Temporal concentrations of rat placental lactogen in the peripheral circulation

Placental lactogen (PL) is an abundant placental protein identified in several species, but to date little is known of mode or control of PL secretion. In the present study we sought to define the minute-to-minute variation in rat PL (rPL) secretion in late pregnancy by repeated blood sampling over a 3-h period. The results indicate that rPL may be secreted in an episodic pulsatile manner similar to the pulsatile secretion of pituitary prolactin (Prl) and growth hormone (GH). This evidence suggests a highly regulated dynamic control of secretion of a placental hormone.