Radioimmunoassay of Human Plasma Somatostatin

Mackes, K. G.; Itoh, Mitsuyasu; Greene, Kate; Gerich, John E.

doi:10.2337/diab.30.9.728

Cited by 27 publications

(11 citation statements)

References 11 publications

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“…13 ' 14 The nature of the high-molecular-weight SLI fraction is uncertain, although we have confirmed previous observations that its molecular size is greater than 150,000 daltons 15 and that it does not dissociate in 10% acetic acid nor increase when SRIF, [des-Ala']-SRIF, or S-28 are added to plasma (unpublished data).…”

Section: Resultssupporting

confidence: 71%

Evidence for the presence of somatostatin 28 in plasma

Shoelson¹,

Polonsky²,

Docherty³

et al. 1982

Diabetes

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SUMMARYSomatostatin-like immunoreactivity (SLI) from dog and rat plasma eluted from Biogel P-6 columns as three distinct peaks. A large-molecular-weight peak was present in the void volume of the column, an intermediate-sized peak (SLI 28) coeluted with synthetic somatostatin 28 (S-28), and a small-molecular-weight peak (SLI 14 ) coeluted with SRIF. Material from the SLI 28 peak diluted in parallel to the S-28 standard in the radioimmunoassay and behaved identically to S-28 on high pressure liquid chromatography (HPLC). Levels of SLI 28 in the portal vein were consistently greater than the simultaneously measured peripheral levels (portal peripheral ratio 2.2 ± 0.2). Venous samples drawn from multiple sites suggested that SLI 28 is secreted by the duodenum and/or pancreas and the intestine. This data is consistent with the possibility that S-28 is a hormone distinct from SRIF. DIABETES 37: 474-477, May 1982.

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Section: Resultssupporting

confidence: 71%

Evidence for the presence of somatostatin 28 in plasma

Shoelson¹,

Polonsky²,

Docherty³

et al. 1982

Diabetes

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“…Recovery of total plasma SLI added to the columns was 96.2±9.1% (n = 10).The values in panel B represent the SLI content of each peak obtained after extraction of 10 ml of plasma on C-18 cartridges with subsequent gel filtration of the extract on Bio-gel P-6 columns. The value for the SLI content in each peak in panel B was divided by 10 to facilitate comparison with the values in panel A. each of which is present in very low concentration (7-9); (b) circulating somatostatin binding factors that interfere with the somatostatin assay, have been reported (8, 9) and (c) proteolytic enzymes in plasma have been shown to degrade the SRIF tracer under certain conditions (7,9,10). These methodological difficulties have resulted in significant controversy concerning the level and nature of circulating SLI.…”

Section: Discussionmentioning

confidence: 99%

Plasma somatostatin 28 increases in response to feeding in man.

Polonsky¹,

Shoelson²,

Docherty³

1983

J. Clin. Invest.

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A B S T R A C T Tissue somatostatin-like immunoreactivity (SLI) consists of a number of molecular species including the cyclic tetradecapeptide or SRIF, an Nterminally extended form of SRIF termed somatostatin-28, as well as larger precursor peptides. The function and nature of circulating SLI is not well understood. In this report, we describe techniques for the definition of the components of plasma SLI in normal human plasma. Plasma SLI measured after gel filtration on Bio-gel P-6 columns was found to consist of from 1-3 peaks. The void volume peak was present in greatest concentration (34.2±8.9 pg/ml) and did not increase in response to a mixed meal. Very low levels of two additional peaks of SLI activity were found. To further characterize these peaks, 10-ml plasma samples were extracted and concentrated on octadecylsilyl silica (C-18) cartridges with subsequent fractionation on Bio-gel P-6 columns. The two peaks that coeluted with synthetic SRIF and S-28 markers, respectively, were present in concentrations of 5.4±1.4 and 4.8±1.9 pg/ml in fasting plasma. In response to a mixed meal, the SLI14 peak doubled (12.9±2.4 pg/ml) while the SLI28 peak increased to 29.9±7.2 pg/ml at 120 min. These results provide evidence that S-28 circulates in human plasma and its increase after feeding is consistent with a possible biological role for this peptide.

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“…These data showed heterogeneity of plasma SLI but the large forms did not differ from synthetic S-14 in binding with anti-S-14 antibody since dilution curves paralleled the standard S-14 curve. The nature of'big' somatostatin was uncer¬ tain because it could be a binding of S-14 with a large molecular weight plasma component (Colon, Srikant, Ipp et al 1978;Mackes, Itoh, Greene & Gerich, 1981) or a non-specific interference of plasma proteins in the antibody-antigen reaction (Colon, Bridgeman & Alberti, 1982); in the duck, however, it was unlikely to be an aggregate form of S-14 or protein-bound S-14 since it was always present after chromatography studies, with 8 M-urea and 0-2 M-acetic acid (Fig. 4), conditions which tended to dissociate non-covalently bound S-14.…”

Section: Discussionmentioning

confidence: 99%

Characterization of somatostatin in peripheral and portal plasma in the duck: in-vivo metabolism of somatostatin-28 and-14

Guenot¹,

Strosser²,

Mialhe³

1984

Journal of Endocrinology

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A sensitive and specific radioimmunoassay without an extraction step was developed for somatostatin in duck plasma. Degradation of Tyr1-125I-labelled somatostatin-14 (S-14) averaged 2% for blood collected with EDTA and zymofren. Recovery of somatostatin-like immunoreactivity (SLI), added to the plasma, averaged 91% for S-14 and 86% for S-28. Chromatographic analysis of portal plasma on Sephadex G-25 showed three peaks: one peak coeluted with cytochrome c (mol. wt 12500) in the void volume and was called 'big' somatostatin; of the two smaller forms, one coeluted with synthetic S-28 and the other with synthetic S-14; these were immunologically and physicochemically indistinguishable from synthetic S-28 and S-14. In peripheral plasma only the large form of somatostatin, 'big' somatostatin, was found. The mean portal plasma concentration of SLI was 4.1 +/- 0.41 microgram/l (n = 11, range 2.8-5.1 micrograms/l). In peripheral plasma the SLI concentration was 1.05 +/- 0.45 microgram/l (n = 11, range 0.84-1.2 microgram/l). The metabolic clearance rate, distribution volume and calculated half-life values were 63.1 +/- 14 ml/kg per min, 40.9 +/- 8.9 ml/kg and 1.06 +/- 0.19 min for S-14 compared with 45.7 +/- 7 ml/kg per min, 14.8 +/- 2.5 ml/kg and 2.14 +/- 0.54 min for S-28. These results indicated that S-28 was cleared from plasma at a slower rate than S-14 in the duck. It was concluded that: (1) portal plasma SLI was four times higher than peripheral SLI; (2) SLI in portal plasma existed as 'big' somatostatin, S-28 and S-14, whereas in peripheral plasma it existed mainly as 'big' somatostatin; (3) in-vivo studies indicated that S-28 was metabolized less rapidly than S-14.

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Radioimmunoassay of Human Plasma Somatostatin

Cited by 27 publications

References 11 publications

Evidence for the presence of somatostatin 28 in plasma

Evidence for the presence of somatostatin 28 in plasma

Plasma somatostatin 28 increases in response to feeding in man.

Characterization of somatostatin in peripheral and portal plasma in the duck: in-vivo metabolism of somatostatin-28 and-14

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