This study investigated quantitated expression of
dopamine 2 receptor (D2R) and
somatostatin receptors of the five types (SSTR1-SSTR5) in a large series of clinically non-functioning
pituitary adenomas (CNFAs). Co-expression of these receptors in individual
adenomas was studied as well as correlation between receptor types.
Adenoma tissue from 198 patients who underwent surgery for CNFAs was analyzed by immunohistochemistry and quantitative real-time PCR. D2R and SSTR1-3
mRNA was expressed in all 198
adenomas. SSTR4 and SSTR5 were detectable in 85 % and 61 % of
adenomas, respectively. Expression of D2R was significantly higher than that of the
somatostatin receptors. The median relative expressions were as follows from highest D2R >> SSTR3 > SSTR2 >
SSTR1 > SSTR5 > SSTR4. High relative expression (ratio to
beta-glucuronidase mRNA > 1) of D2R was found in 60 % of
tumors, high expression of
SSTR1 in 7.5 %, SSTR2 in 7 %, SSTR3 in 4 % and SSTR5 in 0.5 %. The quantity of D2R correlated positively with expression of SSTR2 and SSTR3, and negatively with
SSTR1 and SSTR5. Among histological
adenoma types,
SSTR1 was significantly higher in null-cell
adenomas and SSTR3 was lower in silent
corticotroph adenomas. In conclusions, in CNFAs, high expression of
somatostatin receptors is much less common than that of D2R, and co-expression of both these receptors is exceptional. D2R and SSTR3 seem to be the most promising targets for pharmacological treatment.