Altered porcine ovarian IGF-I and steroid hormone synthesis in response to glucocorticoids

The objective of this project was to determine if glucocorticoids can influence IGF-I synthesis and/or IGF-mediated actions in the porcine ovary. In one investigation granulosa cells (GC) were retrieved from gilts at the later stages of the estrous cycle including day 14, 18 and 20 prior to the LH surge and luteinized GC on day 21. The cells were cultured serum free with increasing concentrations (0, 1, 10, and 100 {dollar}mu{dollar}g/ml) of cortisol (C) and supplemented with FSH and androsteredione (A), with or without IGF-I. Cellular IGF-I, progesterone (P{dollar}sb4{dollar}) and estradiol-17{dollar}beta{dollar} (E{dollar}sb2{dollar}) production was determined and cell proliferation assessed. In a second investigation, gilts were treated with ACTH to elevate endogenous glucocorticoid levels during the luteal phase (day 9-13) while controls received saline. The ovaries were removed on day 14 and 18; follicular fluid (FF) was collected from individual follicles to determine the IGF-I, IGF-binding protein (IGFBP) and steroid hormone (C, P{dollar}sb4{dollar}, E{dollar}sb2{dollar}, A) profile. The GC were cultured with gonadotrophin and/or IGF-I support to evaluate IGF-I, P{dollar}sb4{dollar} and E{dollar}sb2{dollar} production.; Granulosa cell IGF-I and steroid synthesis generally increased (P {dollar}<{dollar} 0.05) with follicle development. Direct exposure to high C concentrations altered both IGF-I synthesis and action; the effects, however, were dependent on the stage of the cycle. Cortisol lowered (P {dollar}<{dollar} 0.05) ICF-I production by GC recovered on days 18, 20. and 21 and suppressed (P {dollar}<{dollar} 0.05) IGF-stimulated P{dollar}sb4{dollar} synthesis at all stages. Cortisol also reduced (P {dollar}<{dollar} 0.05) IGF-stimulated E{dollar}sb2{dollar}, synthesis on day 14, but enhanced (P {dollar}<{dollar} 0.05) FSH-stimulated P{dollar}sb4{dollar} production by GC from day 14 and day 18. These effects could not be attributed to differences in cell numbers since C did not alter IGF-stimulated GC proliferation. In the second investigation, FF from ACTH-treated gilts was characterized by elevated (P {dollar}<{dollar} 0.05) C levels on day 14 and lower (P {dollar}<{dollar} 0.05) E{dollar}sb2{dollar} at all stages; IGF-I values were reduced (P {dollar}<{dollar} 0.05) on day 18, although IGFBP levels were not significantly altered. The IGF-stimulated P{dollar}sb4{dollar} production (with or without FSH) was attenuated in GC from the ACTH group on day 14, but IGF-1 synthesis was unaffected. By day 18, GC regained their responsiveness to IGF-I, however, IGF-I synthesis was significantly lower (P {dollar}<{dollar} 0.05) along with P{dollar}sb4{dollar} and E{dollar}sb2{dollar} production. These results demonstrate that high glucocorticoid concentration can specifically disrupt IGF-I synthesis and IGF-mediated actions in porcine GC under both in vitro and in vivo conditions.