Anastomosis of the ovarian vein to the hepatic portal vein in sheep induces ovarian hyperstimulation associated with increased LH pulsatility, but only in the absence of the contralateral ovary

In this study, two experiments were performed, the first of which examined the ovarian response in ewes that were subject to unilateral ovariectomy (U LO) at different intervals (0-14 days) after surgical anastomosis (AN) of t he ovarian vein to the mesenteric vein (n=7 ewes), or sham operation (SO; n =4 ewes). Hypertrophy and development of multiple follicular and luteal str uctures on AN ovaries were observed after ULO, while SO ovaries remained of normal size and appearance after ULO. The second experiment involving 11 e wes (five AN; six SO) aimed to clarify the mechanism by which AN following ULO-induced ovarian hypertrophy and increased follicle development. The res ults confirmed that there were more large (>5 mm) follicles on AN compared with SO ovaries; however, their rate of atresia was similar. Oestradiol and progesterone concentrations in follicular fluid of class 1 follicles (5-9 mm) were higher in AN ovaries than those in control follicles of the same s ize collected in the late follicular phase of an induced oestrous cycle. In AN ewes, intrafollicular progesterone concentrations increased while folli cular aromatase activity and intrafollicular oestradiol, inhibin A, follist atin and activin A concentrations all decreased as follicle size increased. Oestradiol and progesterone concentrations were substantially higher in ov arian venous blood than in hepatic venous blood, both in AN and SO ewes, wh ereas inhibin A levels were not significantly modified by passage through t he Liver in either group. Mean plasma LH concentration, and LH pulse freque ncy and amplitude increased markedly after AN but were not affected by SO. Plasma FSH showed only a small transient increase after AN, presumably due to the maintenance of inhibin feedback. Injection of prostaglandin F-2 alph a 4 days later did not further modify LH or FSH secretion in either group. Full ovariectomy (FO) 9-14 days after AN or SO increased LH secretion marke dly in SO ewes but to a lesser degree in AN ewes; FO induced a large and ra pid increase in FSH levels in both groups. In conclusion, AN of the ovary t o the liver via the mesenteric vein provides a useful model for studying th e feedback between the ovary and the hypothalamo-pituitary system and the m echanisms controlling follicle development. The present results indicate th at the pattern of LH secretion is an important factor controlling the termi nal phase of follicle development in the ewe.