Serum prolactin levels in the control group, composed of saline-treated and untreated mink, increased gradually through gestation from 14.15 ± 3.9 ng/ml during diapause (March 19) to 54.08 ± 7.6 ng/ml during postimplantation gestation (April 15, Fig. 1B). Delivery of 2 mg of bromocriptine per day by minipump reduced prolactin levels to below pretreatment values within 2 days of insertion of the pumps, and prolactin remained below control levels through the duration of the treatment (March 31, Fig. 1B, p < 0.05). Embryo implantation, as indicated by the occurrence of uterine swellings, was observed as early as March 31 in a few control animals. buy cipro
Most control animals of 15 ng/ml, but a substantial 5-fold increase thereafter (Fig. 3). Suppression of endogenous prolactin levels with bromocriptine prevented the increase in the abundance of ovarian prolactin receptor mRNA (Fig. 2, A and C, p < 0.05). Radiolabeled prolactin binding to homogenates of whole ovaries followed the pattern of expression of prolactin receptor mRNA (Fig. 4), and no statistically detectable differences were present between March 19 and 29. Binding increased between March 29 and April 15 (p < 0.05). Prolactin receptor mRNA abundance and prolactin binding to ovarian homogenates were correlated (r = 0.51, p < 0.01), and both were correlated to serum prolactin levels (r = 0.45 and r = 0.48, respectively, p < 0.02). The abundance of LH receptor mRNA in whole ovaries was greater on March 21 and 23 relative to March 19 and 27 (Fig. 5, A and B, p < 0.05).
FIG. 1. A) Mean ± SEM of mink serum progesterone levels from embryonic diapause through early-postimplantation gestation in untreated animals (control) or those bearing Alzet minipumps releasing 2 mg/day bromocriptine. B) Mean ± SEM of mink prolactin concentrations in the same samples. A and B, n = 3 animals per sampling date.
FIG. 2. A) Mean ± SEM of prolactin receptor mRNA abundance in ovarian tissue collected from pregnant mink at 3-day intervals (n = 3 per sampling date) between March 19 and March 31 and every 5 days thereafter until April 15. B) The upper panel is a representative control Northern blot hybridized with the mink prolactin receptor probe, and the lower panel is the same control Northern blot rehybridized with a ribosomal 28S probe. C) The upper panel displays representative Northern blot of bromocriptine-treated animals. The blot was hybridized with the mink prolactin receptor probe, while the lower panel is the same blot rehybridized with a human ribosomal 28S probe.
FIG. 3. Relative abundance of prolactin and LH receptor transcripts in pools of CL from 10 or more ovaries taken from mink in embryonic diapause (March 21), at the approximate time of luteal activation (March 25), and at the postimplantation (April 9) stage of gestation. Results are expressed as the dimensionless ratio of the density of the sum of the three major bands of the prolactin receptor mRNA and the single band of the LH receptor mRNA divided by the corresponding densitometric value for the 28S ribosomal RNA.