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No difference between micro- and macroprolactinomas in the prolactin responsiveness to metoclopramide and dopamine
1Second Chair of Endocrinology, University of Milan, Ospedale S. Luca IRCCS, Milan, Italy.
Abstract:
Differences between micro- and macroprolactinomas, as regards the prolactin secretory pattern in response to pharmacological challenges, have been reported in in vivo and in vitro models, and interpreted as being due to different dopaminergic regulation of prolactin release. In 32 patients with prolactin-secreting tumors, 19 with microprolactinomas and 13 with macroprolactinomas, and ten healthy volunteers, we evaluated the prolactin secretion in response to pharmacological manipulations of central dopaminergic tone. To this end, three tests were performed, in random order: (1) 4-h saline infusion; (2) 10 mg metoclopramide as i.v. bolus; (3) 4-h dopamine infusion (0.01 microgram/kg/min) with a 10-mg metoclopramide bolus given after the second hour of infusion. Dopamine infusion, compared to saline, caused a significant prolactin decrease in all the three groups of subjects, without significant difference between micro- and macroprolactinoma patients. In prolactinoma patients, administration of metoclopramide induced a significant rise in plasma prolactin which, however, was significantly lower than the one displayed by controls. Again, no difference was observed between the two groups of hyperprolactinemic patients. Dopamine infusion induced a significant and comparable increase in the prolactin response to metoclopramide in micro- and macroprolactinoma patients, while it was ineffective in control subjects. In conclusion, no differences appear to exist between micro- and macroprolactinoma patients as regards the prolactin secretory pattern during pharmacological modifications of the dopaminergic tone. A central dopaminergic defect and an increased prolactin turnover with attendant reduction of the intracellular hormone pool may both be involved in the reduced prolactin release following provocative stimuli in patients with prolactinoma.
Insights
This study found no significant differences in prolactin secretion patterns between micro- and macroprolactinoma patients when their central dopaminergic tone was pharmacologically altered. These findings suggest similar underlying mechanisms for both types of prolactin-secreting tumors.
Area of Science:
- Endocrinology
- Neuroendocrinology
- Oncology
Background:
- Prolactin-secreting tumors (prolactinomas) are classified as micro- or macroprolactinomas based on size.
- Previous research suggested differing dopaminergic regulation of prolactin release between these subtypes.
- Understanding these differences is crucial for diagnosis and treatment.
Purpose of the Study:
- To investigate and compare the prolactin secretory patterns in response to pharmacological manipulation of central dopaminergic tone in patients with micro- and macroprolactinomas.
- To determine if dopaminergic regulation differs between micro- and macroprolactinomas.
Main Methods:
- A study involving 32 prolactinoma patients (19 micro, 13 macro) and 10 healthy controls.
- Three pharmacological tests were administered: saline infusion, metoclopramide administration, and dopamine infusion combined with metoclopramide.
- Plasma prolactin levels were measured to assess secretory patterns.
Main Results:
- Dopamine infusion significantly decreased prolactin in all groups, with no difference between micro- and macroprolactinoma patients.
- Metoclopramide significantly increased prolactin in prolactinoma patients, but less than in controls; no difference was seen between prolactinoma subtypes.
- Dopamine enhanced the metoclopramide-induced prolactin increase in both prolactinoma groups, but not in controls.
Conclusions:
- No significant differences were observed in prolactin secretory patterns between micro- and macroprolactinoma patients during pharmacological dopaminergic modulation.
- A central dopaminergic defect and increased prolactin turnover may explain reduced prolactin release in prolactinoma patients.
- These findings challenge previous assumptions of distinct dopaminergic regulation based on tumor size.
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