Aetiology of attenuated luteal development in prednisolone-induced eosinopenic ewes

Eosinophilic leukocytes infiltrate the wall of postovulatory ovine follicles. The objective of this investigation was to assess a putative role of resident eosinophils in the folliculo luteal transition. Eosinophils accumulated where new blood vessels were evident along connective tissue trabeculae that pervaded the parenchyma of formative corpora lutea. Mid-phase function of corpora lutea (progesterone output) was suppressed in ewes in which eosinophils were ablated by systemic administration of prednisolone following ovulation. Glandular dysfunction was related to a diminished angiogenic response (quantitative image analysis of vascular space in histological specimens and scanning electron microscopy of corrosion casts) during the luteinization process. Vascular endothelial growth factor (VEGF) was localized by immunofluorescence microscopy to luteal eosinophils. It is suggested that VEGF of eosinophilic origin contributes to the neovascularization mechanism of corpora lutea in sheep.