Stimulatory and synergistic effects of luteinising hormone and insulin like growth factor 1 on the secretion of vascular endothelial growth factor and progesterone of cultured bovine granulosa cells

Vascular endothelial growth factor (VEGF) is the most important factor in the regulation of angiogenesis. Associated with luteinisation and formation of corpus luteum (CL) are alterations in luteal vascularity. The aim of the study was to test under in vitro conditions the stimulation of VEGF and progesterone (P) secretion of bovine granulosa cells by LH, IGF1 (insulin like growth factor) or by factors known to be produced by luteinised granulosa cells or in the early CL. Localisation of VEGF protein in preovulatory follicle and early CL were achieved by immunohistochemistry. LH and IGF1 stimulated dose dependently and significantly P and VEGF when tested alone. Both hormones added simultaneously had clear additive and even more interesting far greater (synergistic) effects on P with LH (0.1 ng/ml) plus 5 or 10 ng IGF1. In contrast, VEGF was stimulated only additively with 0.1 ng/ml of LH plus 5 or 10 ng IGF1. But with the higher dose of LH (1 ng/ml) additionally to the additive effect a tendency for a synergistic action (which was significant with 1 ng LH plus 5 ng IGF1/ml) was observed. Endothelin, oxytocin, progesterone, atrial natiuretic peptide, angiotensin II, prostaglandin F2αα, prostaglandin E₂, cortisol, fibroblast growth factor 1 and 2 and growth hormone showed no effect neither on P nor on VEGF. Tumour necrosis factor α (TNFα) stimulated (P<0.05) VEGF with 10 or 100 ng/ml but not P. TPA (12-0 tetra decaenoyl-phorbol-13-acetate) or Ca²⁺ ionophore did not show a stimulatory effect in contrast to forskolin which increased P and VEGF secretion dose dependently. The VEGF protein was localised in follicle (granulosa cells, theca cells and some endothelial cells) and early (about 24 h after ovulation) CL (granulosa-lutein cells and endothelial cells). The same signalling pathway by stimulation of cAMP production and proteinkinase A activation for luteinisation and neo-vascularisation demonstrates a close temporal and spatial relationship of these normal physiological processes.