Synthesis and release of human placental proteins and HPL were examined in 6 normal term placentas incubated with 3H-l-leucine in vitro for up to 96-120 hr. The HPL content in fresh tissues was approximately 300 μg/g wet weight. The amount of proteins and 3H-proteins released into the medium was fairly constant among different placentas, while a variable release of HPL was noted in different placentas. The per cent of 3H-HPL to 3H-proteins in medium (5-10% in 4 placentas) was significantly higher than that in tissue (1-2%), indicating preferential or selective release of HPL. Two placentas showed an extremely high incorporation rate of 3H-leucine into HPL, suggesting the possible existence of a biochemically abnormal placenta. Over 80% of the total synthesized 3H-HPL was released into the medium within the first 24 hr incubation, while only 22 % of the total 3H-proteins was released in this period, suggesting a rapid rate of release of HPL. The specific activity of 3H-HPL in medium was much higher when compared with that in tissue, while the ratio of specific activity of 3H-proteins in medium to that in tissue was unity after a 24-48 hr incubation period. This result implies that there may be a stable tissue pool of HPL which is not as readilyreleased as newly synthesized 3HHPL. A hypothetical scheme for the dynamic aspectsof the biosynthesis and release of HPL is presented. (Endocrinology85: 1037, 1969)
No takes yet. Share an insight, caveat, or question.
Suwa et al. (1969) studied this question.