Somatostatin often serves to inhibit secretory responses, but also exhibits antiproliferative effects in some tissues [14]. Somatostatin receptors are widespread throughout the central nervous system and in several peripheral tissues [15, 16]. To date, 5 somatostatin receptor subtypes (sstr) have been identified and cloned (sstr1–sstr5) [14]. Immunostaining indicates that normal human anterior pituitary expresses all 5 subtypes, and that most corticotroph adenomas express ≥1 sstr [17–19]. While expression levels are highly variable, sstr2 and sstr5 are most consistently expressed, and sstr4 is generally absent [17, 19]. A study using quantitative RT-PCR and immunohistochemistry found that human corticotroph adenomas expressed sstr1,2,4 and 5, and that sstr5 had the highest expression levels in 10/12 adenomas [20].