Expression of the insulin-like growth factor and insulin systems in the luteinizing macaque ovarian follicle

Abstract

Objective: To determine intrafollicular hormone levels and characterize the mRNA expression of the insulin-like growth factor (IGF) receptors, IGF binding proteins (IGFBP), and pregnancy-associated plasma protein-A (PAPP-A) in granulosa cells before and after an ovulatory hCG stimulus.

Design: Experimental animal study.

Setting: Academic medical center.

Animal(s): Adult rhesus macaques.

Intervention(s): Animals received exogenous FSH to promote the development of multiple preovulatory follicles. Follicles were aspirated before (0 hours) or 3, 6, 12, or 24 hours after an ovulatory hCG bolus.

Main outcome measure(s): IGF1, IGF2, and insulin levels in follicular fluid were determined by radioimmunoassay. Messenger RNA (mRNA) levels in granulosa cells were determined by real-time reverse transcriptase-polymerase chain reaction. IGFBPs and PAPP-A in follicular fluid were determined by Western blot analysis and enzyme-linked immunosorbent assay.

Result(s): IGF1, IGF2, and insulin in follicular fluid did not change during luteinization. IGF1R, IGFBP1, and IGFBP2 mRNAs were unchanged by hCG. IGF2R, IGFBP3, -5, and -6 and PAPP-A mRNA levels increased after hCG administration, while insulin receptor and IGFBP4 mRNA levels decreased after hCG administration. IGFBP3 and -6 and PAPP-A protein increased after hCG administration.

Conclusion(s): Dynamic changes in the expression of the IGFBPs and PAPP-A suggest tight regulation of IGF action during ovulation and corpus luteum formation.