Proposed mechanism of functional suppression of a prolactinoma by a dopamine-secreting paraganglioma. Dopamine is secreted from the paraganglioma into the systemic circulation, leading to increased dopamine concentration in the hypophyseal portal system. Increased dopamine binding to the dopamine D2 receptor inhibits prolactin secretion from the prolactinoma. Removal of the source of excess dopamine via paraganglioma resection results in disinhibition of prolactin secretion. The prolactin remains elevated from continued secretion from the prolactinoma. Functional dopamine withdrawal may also cause transient (<60 minutes) hyperprolactinemia in the absence of prolactinoma. Created in BioRender.