The Influence of Estrogen on Pituitary Growth and on Prolactin Production in Vitro in the Diabetic Rat

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Abstract
The influence of estrogen injection on anterior pituitary (AP) weight and on prolactin secretion in vivo and in vitro was examined in the diabetic rat. In the absence of insulin estrogen did not have any effect on increasing AP weight while the increase in uterine weight was similar to that of normal animals. Thus insulin is an obligatory permissive mitogenic agent for estrogen-induced pituitary growth. The lack of insulin had no effect on the estrogen-induced increase in prolactin production. However, the method of expressing prolactin production is significant to the interpretation. If the prolactin production is expressed on the basis of AP weight then erroneous conclusions can result, i.e., an increase in prolactin release. Only when prolactin production is expressed on a pituitary basis does the in vitro finding agree with the in vivo observation. Data are also presented under a number of experimental circumstances to indicate that the amount of prolactin released into the medium is a percentage (approximately 20-25%) of that present in the pituitary, and that estrogen influences the capacity of the pituitary to secrete prolactin in vitro in addition to an effect on the release mechanism in vivo.