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Pituitary (2007) 10:233236 DOI 10.1007/s11102-007-0044-8
Mechanism of action of octreotide in acromegalic tumours in vivo using dynamic contrast-enhanced magnetic resonance imaging
Thozhukat Sathyapalan Martin Lowry Lindsay W Turnbull Chris Rowland-Hill Stephen L Atkin
Published online: 31 May 2007 Springer Science+Business Media, LLC 2007
Abstract Context Octreotide causes signicant tumour shrinkage in patients with acromegaly but the exact mechanism of action is unclear in vivo.Objective To determine the mechanism of action of octreotide in vivo using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Design Five patients with acromegaly were treated with octreotide as primary medical therapy. DCE-MRI was done at baseline and 24 weeks. Local ethical committee approval was granted.Setting Study was done in a tertiary care centre. Patients Five patients with newly diagnosed acromegaly were recruited.Intervention Patients were started on subcutaneous octreotide and DCE-MRI was done on 0 and 24 weeks. Main outcome measures Amplitude of contrast intake, exchange rate and maximum enhancement index of tumour tissue was compared before and after treatment. Results Amplitude of contrast intake (9.87 3.52 vs.4.97 1.96 P 0.05) and exchange rate (6.27 1.57 vs.1.63 0.76 P value 0.01) were signicantly higher at baseline in adenoma compared to normal pituitary tissue but was comparable to normal pituitary tissue after
treatment. There was a signicant decrease in amplitude of contrast intake and exchange rate which relates to functional vascularity of adenoma at 24 weeks compared to baseline (P-values 0.026 and 0.002 respectively) but there were no signicant changes in the normal pituitary tissue. Conclusion DCE-MRI in acromegalic tumours treated with octreotide showed a signicant reduction in functional vascularity after octreotide therapy compared to baseline in pituitary adenomas. This supports the antiangiogenic action of somatostatin analogue therapy in vitro, but it remains unclear if this mechanism is important clinically in analogue pre-treatment reducing the effect of radiotherapy on these pituitary tumours.
Keywords DCE-MRI Acromegaly Angiogenesis Octreotide Dopamine agonist
Somatostatin analogue therapy is associated with signi-cant tumour shrinkage in patients with acromegaly [1, 2]. How this may occur is unclear and there is evidence for a number of potential mechanisms. Native somatostatin has been shown to inhibit the proliferation of both normal and tumorous cells in vitro, data that would be in accord with the observations of somatostatin receptors 1, 2, 4, and 5...