Effect of estradiol and progesterone on oviductal LH-receptors and LH-dependent relaxation of the porcine oviduct

We have previously shown that the porcine oviduct possesses immunoreactive and functional LH receptors and that LH causes relaxation of the oviduct, e specially during the periovulatory stage of estrous cycle. The current stud ies were undertaken to investigate the effects of estradiol and progesteron e on LH receptor protein and LH-stimulated motility of the oviduct in stero id-primed ovariectomized gilts. Twenty-one cross-bred gilts were ovariectom ized at 6 mo of age. Four weeks later gilts received daily intramuscular in jection of either 2 mt corn oil (control n=4), estradiol benzoate (EB) 1.5 mg (n=6), progesterone 50 mg (n=5), or 1.5 mg EB plus 50 mg progesterone (n =6) for 4 consecutive days. The gilts were slaughtered on Day 5 after the f irst injection of steroids or vehicle. Rings of isthmus and ampulla were co llected from each oviduct and placed in a tissue chamber perfused with Kreb 's solution for 60 min. The mechanical activity was recorded for 30 min aft er LH treatment. Immunoreactivity of LHR rn the Fallopian tube sections wer e detected in the epithelium of the tubal mucosa, smooth muscle cells and t he blood vessel endothelium. Western blotting showed that porcine oviducts contain 75, 48 and 45 kDa immunoreactive LH receptor proteins, like the cor pus luteum (CL). The lowest receptor expression was found in controls and i n gills treated with estradiol or progesterone. Combined treatment with est radiol and progesterone resulted in a significant increase of LH receptor p rotein concentrations when compared with control animals. In vitro LH treat ment affected oviduct contractility of combined estradiol and progesterone treated gilts but not the oviduct of the remaining groups. It also caused a decrease in amplitude, frequency and areas under the curve (AUC) of ampull a (P<0.05) and the amplitude and AUC of isthmus (P<0.001) in combined estra diol and progesterone-primed gilts. These results indicate that estradiol a nd progesterone together, but not separately, increase LH receptor protein in the porcine oviduct and thar combined estradiol and progesterone priming is necessary for LH-induced relaxation of the porcine oviduct. (C) 2000 by Elsevier Science Inc.