Prolactin Response to Arginine in Normal Subjects and in Patients with Hyperthyroidism

Abstract

The effect of arginine on serum prolactin concentrations was studied in 18 normal subjects and in 7 patients with hyperthyroidism. In normal subjects, arginine infusion produced an increase of serum prolactin at least 6 ng/ml from the baseline, and the mean peak level (25.2 ± 3.3 ng/ml, mean ± se) was significantly higher than the basal level (8.6 ± 5.2 ng/ml, P < 0.001). There was no significant difference in the peak levels between sexes. Unlike prolactin, concomitant serum thyrotropin levels did not change after the arginine infusion. In hyperthyroid patients, the increment of serum prolactin after arginine infusion at 30 min (3.9 ± 1.5 ng/ml) was significantly lower than that of the normal controls which were matched by age and sex (17.1 ± 4.4 ng/ml, P < 0.05). After treatment when these patients were euthyroid, the increment of prolactin after arginine infusion at 30 min was significantly increased (16.3 ± 4.3 ng/ml, P < 0.05) and had reached the level of the control subjects. These data indicate that the prolactin response to arginine in hyperthyroidism is diminished.