The distribution of placental lactogen in the human term placenta

Serial frozen sections of human term placentae were examined by quantitative morphology and, after extraction, by a radioimmunoassay for human placental lactogen (HPL). The total quantity of HPL in the placenta was estimated as 720 mg. The amount of HPL was related to the amount of trophoblast in any area, but otherwise did not vary in different parts of the placenta. A semi-logarithmic relationship was observed between the amount of HPL and the percentage trophoblast in a section. It is suggested that the amount of HPL in a given area of the placenta is related to the blood-flow in that area.