Expression and Function of Somatostatin Receptor Subtype 1 in Human Growth Hormone Secreting Pituitary Tumors Deriving from Patients Partially Responsive or Resistant to Long-Term Treatment with Somatostatin Analogs

The role of somatostatin (SS) receptor subtype 1 (SSTR 1 ) in mediating the inhibitory effect of SS on growth hormone (GH) secreting pituitary tumors has been recently demonstrated. In the present study, we evaluated the effect of the selective SSTR 1 agonist BIM-23745 on in vitro GH secretion in GH-secreting pituitary tumor cells, deriving from patients resistant or partially responsive to octreotide long-acting release (octreotide-LAR) or lanreotide therapy in vivo and expressing SSTR 1 mRNA. In addition, the inhibiting effect of BIM-23745 on the GH secretion was compared with that of octreotide. Our data demonstrate that (1) SSTR 1 receptor was present in 56.25% (9/16) of the GH-secreting adenomas examined; (2) in all GH-secreting pituitary tumors that expressed SSTR 1 , BIM-23745 significantly inhibited GH secretion in vitro, and (3) when SSTR 1 subtype was present in tumors from patients resistant to octreotide-LAR or lanreotide therapy, BIM-23745 was able to inhibit the in vitro GH secretion. In conclusion, the results of the current study suggest that SS analogs selective for the SSTR 1 may represent a further useful approach for the treatment of acromegaly in patients resistant or partially responsive to octreotide-LAR or lanreotide treatment in vivo.