Growth hormone responses to L-dopa in depressed patients.

Plasma human growth hormone responses to oral administration of 500 milligrams of L-dopa were analyzed in three groups of subjects: normals, age 20 to 32; normals, age 48 to 68; and unipolar depressed patients, age 45 to 68. While only 7 percent of the young normals had deficient human growth hormone responses to this stimulus, 36 percent of the older normals and 77 percent of the depressed patients failed to have adequate responses, suggesting an effect of age and a further effect of depressive illness. Because the release of human growth hormone appears to be closely related to brain catecholamine metabolism, the deficient responses in the depressed patients may provide further support to the concept of a neurochemical defect in depressive illness.