FASTING STIMULATES VEGF mRNA EXPRESSION AND STEROIDOGENESIS IN PIG CORPORA LUTEA

VEGF is an important regulator of both angiogenesis and vascular permeability and it appears to be involved in the development of corpus luteum as well as in its regression in several species. VEGF production has been shown to be modulated by a variety of stimuli, among which nutrient shortage seems to play an important role. Recently we have demonstrated that short-term fasting in gilts increases VEGF concentrations in follicular fluid and VEGF mRNA levels in theca layer (Galeati et al., Reproduction, 126:647-652, 2003). This study was aimed at verifying whether fasting influences VEGF mRNA expression as well as steroidogenesis in pig CL. Eight prepubertal gilts were treated with 1250 IU eCG followed 60 h later by 750 IU hCG in order to induce follicle growth and ovulation. Five days after hCG treatment, the animals were divided into two groups: group A - normal alimentation with a commercial diet, group B - 72 h of fasting with water available at all times. Ovaries were collected 8 days after hCG treatment and the single CLs (10/sow) were cut in two halves. One half was weighed, homogenized in PBS (0.1 g/ml) and stored at -20°C until measurement of steroid content (progesterone, testosterone and estradiol-17beta); the second half was treated with Tri-Pure (50 mg/ml) and stored at -80°C until VEGF mRNA levels determination. Fasting significantly (P<0.01) increased VEGF mRNA content (190.12+/-21.39 vs 108.96+/-10.68 arbitrary units in fasted and normally fed animals, respectively), as well as steroid concentrations (P4: 30.5+/-1.47 vs 20.9+/-0.87 ng/mg; E2: 0.57+/-0.04 vs 0.390+/-.01 pg/mg; T: 23.01.78 vs 14.20+/-0.78 pg/mg; P<0.001). The increase in VEGF mRNA induced by fasting likely compensates the nutrients reduction through the formation of new vessels, thus favouring the supply of substrates for steroidogenesis.