Expression of somatostatin receptors on human pituitary adenomas in vivo and ex vivo

The distribution and biologic activity of somatostatin receptor subtypes (S STR) in pituitary adenomas is not clarified, especially regarding clinicall y non-functioning adenomas (NFPA). We therefore characterized SSTR in human pituitary adenomas by combining molecular biology and in vivo scintigraphy . Go-expression of gonadotropin-releasing hormone receptor (GnRH-R) mRNA wa s also assessed to see whether this feature was associated with adenoma sub type and SSTR status. Pituitary tumor biopsies were obtained during transsp henoidal adenomectomy from 21 patients (11 NFPA, 7 acromegalics, 2 prolacti nomas, 1 Gushing's disease). Expression of mRNA encoding the 5 known SSTR s ubtypes and the GnRH-R was determined by RT-PCR. Twelve patients also under went a pre-operative somatostatin receptor scintigraphy. Most adenomas (no. = 18) expressed mRNA for more than one SSTR. SSTR2 mRNA was expressed in 1 8 cases, whereas SSTR4 was absent in all but one. SSTR3 was frequently expr essed in NFPAs. Somatostatin receptor scintigraphy was positive in most cas es, and with a significantly higher uptake index in GH-producing adenomas a ll of which expressed SSTR2 mRNA. The uptake index appeared to be related t o receptor density rather than tumor volume. Expression of GnRH-R mRNA was found in both NFPAs and GH-producing adenomas and was not significantly ass ociated with a particular SSTR subtype population. In conclusion: 1) the di stribution of SSTR is not significantly different between NFPA and GH-produ cing adenomas; and 2) somatostatin receptor scintigraphy reveals a higher u ptake in GH-producing adenomas which is not significantly related to either SSTR distribution or tumor volume. (J. Endocrinol. Invest. 24: 430-437, 20 01) (C) 2001, Editrice Kurtis.