The effects of growth hormone (GH) ± pregnant mare's serum gonadotropin (PMSG) on levels of insulin-like growth factor (IGF)-I and -II and IGF binding protein (BP)-2 and -3 in serum and follicular fluid (FFl) and on the expression of their mRNA in the ovaries of prepubertal gilts were determined. Steroids in FFl were also quantified. In the first experiment, GH, given for either 20 or 40 days, caused a distinct (threefold, p < 0.05) increase in IGF-I in both serum and FFl with no change in the FFl:serum ratio (0.65). Effects of GH on IGF-II were opposite, with a drop in circulating and FFl levels (p < 0.05). In contrast to data for IGF-I, FFl levels were higher than those in serum for IGF-II (1.42, FFl serum); IGF-II levels and the ratio fell after GH treatment. GH for either 20 days or 40 days increased serum IGFBP-3 to 140% and 250% of control values while decreasing serum IGFBP-2 by 46% and 31%, respectively (p < 0.001). FFl IGFBP-3 was increased to a similar extent by GH (p < 0.005), but IGFBP-2 was not affected. Neither progesterone (P4) nor estradiol (E2) was affected by treatment with GH. However, androstenedione (A4) was decreased by 20-day and 40-day GH treatment relative to the respective controls (p < 0.05). In the second experiment, PMSG resulted in a modest (28%) increase in intrafollicular IGF-I (p < 0.06). However, the FFl:serum ratio increased significantly (p < 0.05). In contrast, PMSG resulted in a modest decline in IGF-II in FFl that was accompanied by a significant decline in the FFl:serum ratio (1.27 ± 0.03 vs. 1.04 ± 0.03, p < 0.05). In the second experiment, PMSG did not affect serum levels of either IGFBP or FFl IGFBP-3; however, it decreased FFl IGFBP-2 to 25% of control values (p < 0.05). The PMSG increased A4 and E2 but not P4 concentrations in FFl. Pretreatment with GH antagonized the effects of PMSG on A4 and E2 (p < 0.001) and p < 0.05, respectively) and IGFBP-2. Northern blots for IGF- I and -II mRNA showed multiple transcripts similar to those seen in representative control tissues. In quantitative slot-blot analysis, the expression of IGF-I and IGF-II mRNAs in hormone-treated animals paralleled the results for FFl peptide levels; however, changes in IGF mRNAs were not statistically significant. In the first experiment, IGFBP-3 mRNA was modestly decreased (23%, p < 0.05) by GH, but there was no effect on IGFBP-2 mRNA. No significant change in either of the IGFBP mRNAs was found in the second experiment. In summary, these results indicate that there is a resident ovarian IGF system that is hormonally responsive. While the effects of PMSG appear to be ovary selective, the effects of GH were generalized.
All Science Journal Classification (ASJC) codes
- Reproductive Medicine
- Cell Biology