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Male rat hepatocyte cultures have been obtained. The culturing hepatocytes had a stable level of some morphological and functional properties. A high level of estrogen receptors (ER) and E2-sensitive unusual estrogen-binding protein (UEBP) was found. A direct dose-dependent inhibiting effect of physiological (10(-10)-10(-7) M) concentrations of E2 on UEBP content was established in cell cultures incubated with the hormone for 3 days. Hexestrol (but not cholesterol) was found to exert a direct inhibiting effect. The inhibiting effect of E2 (10(-9) M) was observed after a 24 hour incubation of hepatocytes with the hormone but was less pronounced. In this case a significant increase in UEBP concentration in hepatocytes was noted 72 hours after the removal of E2. It is concluded that physiological concentrations of E2 can exert a direct regulatory influence on certain functions of culturing hepatocytes acting via hepatocyte ER.