Concentrations of nuclear progesterone receptors in endometrium of virgin and repeat breeder heifers after embryo transfer.

The present study aimed to correlate the repeat breeder syndrome in the bovine with an impaired or suboptimal uterine progestational response. Concentrations of nuclear (i.e. transformed) receptors for progesterone (PRn) were determined with a binding and exchange method in endometrial samples from virgin (VH) and repeat breeder (RBH) heifers 15 days post oestrus. The heifers were recipients of Day 7 demi-embryos collected from donors with normal fertility and transferred 8 days prior to tissue sampling. Results were compared with both the type of heifer, the condition of the embryo present within the uterus and the temporal relationship to the hormone plasma levels. The binding data for PRn indicated that a single class of high-affinity, low-capacity sites existed. The amount of PRn in VH endometria holding embryonic structures was significantly greater than in RBH, but no statistical differences were found in their plasma progesterone levels. PRn concentrations were also higher in the uterine horn in which an elongated (greater than 15 mm), morphologically normal embryo was present, when compared to cornua with small (less than 5 mm) embryos, regardless of recipient group. Furthermore, in endometria with an elongated embryo in the lumen, the relative amount of PRn was significantly greater in VH than in RBH. The present results indicate that the RBH recipients of Day 7 demi-embryos by Day 15 have fewer numbers of specific receptors for maternal progesterone, which could explain in part the poorer development of the transferred embryos compared with that in virgin heifers.

Evidence for the presence of luteinizing hormone/human chorionic gonadotropin-binding sites in the porcine uterus.

LH/hCG-binding sites were measured in crude membrane fractions of porcine uteri. Specific high affinity and low capacity receptors for LH/hCG were found in all (n = 17) membrane preparations of myometrium but in only 5 of 17 crude membrane fractions of endometrium of porcine uteri. There was very little competition between hCG and porcine GH (pGH), bovine TSH, pFSH, and pPRL (0.5%, 0.3%, 0.2%, and less than 0.005%, respectively). Specificity of [125I]hCG binding to other tissues was determined by incubating crude membrane preparations of heart, skeletal muscle, liver, and kidney. Numbers and affinities of available LH/hCG-binding sites were characterized in all samples of myometrium and 5 endometrium membrane preparations that were positive for LH/hCG receptors. The results indicate that the number of uterine LH-binding sites in myometrium (0.66 +/- 0.17 fmol/mg) is 10 times less than the receptor capacity in porcine corpora lutea (7.46 +/- 0.54 fmol/mg) when expressed per mg protein of crude membrane preparation. However, it is approximately 60 times less when expressed per mg DNA equivalent of initial homogenate (1.31 +/- 0.28 vs. 81.18 +/- 3.64 fmol/mg, respectively). Receptor affinities of uterine LH/hCG-binding sites remained comparable to those of corpora lutea receptors (Ka = 7.8 X 10(10) M-1). Concentrations of LH/hCG-binding sites in myometrium taken from gilts in the late follicular phase of the estrous cycle (0.13 +/- 0.06 fmol/mg protein; n = 5) were significantly less (P less than 0.05 and P less than 0.01) compared to those in myometrium from luteal phase (0.85 +/- 0.22 fmol/mg protein; n = 6) or early pregnancy (1.03 +/- 0.15 fmol/mg protein; n = 6), respectively. This is probably the first evidence demonstrating specific binding of [125I]hCG by LH receptors in female uterine tissue.