Oestrogen-dependent expression of LH/hCG receptors in pig Fallopian tube and their role in relaxation of the oviduct

The current studies investigated the concentration and distribution of LH receptors in the oviduct of ovariectomized gilts at various times after administration of oestradiol benzoate (10 \g=m\gkg\m=-\1body weight) to determine whether LH participates in the regulation of oviductal contractions. Polyclonal antibodies to the LH receptor were used in immunocytochemical and western blot analyses of oviductal tissues. The mechanical activity of the isthmus and ampullar segments of oviduct, collected from 16 cyclic gilts, was recorded for 30 min after LH or hCG treatment. In the oviduct, there was little competition for receptor occupancy between hCG and pig FSH, bovine thyroid-stimulating hormone (TSH), pig growth hormone (GH) and pig prolactin (1.2, 0.1,0.01 and < 0.001%, respectively) but pig LH could completely inhibit the binding of[125I]hCG. Oestradiol benzoate increased (P < 0.01) the number of LH binding sites in oviduct 24, 48 and 72 h (0.60 \m=+-\0.08,1.62 \m=+-\0.15, 2.48 \m=+-\0.35 fmol mg\m=-\1protein; n = 4 per treatment, respectively) after injection compared with the control gilts treated with corn oil (0.20 \m=+-\0.04 fmol mg\m=-\1protein; n = 4). The affinity of oviductal LH/hCG binding sites(Ka) varied from 4.0 to 8.5 \m=x\1010l mol\m=-\1 and was similar to that of luteal cell binding sites (6.1 \m=x\1010l mol\m=-\1).Oestradiol benzoate also resulted in more intense LH receptor immunostaining of the tubal mucosal epithelium, smooth muscle cells and bloo