Sensitive radioimmunoassay for immunoreactive somatostatin in extracted plasma: measurement and characterization of portal and peripheral plasma in the rat
The RIA of immunoreactive somatostatin (IRS) in unextracted rat plasma has proved difficult because of marked tracer degradation. The presence of 0.1 ml plasma in standard curve tubes resulted in more than 80% damage to (Tyr/sup 1/-/sup 125/I)-somatostatin (SRIF) and only 2.7% binding compared to 38% in plasma free buffer. Sephadex gel filtration of (Tyr/sup 1/-/sup 125/I)SRIF after plasma incubation showed that most of the radioactivity was converted to a lower molecular weight fragment with no immunoreactivity. Destruction of (Tyr/sup 1/-/sup 125/I)SRIF was overcome by extraction of plasma with acid-ethanol in a simple 1-step procedure. With this technique, recovery of synthetic SRIF from plasma averaged 93.8%. Assay sensitivity was 30 pg IRS/ml plasma. Exogenous SRIF incubated with rat blood was rapidly inactivated. The mean portal plasma IRS level was 310 pg/ml in good agreement with the IRS content of pooled portal plasma of 346 pg/ml found by affinity chromatography. In 18 inferior vena cava (IVC) samples, the IRS level ranged between less than 30 and 44 pg/ml in 16 samples and 90 and 155 pg/ml in the remainder. On Sephadex G-25 columns, IRS in portal plasma extracts eluted as two approximately equal peaks. It is concluded that in the rat: (1) SRIF and tracer SRIF are rapidly inactivated by blood; (2) portal plasma IRS is 7 times higher than IVC IRS; and (3) IRS in portal plasma exists as SRIF and big SLI, in IVC it exists mainly as big SLI.
- Research Organization:
- McGill Univ., Montreal, Canada
- OSTI ID:
- 5007937
- Journal Information:
- Endocrinology; (United States), Vol. 107:1
- Country of Publication:
- United States
- Language:
- English
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