Binding Sites for IGF-I Identified on Theca Cells from Large Porcine Follicles
Theca from large porcine follicles (>8mm) were examined for specific IGF-I binding sites. Thecal membranes were prepared and then incubated overnight at 4°C with I-IGF-I with or without increasing concentrations of IGF-I, IGF-II and insulin. Specific high-affinity IGF-I binding sites were demonstrated. Scatchard analysis gave a curvilinear plot with a Ka for the high affinity sites of 1.97 ± 0.35 nM (binding capacity, 305.7±37.2 fmol/mg protein). Preferential binding was IGF-I>IGF-II>insulin. Interestingly, IGFs modulate steroidogenesis in porcine theca cells with a similar order of potency. These data demonstrate high affinity, low capacity binding of IGF-I to porcine thecal membranes and suggest that IGF-I and related peptides act on thecal steroidogenesis through IGF-I receptors.
KeywordsGranulosa Cell Follicular Fluid Theca Cell Scatchard Analysis Acanthosis Nigricans
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