Expression of SSTR2a,but not of SSTRs 1,3,or 5 in somatotroph adenomas assessed by monoclonal antibodies was reduced by octreotide and correlated with the acute and longterm effects of octreotide

CONTEXT:Reduced expression of somatostatin receptors(SSTRs)in somatotroph adenomas and their potential down-regulation after medical treatment may explain the unsatisfactory response to octreotide in particular acromegalic patients.The expression of SSTRs other than SSTR2a has not been studied in large,unselected cohorts using novel rabbit monoclonal antibodies.OBJECTIVE:We aimed to determine the expression of SSTRs 1,2a,3,and 5 in somatotroph adenomas,to correlate expression with clinical characteristics and the response to octreotide,and to ascertain whether preoperative octreotide treatment affected SSTR expression.DESIGN,SETTING,PATIENTS:The study included 75 adenomas from patients operated on consecutively during 2000 to 2010.After exclusion of 13 patients,immunohistochemical analysis with rabbit monoclonal antibodies against SSTRs 1,2a,3,and