Utility of<scp>l</scp>-dopa and Water Loading in Evaluation of Hyperprolactinemia

Abstract

Basal serum prolactin concentration was determined by radioimmunoassay in normal male and female subjects and patients with functional galactorrhea and pituitary tumors. Mean serum prolactin concentration was 34 ± 25.5 (1 sd) ng/ml for normal males, 45 ± 31.5 ng/ml for normal females, 96 ± 73.5 ng/ml for functional galactorrhea patients, and 12,444 ng/ml for pituitary tumor patients. There was considerable overlap in the serum prolactin levels of functional galactorrhea patients with levels found in normal females. Likewise, basal serum prolactin concentration in 2 of 8 patients with pituitary tumors was not clearly higher than some patients in the functional galactorrhea group. In order clinically to separate patients with pituitary tumors from patients with other causes of hyperprolactinemia, we administered l-dopa and a water load to individuals in each group. l-dopa resulted in greater than 50% suppression of serum prolactin concentration in all normal subjects and all patients with functional galactorrhea. Three of five patients with pituitary tumors suppressed to less than 50% of the baseline value, a response similar to that seen in normal subjects and patients with functional galactorrhea. Following oral water loading, all normal subjects and functional galactorrhea patients responded with suppression of serum prolactin to less than 50% of baseline. None of the patients with pituitary tumors, however, showed significant suppression of serum prolactin concentration following water loading. Thus, in contrast to the prolactin response to l-dopa, the response to water loading did appear to separate patients with pituitary tumors from those with functional disorders of prolactin secretion.