title: The third phase of in vitro insulin secretion. Evidence for glucose insensitivity.
abstract: In this study, in vitro B-cell models are described, which may be applicable for studying the reported B-cell desensitization produced by hyperglycemia in IDDM and NIDDM. Using a programmable perifusion/perfusion system, insulin secretion from perifused islets was measured at 10-30-min intervals for 24-50 h. After 3-4 h continuous glucose (11 mM), a new phase of insulin release occurs in which secretion declines to, and remains at, approximately 25% maximal release. Results were similar when using: perifused islets embedded in Cytodex 3, or Bio-Gel P-2, 100-200 mesh; batchincubated islets with hourly changes of medium; and the isolated pancreas perfused for 8 h. Three different media, Hana HB 104 (fortified, fully defined medium), RPMI-1640 + 10% FBS, and perfusion bufferalbumin, were used. Despite reduced secretion to continuous glucose, each system responded vigorously to an acute stimulation with glucose-forskolin. Decreased secretion was primarily caused by decreased secretagogue efficiency (reduced fractional secretion). Prolonged stimulation with glucose or glucose-IBMX produced a similar waning of secretion regardless of the amount of insulin released. It is concluded that the third phase of insulin secretion may represent a secret-agogue-induced, signal desensitization of the B-cell, rather than exhaustion of a B-cell compartment of stored insulin.
mesh_terms: D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D003470:Culture Media; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D013997:Time Factors
chemical_list: D003470:Culture Media; D007328:Insulin; D005576:Colforsin; D005947:Glucose