Effect of dopamine agonists on prolactinomas and normal pituitary assessed by dynamic contrast enhanced magnetic resonance imaging (DCE-MRI).

Context: Dopamine agonists (DA) may act on prolactinoma size and secretion through additional effects on adenoma vascularity that can be visualized using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI).

Objective: We hypothesized that DAs may exert their effect through a change in tumour functional vascularity leading to a reduction of prolactin (PRL) levels and tumour size.

Subjects And Methods: To investigate this, 23 subjects were studied comprising five with macroprolactinomas, 11 with microprolactinomas, seven with non-lesion hyperprolactinemia and 15 normal volunteers (including five females on oral contraceptive pills). Patients with macroprolactinomas were treated with cabergoline 4 mg weekly and microprolactinomas were treated with quinagolide 75 microg daily for the duration of study. DCE-MRI was performed immediately pre-treatment and at 3-4 days, 1 and 3-4 months after treatment. Normal volunteers took three 75 microg quinagolide doses and were scanned pre-treatment and at 3 days. Data were analysed using the Brix model, producing a measure of vascular permeability and leakage space.

Results: PRL levels were significantly reduced in all patients and volunteers. Vascular parameters decreased significantly for four of five macroprolactinomas and all microprolactinomas which were maintained during the treatment period (p < 0.01). No changes were seen in normal volunteers or non-lesion hyperprolactinemia. One of five macroprolactinomas showed no change in either permeability or tumour size.

Conclusion: Functional prolactinoma vascularity differs from non-lesion hyperprolactinemic pituitary and normal pituitary, and is responsive to DA therapy. The reduction in vascular parameters precedes shrinkage in macroprolactinomas, and if not seen within days of treatment may indicate DA resistance requiring early surgery.