Evidence of abnormal dopaminergic control of prolactin in patients with hypothalamic and pituitary tumors.

Prolactin secretion was investigated in an attempt to identify the patterns of responses in different types of tumors. Forty four patients were studied: thirty patients with prolactinomas (Group 2); nine patients with growth-hormone (GH)-adrenocorticotropic hormone (ACTH)-secreting pituitary tumors and hypothalamic tumors (Group 3); and five patients with non-secreting pituitary tumors (Group 4). A control group (Group 1) consisted of 60 healthy subjects (30 males and 30 females). All were submitted to testing by nomifensine (Nom), domperidone (Dom) and thyrotropin releasing hormone (TRH). The prolactin levels were measured by radioimmunoassay (RIA). In group 2 the suppression of PRL with Nom and the stimulation with Dom and TRH were significantly lower than in the control group (p less than 0.001). There was no statistically significant difference between groups 2 and 3 in the suppression with Nom. The increase with Dom in group 3 was significantly greater than that in group 2 (p less than 0.001) and less than that in the control group (p less than 0.005). The rise in PRL with TRH was also significantly higher in group 3 than in group 2 (p less than 0.001) and similar to that of the control group. Group 4 gave the same results as the control group to all 3 tests. Our results indicate a dopaminergic irregularity in the hypothalamic and GH-ACTH-secreting pituitary tumors, thus supporting a hypothalamic etiopathogenesis of these tumors. The normality of the GH-ACTH-secreting pituitary tumors and hypothalamic tumor responses to TRH is one more factor in differentiating these from prolactinomas. The normal response of the non-secreting tumors may involve a primary pituitary etiology of these tumors.