Circulating somatostatin concentrations in healthy and non-insulin-dependent (type II) diabetic subjects

A technically simple radioimmunoassay for somatostatin-like immunoreactivity (SLI) in human plasma, which uses polyethylene glycol 6000 to precipitate tracer-degrading enzymes and high molecular weight interfering components, is described and validated. Fasting concentrations of SLI in peripheral plasma were similar in healthy and non-insulin-dependent diabetic (NIDD) subjects (range 3-39 pg/ml) but showed fluctuations for individuals in both groups when sampled frequently over a 60-min period. The mean coefficient of variation of SLI concentration was, however, less (8.0%; range 3-13%) in the diabetic group than in age-matched healthy subjects (19.5%; range 11-44%) (P less than 0.02). Thus the regulation of basal D cell activity or of the somatostatinergic nervous system may be altered in type II diabetic subjects. A hospital breakfast (550 kcal) was a weak stimulus for release of SLI in both healthy and diabetic subjects. The rise in plasma SLI was sustained over 120 min. An increment in plasma SLI over mean basal levels of 5.9 +/- 0.8 pg/ml was observed in young (mean age 23 yr; N = 6) control subjects, 7.9 +/- 2.0 pg/ml in older (mean age 55 yr; N = 7) control subjects and 5.9 +/- 0.6 pg/ml (mean age 62 yr; N = 7) in diabetics. Oral glucose (75 g) produced only a transient and erratic rise in plasma SLI that was not significant at any time point for either healthy or NIDD subjects. It is concluded that further investigations are necessary before hypotheses linking somatostatin deficiency with the hormonal and metabolic abnormalities of non-insulin-dependent diabetes can be accepted.