We investigated the impact of
blood glucose normalization on plasma levels of
somatostatin-like immunoreactivity (SLI) in subjects with
C-peptide-negative
insulin-dependent diabetes mellitus (
IDDM) and in totally pancreatectomized patients. Patients were studied during
hyperglycemia and during normoglycemia, which was attained by Biostator-directed feedback
insulin infusion. The experiments were performed in the fasted state and after a standardized breakfast. In
IDDM (n = 6), basal levels of SLI were significantly higher than in nondiabetic subjects (n = 18). In
IDDM, normalization of
hyperglycemia was followed by a 40% decline in basal SLI (P less than .05). After the meal, SLI increased to the same absolute levels with or without feedback
insulin treatment; however, the incremental response was 60% higher during feedback
insulin treatment (P less than .05). Treatment also suppressed fasting and postprandial levels of
glucagon, whereas
gastric inhibitory polypeptide (GIP) levels were unaltered. In four pancreatectomized patients, normoglycemia tended to lower plasma levels of SLI by 50% (P less than .1). After breakfast, an SLI response was noted during normoglycemia, whereas no significant effect of the meal was seen during
hyperglycemia. We conclude that in
IDDM and in totally pancreatectomized patients, administration of
insulin with subsequent normalization of
blood glucose is accompanied by a decline in plasma levels of SLI in the fasted state, whereas the apparent response to a meal is enhanced. These effects on plasma levels of SLI probably reflect to a major extent release of
somatostatin from the gastrointestinal tract.