Placental luteinizing hormone-releasing factor and its synthesis.

The synthesis of a placental luteinizing hormone-releasing factor (pLRF), which is immunologically, physiochemically, and biologically indistinguishable from synthetic LRF, was demonstrated. The incorporation of 3H-labeled leucine by human placental tissue in vitro into pLRF was determined by purification on carboxymethyl-cellulose and specific immunoprecipitation of the 3H-labeled pLRF. The specific activity of the pLRF released into the medium increased 100-fold from day 1 to day 2 of culture and attained a concentration of 2.84 microcuries per microgram. These data indicate that the pLRF that was released initially was endogenous, whereas that released subsequently reflected synthesis.