Normal lactotroph sensitivity to graded low-dose dopamine infusions in pathological hyperprolactinemia

The question as to whether there is lactotroph resistance to dopamine (DA) in pathological hyperprolactinemia (PHP) is unresolved. Previous studies utilizing low-dose DA infusions to study lactotroph function have not considered the diurnal changes in prolactin (PRL) secretion that occur in normals but which are lost in PHP. As PRL levels show a fall in the hours after waking, studies performed during this time of day will falsely show a greater fall of PRL in normals than in PHP patients. The aim was to readdress the issue of lactotroph sensitivity using a study designed to minimize the problem arising from diurnal PRL changes. Eight normal subjects, 17 patients with PHP, and 6 hyperprolactinemic patients with nonfunctioning pituitary tumors (NFTs) were studied with three graded doses of DA - (0.01, 0.05, and 0.5 micrograms/kg X min) - by relating the changes induced by each dose to the maximal spontaneous fall in PRL that occurred during a 3-hour control saline study. The mean +/- SE maximal fall in PRL during control saline infusion to 46.0 +/- 4.1% of basal in normal subjects was significantly greater (p less than 0.001) than the fall in patients with PHP (88.0 +/- 1.0%) or NFTs (87.5 +/- 2.6%). The apparent fall in PRL was significantly greater in normals during the two lower infusion doses, but not at the highest dose.(ABSTRACT TRUNCATED AT 250 WORDS)