Mammotrophic activity in rat amniotic fluid.

Mammotrophic activity was present in rat amniotic fluid collected on days 13, 15 and 19 of pregnancy. The mammotrophic activity in the fluid was equivalent to that in the maternal serum on day 15, but is was lower on day 19. The effect of tha amniotic fluid was similar to that of human placental lactogen on the rat mammary gland in vitro. The prolactin concentration in the amniotic fluid was low (approximately 1 ng/ml).