INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 INHIBITS PORCINE GRANULOSA-CELL FUNCTION IN-VITRO

Recombinant human insulin-like growth factor binding protein-3 (rhIGFB P-3) effects on basal, insulin-like growth factor I (IGF-I)-, and foll icle-stimulating hormone (FSH)-stimulated progesterone (P-4) secretion and [H-3]aminoisobutyric acid (AIB) uptake by primary porcine granulo sa cells (MDGs) and MDGs that have been passaged once (MDGp1) were ass essed. Cells were treated concurrently or were preincubated with rhIGF BP-3 followed by treatment. rhIGFBP-3 had no effect on MDG or MDGp1 ce ll numbers after 24 h. Cotreatment with rhIGFBP-3 inhibited P-4 secret ion after treatment with FSH, IGF-I, and FSH plus IGF-I. FSH did not s timulate [H-3]AIB uptake. However, the IGF-I-stimulated increase in [H -3]AIB uptake was completely prevented by concurrent treatment with IG FBP-3. Preincubation of MDGp1 cells with IGFBP-3 dose dependently inhi bited FSH- and IGF-I-stimulated P-4 secretion. This inhibition was ass ociated with increased cell association of the binding protein and inc reased IGF-I binding to the cells. These results indicate that IGFBP-3 is inhibitory to a variety of crucial functions in porcine granulosa cells, supporting a role for it in the regulation of granulosa cell fu nction.