Fifty-one adrenal
pheochromocytomas and 14
paragangliomas were evaluated for
somatostatin (SRIH) receptor content with in vitro autoradiography on tissue sections from surgically removed
tumors, using iodinated
125I[Tyr]3 octreotide as radioligand. Thirty-seven of 51
pheochromocytomas were SRIH receptor positive (73%), as well as 13 of 14
paragangliomas (93%). These
SRIH receptors were of high affinity, pharmacologically specific for SRIH and localized on the
tumor tissue. Using in vivo imaging techniques with radiolabeled SRIH analogs,
paragangliomas could be visualized in five patients, as well as
pheochromocytomas in two of three patients. All
tumors tested subsequently in vitro (n = 7) were shown to contain
SRIH receptors. A majority of
pheochromocytomas were also shown to have a high tumoral SRIH content as measured by immunohistochemical techniques. Detection of SRIH
messenger RNA in
pheochromocytomas by in situ hybridization indicated that the SRIH was produced in the
tumors. A weak inverse correlation was observed between SRIH receptor status and tumoral SRIH content, suggesting that
SRIH receptors may be down-regulated by high levels of endogenous SRIH in some
tumors. There was no correlation between the SRIH receptor status and sex, age,
tumor size, benign vs. malignant
tumor, or urinary
metanephrine excretion. These
tumors were also analyzed for allelic losses on various chromosomes and showed significant loss of heterozygosity (LOH) on chromosomes 1p, 3p, 17p, and 22q. All eight
tumors with LOH on chromosome 1p were SRIH receptor positive (100%), whereas only 6 of 11
tumors without LOH on 1p (55%) were SRIH receptor positive, suggesting a correlation between LOH on 1p and SRIH receptor positive status.
SRIH receptors thus represent a consistent pathobiochemical marker for most of these adrenal and extra-adrenal
tumors. In addition, these receptors may be of potential interest for the in vivo localization of these
tumors.