment 3, IGF-1 (0.1-100ng/ml) increased A4 and E2 in GCs from both small and large follicles but increased P4 only in large follicles. IGF-1 in combination with LH (0.1 and 1ng/ml) increased P4 and A4 in large follicles, and increased E2 and A4 in GCs of small follicles. These findings strongly support the concept that IGF-1 upregulates LHRmRNA expression as well as A4 and E2 production in GCs and that IGF-1 is required for determining which follicle becomes dominant and acquires ovulatory capacity.