Endocrine Abstracts

Background: Dopamine agonists may act on prolactinoma size and secretion through additional effects on adenoma vascularity which can be visualised using Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI). To investigate this 23 subjects, 5 with macroprolactinomas (prolactin (PRL) range 14631-500000mU/L), 11 with microprolactinomas (PRL range 621-4777mU/L), 7 individuals with non-lesion hyperprolactinemia and 15 normal volunteers, including 5 females on oral contraceptive pills were studied. Patients were treated with cabergoline 4 mg weekly for macroprolactinomas and quinagolide 75μg daily for microprolactinomas. DCE-MRIs were performed before treatment, at 3–4 days, 1 month and 3–4 months after treatment. Normal volunteers took three 75μg quinagolide doses and were rescanned after 3 days. Obtained data was analysed using Tofts and Kermode two compartment model, estimating vascular permeability and leakage space.

Results: A significant reduction in PRL levels was seen for all patients and volunteers. A significant decrease in vascular parameters was observed in both macroprolactinomas and microprolactinomas which was maintained during the treatment period (p<0.01). No difference in pituitary vessel permeability was demonstrated for normal volunteers or subjects with non-lesion hyperprolactinemia either before or after 3 days treatment. 4 of 5 macroprolactinomas demonstrated a decrease in permeability of 75% at 1 month (p<0.0001) with a reduction in tumour size, which continued to decrease at 4 months. The single macroprolactinoma not showing a change in permeability was unchanged in size after 4 months treatment.

Conclusion: The functional vascularity of prolactinoma differs from non-lesion hyperprolactinaemic and normal pituitary, and is responsive to dopamine agonist therapy. The reduction in vascular parameters is a crucial step in macroadenoma shrinkage and precedes shrinkage. Macroprolactinomas not showing an early DCE-MRI treatment response may represent dopamine agonist resistance, requiring early surgery.