Somatostatin analogs and
dopamine agonists are clinically used for medical
therapy of functioning
pituitary tumors, such as
growth hormone- and
prolactin-secreting
tumors, however, their effects on
ACTH-secreting
tumors are controversial. This study was aimed to determine whether
somatostatin receptor (SSTR) subtype (1-5) and
dopamine receptor type 2 (D2R) are differentially expressed in
pituitary tumors causing
Cushing's disease (CD), silent
corticotroph adenoma (SCA), and non-functioning
pituitary tumor (NFT). Tissue specimens were obtained from 35
pituitary tumors during transsphenoidal surgery. The steady-state
mRNA levels of SSTR1-5 and D2R genes were determined by real-time reverse-transcription polymerase chain reaction. Both
SSTR1 and 2
mRNA levels in SCA were greater than CD, while
SSTR1 mRNA levels, but not SSTR2, in SCA were also greater than NFT. SSTR5
mRNA levels in CD were greater than SCA, but did not differ between NFT and SCA. SSTR4
mRNA expression was undetectable. D2R
mRNA levels were markedly lower in CD and SCA than in NFT. The present study suggests that
somatostatin analogs more selective for SSTR5 and for
SSTR1 and/or 2may have the therapeutic potential for medical treatment of CD and SCA, respectively, whereas clinical application of
dopamine agonists selective for D2R is very limited in either CD or SCA.