Hyperprolactinemia in clinically asymptomatic, fertile men: report of two cases

Although the role of prolactin (PRL) in men is undefined, hyperprolactinemia has been associated with decreased reproductive potential. Two healthy, fertile, asymptomatic men with hyperprolactinemia are reported. Both men had normal puberty. Both were euthyroid and had normal gonadotropin levels and androgen profiles. Semen analyses were normal and both had fathered children. The serum PRL level (mean +/- standard error of the mean) (N = 5) of subject 1 was 48 +/- 12 ng/mL, and of subject 2 was 214 +/- 5 ng/mL. Sella turcica computed tomography scans with contrast were normal. The two subjects underwent a thyrotropin-releasing hormone stimulation test. Serum PRL and TSH were measured by radioimmunoassay. At time 0 and at 15 minutes, PRL bioactivity was measured in the Nb2 node rat lymphoma assay. Both subjects showed a normal TSH response to thyrotropin-releasing hormone. Subject 1 had baseline PRL immunoactivity and bioactivity measuring 41 and 50 ng/mL, respectively, peaking at 76 and 70 ng/mL 15 minutes after infusion of thyrotropin-releasing hormone. Subject 2 had baseline PRL immunoactivity of 200 ng/mL and bioactivity of 67 ng/mL, neither of which were altered by infusion of thyrotropin-releasing hormone. Administration of L-dopa decreased the serum PRL of subject 1 from 33 to 7 ng/mL, but had no clinically significant effect in subject 2. Prolactin and gonadotropin secretion may be dissociated in men so that hyperprolactinemia may not always manifest as reproductive dysfunction.