Adrenocortical adenomas display highly variable expressions of
somatostatin receptor (SSTR) subtypes, whose expression is mandatory (although not always sufficient) to achieve the positive effects of
somatostatin (SST) analog
therapy. Immunohistochemistry (IHC) is the main method used to investigate receptor
protein expression. The molecular biology method - polymerase chain reaction (PCR) - is also often used to investigate receptor expression. Nevertheless, the expression of receptor
mRNA and the respective receptor
protein is not always synchronized. The aim of this study was to investigate SSTR expression by IHC in adrenal
adenomas, to compare the results to data obtained by real-time PCR and to determine whether hormonally functioning and non-functioning
adenomas differ in this respect.
Adrenocortical adenomas were removed surgically from 13 females and 2 males. The tissues were obtained from 9 non-functioning and 6 functioning
adenomas. The intensity of IHC reaction was scored semiquantitatively by two independent observers. Real-time PCR was performed using pairs of primers in a reaction amplified along a gradient of temperatures. Amplified
DNA was measured by monitoring
SYBR-Green fluorescence. In non-functioning
tumors, compatibility between IHC and PCR results was observed for
SSTR 1 and 2 in 62.5% of the samples. Fifty percent of patients demonstrated compatibility for SSTR 4 and 5 and 37.5% for SSTR 3. In hormonally active
adenomas, total compatibility of both methods was noted for
SSTR 2 (100%). The compatibility obtained for SSTR 5 was 66.6%. We conclude that receptor gene and respective receptor
protein expression are not always synchronized.
Messenger RNA detection alone is not sufficient to predict the presence of the receptor
protein acting as a target for SST and its analogs.