Evidence for the presence of luteinizing hormone-chorionic gonadotrophin receptors in the pig umbilical cord

Pig umbilical cord, like that of humans, contains two arteries and a vein s urrounded by Wharton's jelly with amnion covering the exterior surface. The aim of the present study was to investigate whether LH-hCG receptors are p resent in the pig umbilical cord, using Light microscope immunohistochemist ry, semiquantitative autoradiography, western blotting and reverse transcri ption-polymerase chain reaction. Umbilical cords were collected on days 48, 71 and 103 of fetal life (n = 6). Monoclonal and polyclonal anti-LH recept or antibodies were used to study receptor distribution. Immunoreactivity wa s observed in the umbilical blood vessels, the epithelium of umbilical amni on and cells in the Wharton's jelly. No differences in LH-hCG receptor dist ribution related to the sex of the fetus, period of fetal life or section o f the umbilical cord were observed. Strong immunostaining was observed in u mbilical vein and in umbilical arteries. However, in the arteries, the tuni ca media expressed weaker receptor immunostaining than did the tunica intim a and tunica adventitia. No immunoactivity was detected in non-target tissu e (skeletal muscle) but LH receptors were immunostained in the pig ovary. T opical autoradiography showed that vein and arteries in the umbilical cord bind I-125-labelled hCG, which was highly diminished after co-incubation wi th an excess of unlabelled hCG. The binding of I-125-labelled hCG to the Wh arton's jelly and epithelial amnion was less intense than it was to vessels . Gonadotrophin binding sites were not present in the skeletal muscle. The pig umbilical arteries, vein and Wharton's jelly contained a 75 kDa immunor eactive LH-hCG receptor protein similar to that found in corpora lutes. Sou thern blot analysis of reverse transcription-polymerase chain reaction prod ucts, performed to enhance the sensitivity and specificity of LH receptor t ranscripts determination in umbilical cord tissues, revealed that the expec ted fragments of 740 and 470 bp were present in the arteries, vein, Wharton 's jelly and corpora lutea (positive control). An additional product of 670 bp was found in the corpora lutea and arteries of umbilical cord, but not in the vein and Wharton's jelly. This is probably the first reported eviden ce of the presence of LH-hCG receptors in the umbilical cord of a non-human female mammal.