Anastomosis between ovarian and mesenteric veins in sheep: induction of a physiological hyperstimulation of the ovary.

Progesterone (P4) and estradiol 17 beta are essential for the dialogue between the ovary and the hypothalamohypophysial system. Immunization against steroids, although a valuable tool, displays limits. We propose a straightforward method to suppress steroids from the peripheral circulation by using the liver to catabolize steroids, through an anastomosis of the ovary to the mesenteric vein. Twelve mature cycling Ile-de-France ewes were unilaterally ovariectomized during the breeding season and subsequently randomly assigned to be anastomosed (n = 6; A) or sham-operated (n = 6; SO) on Day 10 of a synchronized estrous cycle. The ovarian vein was anastomosed to the superior mesenteric vein and all collateral veins to the ovarian vein were ligatured. Sham-operated ewes had only their collateral vein ligatured without anastomosis. Four days following surgery, ewes from both treatments were injected with PGF-2 alpha and autopsied between 9 and 14 days following surgery. Blood progesterone and estradiol 17 beta were measured daily from Day 4 before surgery until 7 days after castration. Estradiol levels measured at the level of the ovarian vein indicated that anastomosis allowed normal ovarian activity in all but 1 ewe in which collateral veins to the ovarian duct had developed. In the 5 A ewes, progesterone in peripheral blood decreased to low levels the day following surgery but this fall was not accompanied by an increase in estradiol. Estradiol levels measured at the output of the liver from hepatic vein were lower in A ewes (46.6 pg/ml) than in the ovarian vein of SO ewes (334.1 pg/ml). Ovarian hypertrophy was observed in 5 A ewes in which numerous large follicles were observed. These results indicate that the experimental model is functional and permits the study of the stimulation and hyperstimulation of the ovary and the control of the terminal follicular growth in the endocrine environment of the animal itself.