Effect of oestradiol on ovarian oxytocin secretion rate and luteolysis in the ewe after ovarian auto-transplantation

The release of ovarian oxytocin and uterine prostaglandin (PG)F-2 alpha in response to an oestradiol stimulus was investigated. On Day 15 post-oestrus, ten ewes with ovarian auto-transplants (n = 5 per group) received an intra-muscular injection of either oestradiol benzoate (50 mu g) or vehicle. Blood samples were collected from the ovarian and jugular veins at 30 and 0 min before, and at 15-min intervals up to 540 min after, injection. The secretion rate of ovarian progesterone remained elevated in four of five treated ewes and in all control ewes, indicating the presence of a functional corpus luteum. Peripheral oestradiol concentrations were significantly (P < 0.001) higher in treated than in control ewes, The number of ewes that released pulses of ovarian oxytocin greater than or equal to 240 min following oestradiol benzoate injection was significantly (P < 0.05) greater than that in control ewes, Mean amplitude and area under both ovarian-vein oxytocin and jugular-vein 15 keto-13,14 dihydro prostaglandin F-2 alpha (PGFM) pulses were significantly increased in the treated ewes. These findings demonstrate that the administration of exogenous oestrogen provides a positive stimulus for the release of ovarian oxytocin and uterine PGF(2 alpha) in the ovarian auto-transplanted ewe.