Summary
The plasma levels of Somatostatin (SRIF) were studied in normal subjects and patients
with various disorders by a sensitive and specific radioimmunoassay. In 45 normal
subjects, the fasting plasma SRIF concentrations were 13.3 ± 5.3 pg/ml (mean ± SD).
Very high concentrations of plasma SRIF, ranging from 125.0 pg/ml to 400.0 pg/ml,
were found in all four patients with medullary carcinoma of the thyroid examined and
the SRIF levels were changed in parallel with their clinical course after resection
of the tumor. A case of pheochromocytoma also showed a relatively high SRIF concentration
in plasma (47.0 pg/ml), but the plasma SRIF level decreased to 8.7 pg/ml after removal
of the tumor. In normal subjects, plasma SRIF levels did not fluctuate during 2 hr-observation
period in basal state. Glucagon (1 mg, iv) and secretin (3 CHRU/kg B.W., iv infusion
over 30 min) had no effect on the SRIF levels in the peripheral blood plasma of normal
subjects. On intravenous infusion of arginine (0.5 g/kg B.W.) over 30 min, all 6 normal
subjects showed a significant increase in plasma SRIF 30-45 min after the start of
the infusion (basal value, 11.6 ± 1.5 pg/ml; peak value, 27.2 ± 3.0 pg/ml; p < 0.005).
Two cases of medullary thyroid carcinoma showed exaggerated responses after the arginine
administration (increases of 103 pg/ml and 157 pg/ml, respectively), suggesting that
SRIF was released from the tumor. These findings indicate that plasma SRIF determination
in the basal state and after arginine administration is useful for detecting and following
up SRIF-producing tumors.
Key-Words:
Plasma Somatostatin
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Arginine Infusion Test
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Tumor Marker
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Medullary Thyroid Carcinoma
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Pheochromocytoma
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Somatostatin-Producing Tumor
