The properties of prolactin secretion in patients with prolactin secreting pituitary adenomas

Plasma prolactin (PRL) responses to several exogenous agents are variable in patients with prolactinomas. In this study the factors determining the responsiveness to exogenous stimuli were investigated in 35 patients with prolactinomas. Among these patients, 14 patients were responder (greater than 150% increase of basal value) to TRH, sulpiride (DA D2-receptor blocker) and arginine, and remaining 21 were non-responder to these three agents. Plasma TSH responses to sulpiride, an indirect indicator of hypothalamic dopaminergic tone on pituitary gland, were similar between responder (delta TSH: M +/- SEM; 5.3 +/- 0.2 microU/ml) and non-responder (delta TSH: 5.6 +/- 0.2 microU/ml), and were greater than those in normal subjects (delta TSH: 0.7 +/- 0.2 microU/ml, n = 18) (P less than 0.001). The plasma PRL responses to dopaminergic agents (L-dopa, CB-154, dopamine) were greater in responders than in non-responders (% of basal: L-dopa, 33.7 +/- 3.7% vs 51.6 +/- 5.6% at 150 min, P less than 0.05; CB-154, 16.5 +/- 2.6% vs 30.9 +/- 2.8% at 6 hr, P less than 0.05; dopamine, 31.7 +/- 5.6% vs 44.9 +/- 4.3% at 90 min, P less than 0.05). When all patients were divided into microadenoma (n = 12) and macroadenoma patients (n = 23), there were no differences in plasma PRL responses to these agents between the two groups. Again, there were no differences in the duration of illness between the responder and non-responder patients (61.9 +/- 13.7 vs 54.1 +/- 12.0 months). During the short term CB-154 treatment (7.5mg/day for 3 approximately 5 weeks) in 8 responders and 15 non-responders, all responder patients showed normalization of plasma PRL levels, while such normalization was observed in only 6 non-responder patients. These results suggest that in prolactinoma patients variable responsiveness to several exogenous agents are depending on the sensitivity to several exogenous agents are depending on the sensitivity of prolactinoma itself, regardless of the endogenous hypothalamic dopaminergic tone, tumor size or duration of the illness.