PATTERN AND LOCALIZATION OF EXPRESSION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR AND ITS RECEPTOR FLT-1 IN THE OVINE PITUITARY-GLAND - EXPRESSION IS INDEPENDENT OF HYPOTHALAMIC CONTROL

The pituitary gland, a highly vascularised endocrine organ, contains p ermeable fenestrated endothelium that allows direct access of endocrin e cells to the hemal milieu. Vascular endothelial growth factor (VEGF) has a mitogenic effect on endothelial cells and renders the endotheli um more permeable. The following study investigated the expression of VEGF and its receptor flt-1 mRNA and protein in the pituitary gland of sheep. VEGF expression was localised, by in situ hybridisation and im munocytochemistry, mainly to the pars tuberalis/zona tuberalis (PT/ZT) region of the gland. No hybridisation signal was observed in the pars intermedia or pars nervosa. Reverse transcriptase-polymerase chain re action (RT-PCR)/Southern blotting confirmed the predominant expression of VEGF in the PT/ZT compared with the pars distalis (PD). Western bl ot analysis with the VEGF antibody revealed major (48 kDa) and minor ( 24 kDa) bands representing the monomer and dimer forms of VEGF and als o confirmed the differential expression of VEGF in the PT/ZT compared with the PD. Double immunocytochemistry with VEGF and prolactin or lut einising hormone-beta (LH-beta) antibodies demonstrated that the VEGF- secreting cells are not lactotrophs or gonadotrophs. However, co-local isation of VEGF with S-100 was observed in a proportion of cells sugge sting that some VEGF secreting cells are follicular stellate. Immunocy tochemistry with a flt-1 antibody confirmed the expression of this hig h affinity receptor for VEGF in endothelial cells across the pituitary gland. Immunocytochemistry with the VEGF antibody using pituitary gla nds from intact and hypothalamo-pituitary disconnected sheep demonstra ted comparable expression patterns suggesting that the regulation of b lood flow and vascular permeability in the pituitary gland is under lo cal regulation and is independent of hypothalamic input. (C) 1997 Else vier Science ireland Ltd.