Recent evidence suggests that somatostatin-28 (SRIF-28), cleaved from prosomatostatin by cells of the upper intestine, acts as a nutrient-stimulated inhibitor of insulin secretion in healthy men. A role for SRIF-28 in the pathophysiology of diabetes has not been previously explored, although several groups have measured circulating somatostatinlike immunoreactivity (SLI) in diabetic subjects. To investigate the possible mediation of abnormal insulin secretion in diabetes by SRIF-28, plasma levels were measured in 10 non-insulin-dependent diabetic men and 9 age- and weight-matched control subjects. Concentrations of SRIF-14 and SLI were also obtained. Subjects were admitted for study after an overnight fast, blood was collected before and at 30-min intervals for 4 h after a fat meal, and plasma samples were analyzed for SRIF-28 and SRIF-14 by specific methods. Basal glucose levels in the diabetic men were significantly higher than in control subjects (10.2 ± 1 vs. 5.8 ± 0.2 mM), but insulin levels were similar (79 ± 14.2 vs. 93.3 ± 14.2 pM). The diabetic men had significantly lower basal SRIF-28 levels than the control subjects (11.4 ± 0.6 vs. 14.6 ± 1.0 pM, P = 0.017). After fat intake, SRIF-28 levels throughout the 4 h of study were indistinguishable in the two groups (270 vs. 292% of basal). Basal SRIF-14 and SLI levels were not significantly different in the two groups, and SRIF-14 and SLI concentrations rose similarly after the meal. There were no correlations between basal SRIF-28 and glucose or insulin levels. The lower concentrations of the β-cell inhibitor SRIF-28 in diabetic men may represent an adaptation to relative insulin deficiency.

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