Beta-endorphin in uterine secretions of pseudopregnant and ovariectomized, ovarian steroid-treated gilts.

Levels of beta-endorphin-like immunoreactivity (beta END-LI) in uterine secretions were studied in pseudopregnant and ovariectomized gilts treated with ovarian steroids. Pseudopregnancy was induced in 7 gilts by daily injection of estradiol valerate (5 mg/day) between days 11 and 15 of the estrous cycle. Between days 60 and 90 of pseudopregnancy, uterine secretions were collected by flushing the uterus with 0.9% saline. Uterine flushings were extracted with a Sep-Pak C-18 column and assayed for beta END-LI by a specific RIA. The RIA cross-reacted only with beta-lipotropin (15%). Significant amounts of total immunoreactive beta END-LI were detected in the uterine flushings. The inhibition curve for extracts was parallel to the standard END inhibition curve. Extracted uterine flushings were applied to a Sephadex G-50 column. Three peaks of immunoreactive beta END-LI were detected. One peak eluted at the void volume. The second peak eluted at a Kav of 0.21, which was near the Kav of a lipotropin standard (0.23). The highest peak (Kav = 0.53) eluted similar to standard END (Kav = 0.51). In the second experiment, 12 gilts were ovariectomized on day 4 of the estrous cycle and randomly assigned to 4 groups of 3 gilts each. Each group received 1 of the following daily injections: vehicle (corn oil), 0.1 mg 17 beta-estradiol (E2), 200 mg progesterone (Prog), or a combination of E2 and Prog (E2 + Prog). After treatment for 30 days, beginning on the day of ovariectomy, the uterine flushings were assayed for beta END-LI and total protein. Treatment with Prog increased (P less than 0.05) total beta END-LI 532% (12.4 ng) compared to corn oil treatment (2.3 ng), and levels were significantly higher than with E2 (2.9 ng) or E2 + Prog treatment (5.1 ng). Opiate receptor assay showed that extracts of uterine flushing had a displacement curve parallel to that of standard porcine beta END. Results suggest that significant amounts of immunoreactive beta END-LI are present in uterine secretions of gilts and that the accumulation of beta END-LI is influenced by ovarian steroids.