Secretion of human chorionic gonadotrophin by the early placenta in Vitro.

The secretion in vitro of HCG and proteins was studied in fragments of placenta from women in the first trimester of pregnancy by a pulse-chase system. A 10-min pulse with [3H]leucine was used. It was concluded that the approximate half-time of release of HCG was 150 min. Proteins precipitable with trichloroacetic acid had a bi-exponential pattern, the half-times of release being 100 and 270 min. These rates of release indicate that the HCG produced by the early placenta was rapidly passed into the circulation rather than stored.