Insulin-like growth factor (IGF)-I, ICF-I receptor, and IGF binding protein-3 messenger ribonucleic acids and protein in corpora lutea from prostaglandin F-2 alpha-treated gilts

Insulin-like growth factor-I (IGF-I) is produced within the porcine corpus luteum (CL) and is thought to play an autocrine/paracrine role in CL develo pment/function during the early luteal phase, This study examines the hypot heses that the luteolytic actions of prostaglandin F-2 alpha (PGF(2 alpha)) during the early luteal phase may involve either a decrease in IGF-I or IG F receptor (IGF-IR), or an increase in IGF binding protein (IGFBP)-3, expre ssion, any of which could interfere with the luteotropic actions of ICF-I i n this tissue. Cycling gilts were treated twice daily with PGF(2 alpha) (or saline) on Days 5-9 of the cycle to induce premature luteolysis. Ct were c ollected on Days 6-9, and RNA, protein, or progesterone was extracted. By s lot blot analysis, steady-state levels of ICF-I and IGFBP-3 mRNA were not d ifferent in PGF(2 alpha)-treated vs. control animals; however, IGF-IR mRNA was increased in treated animals on Day 9, No changes in IGF-I content (ng/ CL measured by RIA) were observed with respect to treatment. According to l igand blot analysis, the levels of IGFBP-3 increased on Day 6 and decreased on Days 8-9, while IGFBP-2 was higher on Days 6-7 and decreased on Day 9 i n treated animals. ICF-IR levels, determined from Western blots, were highe r on Day 7 (P < 0.05) and lower on Day 9 in PGF(2 alpha)-treated animals vs . control animals (P < 0.05). In conclusion, PGF(2 alpha)-induced premature luteolysis was associated with an increase in steady-state levels of ICF-I R mRNA, but it did not appear to be linked to changes in mRNA levels for IC F I or IGFBP-3, However, since IGFBP-2 and -3 protein levels increased earl y in the treatment period (Days 6-7), it is possible that they may mediate the luteolytic actions of PGF(2 alpha) by sequestering ICF-I and preventing its interaction with the IGF-IR.