EFFECTS OF GROWTH-HORMONE AND GONADOTROPIN ON THE INSULIN-LIKE GROWTHSYSTEM IN THE PORCINE OVARY

The effects of growth hormone (GH) +/- pregnant mare's serum gonadotro pin (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 gil ts were determined. Steroids in FFl were also quantified. In the first experiment, GH, given for either 20 or 40 days, caused a distinct (th reefold, p < 0.05) increase in IGF-I in both serum and FFl with no cha nge in the FFl:serum ratio (0.65). Effects of GH on IGF-II were opposi te, 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 treatm ent. 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 3 1%, respectively (p < 0.001). FFl IGFBP-3 was increased to a similar e xtent by GH (p < 0.005), hut IGFBP-2 was not affected. Neither progest erone (P-4) nor estradiol(E(2)) was affected by treatment with GH. How ever, androstenedione (A(4)) was decreased by 20-day and 40-day GH tre atment relative to the respective controls (p < 0.05). In the second e xperiment, PMSG resulted in a modest (28%) increase in intrafollicular IGF-I (p < 0.06). However, the FFl:serum ratio increased significantl y (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 expe riment, PMSG did not affect serum levels of either IGFBP or FFl IGFBP- 3; however, it decreased FFl IGFBP-2 to 25% of central values (p < 0.0 5). The PMSG increased A(4) and E(2) but not P-4 concentrations in FFl . Pretreatment with GN antagonized the effects of PMSG on A(4) and E(2 ) (p < 0.001 and p < 0.05, respectively) and IGFBP-2. Northern blots f or IGF-I and -II mRNA showed multiple transcripts similar to those see n in representative control tissues. In quantitative slot-blot analysi s, the expression of IGF-I and IGF-II mRNAs in hormone-treated animals paralleled the results for FFl peptide levels; however, changes in IG F mRNAs were not statistically significant In the first experiment, IG FBP-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 IGFB P mRNAs was found in the second experiment. In summary, these results indicate that there is a resident ovarian IGF system that is hormonall y responsive. While the effects of PMSG appear to be ovary selective, the effects of GH were generalized.