The Novel Somatostatin Ligand (SOM230) Regulates Human and Rat Anterior Pituitary Hormone Secretion

Currently available somatostatin analogs predominantly bind to the somatostatin receptor subtype (SSTR)2 subtype, and control GH and IGF-I secretion in approximately 65% of patients with acromegaly, their efficacy relating to receptor density and subtype expression. SOM230 is a somatostatin ligand with high affinity to four SSTR subtypes. In primary cultures of rat pituicytes, SOM230 dose-dependently inhibited GH release (P = 0.002) with an IC50 of 1.2 nm. Ten nanomoles SOM230 inhibited GH and TSH release by 40 ± 7% (P < 0.001) and 47 ± 21% (P = 0.09), respectively. No effect of SOM230 was observed on prolactin (PRL) or LH release. In cultures of human fetal pituitary cells, SOM230 inhibited GH secretion by 42 ± 9% (P = 0.002) but had no effect on TSH release. SOM230 inhibited GH release from GH-secreting adenoma cultures by 34 ± 8% (P = 0.002), PRL by 35 ± 4% from PRL-secreting adenomas (P = 0.01), and α-subunit secretion from nonfunctioning pituitary adenomas by 46 ± 18% (P = 0.34). In contrast, octreot...