The Luteotropic Activity of Rat Placenta Is Not Due to a Chorionic Gonadotropin*

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Abstract
Placentae or uteri form pregnant rats (days 12-21) contained no detectable .alpha.-subunit of the glycoprotein hormones (chorionic gonadotropin, TSH, FSH and lutropin) when assyaed in either a rat or human .alpha. radioimmunoassay. The heads of rat fetuses contained increasing concentrations of .alpha.-subunit when asayed from days 12-20 of gestation (7.2-46 ng/g). Human term placenta contained large quantities of .alpha.-subunit (16,000 ng/g). .alpha.-Subunit was synthesized by the cell-free translation of poly(A)-enriched mRNA from mouse TSH-secreting pituitary tumor and human term placenta but not from rat placentae or uterine implantation sites (days 11-21 of gestation). In addition, .alpha. mRNA was detected in mouse TSH-secreting pituitary tumor, rat pituitary, and human term placenta by hybridization to a 32P-labeled mosue .alpha. complementary DNA probe although and .alpha. mRNA could be detected in rat placentae (days 13-21 of gestation). The luteotropic activity found in pregnant rodents must be caused by a substance with a structure substantially distinct from any known gonadotropin.