Aetiology of attenuated luteal develop ment in prednisolone-induced eosinopenic ewes

Eosinophilic leukocytes infiltrate the wall of postovulatory ovine follicle s. The objective of this investigation was to assess a putative role of res ident eosinophils in the folliculo-luteal transition. Eosinophils accumulat ed 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 eos inophils were ablated by systemic administration of prednisolone following ovulation. Glandular dysfunction was related to a diminished angiogenic res ponse (quantitative image analysis of vascular space in histological specim ens and scanning electron microscopy of corrosion casts) during the luteini zation process. Vascular endothelial growth factor (VEGF) was localized by immunofluorescence microscopy to luteal eosinophils. It is suggested that V EGF of eosinophilic origin contributes to the neovascularization mechanism of corpora lutea in sheep.