Dopamine D2 receptor imaging in pituitary adenomas using iodine-123-epidepride and SPECT.
Epidepride is a novel benzamide derivative with high affinity for D2 receptors. Epidepride, in its 123I-labeled form, can be used for SPECT imaging of striatal and extrastriatal dopamine D2 receptors. The present study evaluated the usefulness of epidepride and SPECT for in vivo imaging of dopamine receptors in pituitary adenomas.


METHODS
SPECT imaging was performed in 19 patients with pituitary adenomas (among them 9 patients had prolactinoma, 4 acromegaly, 4 clinically nonfunctioning pituitary adenoma, 1 Cushing's disease and 1 Nelson's syndrome) and 7 control subjects 180 min after intravenous bolus injection of 3.9 +/- 1.1 mCi [123I]epidepride. The ratio target/cerebellum minus 1, reflecting specific/ nonspecific binding was used as semiquantitative measure of D2 receptor binding.


RESULTS
Eight of nine prolactinoma patients demonstrated specific binding within the adenoma. The adenoma/ cerebellum ratio 3 hr p.i. showed a wide variation with values from 2.5-33. In three prolactinomas, binding was higher than in the striatum. Specific binding within the lower range of prolactinomas (adenoma/cerebellum ratios 2 and 4.8) could be demonstrated in two of four GH-secreting adenomas. All four nonfunctioning tumors showed specific binding. The adenoma/cerebellum ratio was within the lower range of prolactinomas (5.2-7.5) in three of these patients but extremely high in one (52.3). No specific tracer uptake could be demonstrated in patients with Cushing's disease or Nelson's syndrome. The striatum/cerebellum ratio 3 hr p.i. in pituitary adenoma patients was not significantly different from control subjects (17.3 +/- 5.5 versus 17.8 +/- 6.6; patients versus control subjects).


CONCLUSIONS
Epidepride appears to be an excellent ligand for in vivo imaging of dopamine D2 receptors in pituitary adenomas. Epidepride SPECT could serve as a predictor for response to dopamine agonist treatment.
Pirker
W
W
University Clinic for Neurology and Nuclear Medicine, Vienna, Austria.
Riedl
M
M
Luger
A
A
Czech
T
T
Rössler
K
K
Asenbaum
S
S
Angelberger
P
P
Kornhuber
J
J
Deecke
L
L
Podreka
I
I
Brücke
T
T
D000172:Acromegaly / Q000209:etiology; D000236:Adenoma / Q000737:chemistry / Q000150:complications / Q000000981:diagnostic imaging* / Q000188:drug therapy; D000293:Adolescent; D000328:Adult; D000368:Aged; D001549:Benzamides; D001971:Bromocriptine / Q000627:therapeutic use; D002531:Cerebellum / Q000737:chemistry / Q000000981:diagnostic imaging; D003342:Corpus Striatum / Q000737:chemistry / Q000000981:diagnostic imaging; D003480:Cushing Syndrome / Q000209:etiology; D018491:Dopamine Agonists / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008090:Lisuride / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009347:Nelson Syndrome / Q000209:etiology; D010911:Pituitary Neoplasms / Q000737:chemistry / Q000150:complications / Q000000981:diagnostic imaging* / Q000188:drug therapy; D015175:Prolactinoma / Q000000981:diagnostic imaging; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2 / Q000032:analysis*; D015899:Tomography, Emission-Computed, Single-Photon
D001549:Benzamides; D018491:Dopamine Agonists; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; C063525:epidepride; D001971:Bromocriptine; D008090:Lisuride