The effect of estriol on the production of alpha-fetoprotein by the liver in adult mice.

A single intraperitoneal injection with a 10 mg estriol (E3) in aqueous suspension induced a large and prolonged elevation of serum alpha-fetoprotein (AFP) in adult mice. E3 also raised the mitotic activity of hepatocytes in the absence of liver injury. Although both the AFP concentration and hepatocyte proliferation reached the peak on day 5 after E3 administration, a high level (about 12,500 ng/ml) of serum AFP persisted for a long period after hepatocyte proliferation declined. Five mg E3 showed a remarkable threshold effect on AFP elevation and 3 mg E3 on hepatocyte proliferation. Immunohistochemical studies indicated AFP production by hepatocytes in adult mice after the E3 administration.