OVARIAN INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-2 MESSENGER-RNA LEVELS CHANGE OVER THE ESTROUS-CYCLE

The expression of the putative FSH antagonist, IGFBP-2, in the rat ova ry during the estrous cycle was investigated. A single 1.8 kb IGFBP-2 mRNA transcript was identified in all ovaries examined and the transcr ipt was localized to theca interstitial (TIC), secondary interstitial (SIC) and surface epithelial cells. Relatively high levels of IGFBP-2 mRNA were present in TIC of dominant follicles, e.g., from selection t hrough ovulation; however, the signal intensity changed over the cycle : E 0200 h (selection stage) = 79.7 +/- 4.3; E 1000 h = 33.3 +/- 4.2; D1 1100 h = 100 +/- 7.5; DII = 98.9 +/- 5.6; P 1000 h = 78.2 +/- 3.2; P 2000 h (preovulatory stage) = 92 +/- 4.9. The signal intensity fell progressively to undetectable levels as the TIC differentiated into th eca lutein cells during ovulation and luteinization; E 0200 h (ovulati on) = 66.7 +/- 3.5; E 1000 h (early luteinization) = 40.2 +/- 2.8; DI 1100 h (late luteinization) = nondetectable. No hybridization signal w as detected in corpora lutea undergoing luteolysis. A positive hybridi zation signal was evident in TIC of atretic graafian follicles over th e cycle, but the signal was too variable to quantify. The SIC were pos itive for IGFBP-2 mRNA but the signal intensity changed over the cycle , particularly between estrus and diestrus I: E 0200 h = 100 +/- 6.9; E 1000 h = 27.9 +/- 2.3; DI = 91.6 +/- 6; DII = 54.3 +/- 4.2; P 1000 h = 66.5 +/- 1.9; P 2000 h = 54.3 +/- 3.2. The signal intensity in the surface epithelium (SE) appeared roughly constant throughout the cycle , except at E 1000 h when it increased sharply to maximal levels. Thes e results indicate that cyclical changes in IGFBP-2 mRNA levels occur in the interstitial and surface epithelial cells during the normal est rous cycle. Consequently, we speculate that inducible and tissue speci fic expression of IGFBP-2 may play an autocrine/paracrine role in modu lating IGF responses in ovarian target cells during folliculogenesis, ovulation and luteogenesis.