Uterine metabolic activity and steroid receptor concentrations in response to suppressed secretion of PRL in anestrous mink

Two experiments were conducted to evaluate the effects of bromocriptine, melatonin (MLT), and 17 beta-estradiol (E2) on uterine physiology in mink (Mustela vison). In Expt. 1, summer-anestrous mink were injected sc daily with 2 mg bromocriptine or vehicle (n = 20 each) for 14 days. On Day 14, both groups were divided into two subgroups and injected sc with either 100 micrograms E2 or vehicle. Mink were bled immediately prior to euthanasia (24 hr after E2) and the sera analyzed for prolactin (PRL), E2 and progesterone (P4). At necropsy, aliquots of uterine tissue (n = 5) were used to measure in vitro oxidation of [14C]glucose, incorporation of [3H]thymidine into DNA and [14C]leucine into protein, and nuclear concentrations of estrogen receptor (ER) and P4 receptor (PR). In Expt. 2, anestrous mink were assigned to one of two treatment groups or a control group (n = 5 each). In mid-summer, groups 1 and 2 were implanted with 10 mg Silastic MLT implants. Seventeen weeks later, mink in group 1 received 100 micrograms E2 (sc) while group 2 and nonimplanted controls (group 3) were injected with vehicle. Mink were sacrificed 24 hr after injection and levels of PRL, E2, P4, ER, and PR determined. Bromocriptine suppressed serum concentrations of PRL (P < 0.001), increased serum levels of E2 (P < 0.05) and levels of PR (P < 0.01), but had no effect on levels of P4, uterine weight, glucose oxidation, DNA and protein synthesis, or concentrations of ER.(ABSTRACT TRUNCATED AT 250 WORDS)