Effect of Estrogen Administration in vivo on Prolactin Release by Rat Pituitary in vitro. ∗,†

Summary

Twenty-seven mature female rats were injected daily with 50 μg of estradiol benzoate in oil for 6 days, while 27 controls received only oil injections. On the seventh day the pituitaries were removed and cut into halves. Three anterior pituitaries from the estrogen-treated rats and 3 from the controls were placed in separate flasks (9 pairs of flasks) containing 2 cc of synthetic medium “199,” and incubated for 2 hours in a Dubnoff metabolic shaker at 37°C in an atmosphere of 95% O₂-5% CO₂. After incubation the medium from each flask was assayed for prolactin. The pituitaries from the estradiol benzoate-treated rats released 96% more prolactin into the medium than the pituitaries from control rats on a per pituitary basis, and 47% more on a 100 mg pituitary weight basis. Administration of estradiol benzoate increased the average weight of the anterior pituitaries by 45% and the average pituitary prolactin content by 187%. These results demonstrate that administration of estradiol benzoate in vivo increases the capacity of the anterior pituitary to release prolactin in vitro.