Estrogen is the most important stimulator of prolactin synthesis and release. This affect is clearly observed in the third trimester where a pregnant female experiences the development of ductal and lobular system in breasts. Estrogen increases the release of prolactin by two ways. First, it enhances the growth of prolactin-releasing cells. Secondly, it inhibits the release and function of dopamine. Dopamine inhibits the release of prolactin. When estrogen inhibits Dopamine, more prolactin is released.