Estrogen Action in Vitro

Abstract

Abstract Physiological concentrations of estradiol added in vitro to immature rat uteri in Eagle's HeLa medium induced the near maximal (compared to in vivo) synthesis of a specific uterine protein (induced protein (IP)). The magnitude of IP induction closely corresponded to the amount of nuclear bound [3H]estradiol at different estradiol concentrations. Maximal IP induction and maximal binding of [3H]estradiol to nuclear receptor were obtained with 2 to 3 x 10-8 m estradiol; 2 to 3 x 10-9 m estradiol gave a 50% response with both; and at 10-10 m, induction and binding were minimal. The greatest in vitro response at 2 x 10-8 m estradiol was about 85% of that obtained in vivo. The coincidence of the induced proteins synthesized after either in vivo or in vitro hormone administration was shown by coelectrophoresis on polyacrylamide gels. Likewise, the over-all pattern of newly synthesized soluble proteins was the same in uteri stimulated with estrogen either in vitro or in vivo. The time course of the rate of IP synthesis (a measure of amount of IP-synthesizing capacity) in vitro (detectable by 15 min; 50% by 20 to 30 min) was similar to that obtained in vivo. In both situations, the increase in IP-synthesizing capacity is actinomycin D sensitive. Also, the rate of accumulation of IP-synthesizing capacity is highest initially and falls off rapidly with time (by 30 min) whether accumulation occurs in vitro or in vivo; at this time, however, the amount of estradiol is continuing to increase or remains at a high level in the nucleus. Induction of IP synthesis shows a strict hormonal specificity. Only estrogenic compounds induced, whereas progesterone, testosterone, and insulin did not. The efficacy of induction was 17 β-estradiol g diethylstilbestrol g estriol g 17 α-estradiol. Cyclic adenosine 3',5'-monophosphate and N6, O2'-dibutyryl cyclic adenosine 3',5'-monophosphate, at 10-3 or 10-5 m, did not induce IP and neither enhanced nor diminished the induction of IP due to estradiol. These findings clearly indicate that estrogen can directly stimulate the uterus without the requirements of intact vascular or nervous systems.