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 r eceptors in the oviduct of ovariectomized gilts at various times after admi nistration of oestradiol benzoate (10 mu g kg(-1) body weight) to determine whether LH participates in the regulation of oviductal contractions. Polyc lonal antibodies to the LH receptor were used in immunocytochemical and wes tern blot analyses of oviductal tissues. The mechanical activity of the ist hmus 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 li ttle competition for receptor occupancy between hCG and pig FSH, bovine thy roid-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 inhi bit the binding of [I-125]hCG. Oestradiol benzoate increased (P < 0.01) the number of LH binding sites in oviduct 24, 48 and 72 h (0.60 +/- 0.08, 1.62 +/- 0.15, 2.48 +/- 0.35 fmol mg(-1) protein; n = 4 per treatment, respecti vely) after injection compared with the control gilts treated with corn oil (0.20 +/- 0.04 fmol mg(-1) protein; n = 4). The affinity of oviductal LH/h CG binding sites (K-a) varied from 4.0 to 8.5 x 10(10) l mol(-1) and was si milar to that of luteal cell binding sites (6.1 x 10(10) l mol(-1)). Oestra diol benzoate also resulted in more intense LH receptor immunostaining of t he tubal mucosal epithelium, smooth muscle cells and blood vessels as compa red with controls. Western blotting has revealed that the pig oviduct, simi lar to the corpus luteum, contains 75, 48 and. 45 kDa immunoreactive LH rec eptor proteins. Treatment with LH in vitro (100 ng ml(-1)) affected the con tractility of oviduct. During the peri-ovulatory stage of the oestrous cycl e,the amplitude, frequency and area under curve(s) of the isthmus decreased (P < 0.05), as did the frequency and area under curve (P < 0.05 and P < 0. 01, respectively) of the ampulla (n = 4). The frequency and area under curv e of the oviductal contractions were also significantly reduced during the early follicular phase of the oestrous cycle (P < 0.05). There was no effec t of LH (or hCG) on the frequency and area under curve of the oviductal con tractions during luteal stages of the oestrous cycle (n = 8). These data in dicate that (1) the pig oviduct possesses immunoreactive and functional LH receptor, (2) oestradiol promotes the synthesis of LH receptor in the epith elium and smooth muscles, and (3) LH causes the relaxation of oviduct, espe cially during the peri-ovulatory stage of the oestrous cycle. In summary, t he results of the present study indicate that LH can control oviductal cont ractions directly and may be partially responsible for the relaxation of is thmus during fertilization in pigs.