We have investigated the effects of chronically elevated glucose concentrations on the pancreatic -cell line TC1-6. We show that basal glucagon secretion and proglucagon gene expression were increased in response to high glucose levels. The extent of acute stimulated secretion of glucagon was also increased in response to high glucose, as was the transcription of the prohormone processing enzymes PC1/3 and PC2. The secretion of GLP-1, a proglucagon-derived peptide produced by cleavage of proglucagon by PC1/3, was also increased in response to high glucose. Gene expression profiling experiments showed that a number of components of the regulated secretory pathway were up-regulated at high glucose concentrations, including processing enzymes and exocytotic proteins. Immunoblot analysis showed that the expression of the exocytotic SNARE proteins, as well as that of PC1/3, chromogranin A, and 7B2, were all increased after chronic exposure to high glucose levels. Immunocytochemistry showed no changes in the expression of the mature -cell markers glucagon and brn-4 and no induction of the immature -cell marker pdx-1. We conclude that chronically elevated glucose concentrations up-regulate the regulated secretory response of the -cell. (Endocrinology 146: 4514?4523, 2005)

Excess excitatory amino acid release is involved in pathways associated with seizures and neurodegeneration. Thyrotropin-releasing hormone (TRH; protirelin), a brain-derived tripeptide, has shown efficacy in the treatment of such disorders, yet its mechanism of neuroprotection is poorly understood. Using superfused hippocampal slices, we tested the hypothesis that TRH could inhibit evoked glutamate/aspartate release in vitro. Rat hippocampal slices were first equilibrated in oxygenated Krebs buffer (KRB) (120 min) then superfused for 10 min with KRB (control), or KRB containing 0.1, 1, or 10 AM TRH respectively, prior to and during 5 min depolarization with high potassium KRB (50 mM [K+] T TRH). Fractions (1 min) were collected during the 5 min stimulation and for an additional 10 min thereafter and analyzed for glutamate and aspartate by HPLC. TRH had no effect on baseline glutamate/aspartate release, while all three TRH doses significantly ( P < 0.05) inhibited peak 50 mM [K+]-stimulated glutamate/aspartate release, and glutamate remained below control ( P < 0.05) at 15 min post stimulation. A 5 min pulse of TRH (10 AM) had no affect on basal glutamate/aspartate release, whereas the TRH prepulsed slices failed to release glutamate/aspartate by [K+]-stimulation given 15 min later. These results are the first to show a potent and prolonged inhibitory effect of TRH on evoked glutamate/aspartate release in vitro. These initial studies suggest that exogenous and/or endogenous TRH may function, in part, to modulate excess glutamate release in specific CNS loci. Additional studies are in progress to fully understand the mechanism of this potent effect of TRH and its implication in various CNS disorders. D 2005 Elsevier B.V. All rights reserved.