Effects of prolactin on conceptus survival and uterine secretory activity in pigs

Abstract

Hypoprolactinaemia was induced by bromocriptine (CB154; 100 mg/day) which decreased circulating prolactin by 40% (P < 0.06), but did not affect conceptus survival at Day 25 when administered on Days 10-16 when compared to saline:ethanol-treated control gilts. Bromocriptine or vehicle was administered to cyclic gilts on Days 10-11, oestradiol valerate was injected on Day 11 and uterine flushings were collected on Day 12. Total recoverable protein and uteroferrin in uterine flushings were not affected by treatment. However, leucine aminopeptidase activity (P < 0.02) and total recoverable Ca2+, Na+, K+ and Cl- (P < 0.05) were decreased in uterine flushings of gilts that received bromocriptine, suggesting that hypoprolactinaemia decreased general secretory activity of the endometrial epithelium and modulated ionic changes, respectively, in the uterine environment of pigs. Subcutaneous administration of pig prolactin (1 mg/12 h) increased (P < 0.001) serum prolactin 4.5-fold. The interaction between hyperprolactinaemia and progesterone, without oestrogen, on components of uterine flushings were determined using gilts that received progesterone (200 mg/day) and prolactin or saline on Days 4-14 after ovariectomy on Day 4. On Day 15, there were no differences (P > 0.05) in any of the uterine secretory components measured. Hyperprolactinaemia (1 mg pig prolactin on Days 6-11) enhanced overall uterine secretory response on Day 12 to oestradiol (5 mg) administered on Day 11 compared to gilts that received 1 ml saline on Days 6-11 of the oestrous cycle. Total recoverable protein and leucine aminopeptidase activity were greater (P < 0.05) for oestradiol-treated gilts, but effects of prolactin were not significant. Total recoverable protein and leucine aminopeptidase activity were greater (P < 0.05) for oestradiol-treated gilts, but effects of prolactin were not significant. Total recoverable glucose (P < 0.01), PGF-2.alpha. (P < 0.02), uteroferrin (P < 0.01) and specific activity of uteroferrin (P < 0.001) were increased by prolactin and oestradiol, but not oestradiol alone. Calcium (P < 0.05), chloride (P < 0.05) and potassium (P < 0.01) were increased in response to oestradiol. These results indicate an interaction between oestradiol and prolactin, but not progesterone and prolactin, which enhances secretion of some products of the pig uterine endometrium.