Altered Balance between Thyrotropin-Releasing Hormone and Dopamine in Prolactinomas and Other Pituitary Tumors Compared to Normal Pituitaries

We measured TRH and dopamine (DA) concentrations in prolactinomas and other pituitary tumors in order to further understand the roles of these two factors in the hormone hypersecretion and growth of these tumors. The mean TRH concentration (by RIA) in 16 prolactinomas was 247 +/- 92 (+/- SE) fmol/mg cell protein (range, 10-1297), near that found in normal pituitary tissue. The prolactinoma TRH content did not correlate with the patient's tumor size or plasma PRL level. By contrast, DA assayed by high pressure liquid chromatography was present in normal pituitary tissue (7.3 +/- 3.5 pmol/mg cell protein), but was very low or undetectable in the prolactinomas (23 fmol/mg cell protein or less). 3,4-Dihydroxyphenylacetic acid, also assayed by high pressure liquid chromatography, was undetectable in both normal pituitary tissue and prolactinomas. This imbalance between TRH and DA content also was found in GH-secreting and nonsecreting adenomas. The TRH content in 18 GH-secreting tumors (24 +/- 6 fmol/mg) was considerably lower than that in the prolactinomas (P less than 0.001). In 8 nonsecreting adenomas, the mean TRH concentration was 109 +/- 28 fmol/mg, about half of that in the prolactinomas. In those 2 types of adenomas, DA also was nearly undetectable (less than or equal to 73 fmol/mg cell protein). We conclude that the imbalance between TRH and DA contents in prolactinomas compared to those in normal pituitary tissue might participate in the mechanisms leading to hypersecretion of PRL and the growth of all types of pituitary adenomas.