Mechanism of action of octreotide in acromegalic tumours in vivo using dynamic contrast-enhanced magnetic resonance imaging.
BACKGROUND
Octreotide causes significant 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).


METHODS
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.


METHODS
Study was done in a tertiary care centre.


METHODS
Five patients with newly diagnosed acromegaly were recruited.


METHODS
Patients were started on subcutaneous octreotide and DCE-MRI was done on 0 and 24 weeks.


METHODS
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 < or = 0.05) and exchange rate (6.27 +/- 1.57 vs. 1.63 +/- 0.76 P value < or = 0.01) were significantly higher at baseline in adenoma compared to normal pituitary tissue but was comparable to normal pituitary tissue after treatment. There was a significant 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 significant changes in the normal pituitary tissue.


CONCLUSIONS
DCE-MRI in acromegalic tumours treated with octreotide showed a significant 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.
Sathyapalan
Thozhukat
T
Department of Medicine, University of Hull, Anlaby Road, Hull HU3 2JZ, UK. tsathyapal@rediffmail.com
Lowry
Martin
M
Turnbull
Lindsay W
LW
Rowland-Hill
Chris
C
Atkin
Stephen L
SL
D000172:Acromegaly / Q000188:drug therapy*; D000236:Adenoma / Q000098:blood supply / Q000188:drug therapy*; D000328:Adult; D000368:Aged; D020533:Angiogenesis Inhibitors / Q000627:therapeutic use*; D018931:Antineoplastic Agents, Hormonal / Q000493:pharmacokinetics / Q000627:therapeutic use*; D003287:Contrast Media; D019008:Drug Resistance, Neoplasm; D005260:Female; D019786:Gadolinium DTPA; D049912:Growth Hormone-Secreting Pituitary Adenoma / Q000098:blood supply / Q000188:drug therapy*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015282:Octreotide / Q000493:pharmacokinetics / Q000627:therapeutic use*; D012039:Regional Blood Flow / Q000187:drug effects; D013004:Somatostatin / Q000031:analogs & derivatives / Q000627:therapeutic use
D020533:Angiogenesis Inhibitors; D018931:Antineoplastic Agents, Hormonal; D003287:Contrast Media; D013004:Somatostatin; D019786:Gadolinium DTPA; D015282:Octreotide