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- Caye-Thomasen, P, et al.
(författare)
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Depletion of mucosal substance P in acute otitis media
- 2004
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Ingår i: Acta Oto-Laryngologica. - : Informa UK Limited. - 1651-2251 .- 0001-6489. ; 124:7, s. 794-797
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Tidskriftsartikel (refereegranskat)abstract
- Objective-The neuropeptide substance P (SP) is an inducer of neurogenic inflammation and bone resorption in the middle ear. Resorption of the bone tissue structures surrounding the middle ear cavity is a distinct feature of the initial stage of acute otitis media (AOM), which may be due to nerve fiber release of SP. Material and Methods-To investigate possible release of SP in the middle ear mucosa during AOM, we used a well-established rat model of AOM caused by Streptococcus pneumoniae. Following tissue extraction on Days 1, 3 and 6 post-inoculation, the mucosal concentration of SP was measured using a radioimmunoassay. Results-Compared to sham-inoculated control ears, the concentration of SP was significantly reduced on Day 1 and even further reduced on Day 3, whereas partial replenishment was found on Day 6. Conclusion-SP seems to be depleted in the rat middle ear mucosa in the hyperacute phase of AOM. This depletion is followed by replenishment and the concentration of SP approaches its normal level 6 days post-inoculation. The release of SP may be the trigger of the concurrent bone resorption and may further augment the inflammatory response to the bacterial colonization.
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- Gromada, J, et al.
(författare)
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Nateglinide, but not repaglinide, stimulates growth hormone release in rat pituitary cells by inhibition of K+ channels and stimulation of cyclic AMP-dependent exocytosis
- 2002
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Ingår i: European Journal of Endocrinology. - : Oxford University Press (OUP). - 1479-683X .- 0804-4643. ; 147:1, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- Objective: GH causes insulin resistance, impairs glycemic control and increases the risk of vascular diabetic complications. Sulphonylureas stimulate GH secretion and this study was undertaken to investigate the possible stimulatory effect of repaglinide and nateglinide, two novel oral glucose regulators, on critical steps of the stimulus-secretion coupling in single rat somatotrophs. Methods: Patch-clamp techniques were used to record whole-cell ATP-sensitive K+ (K-ATP) and delayed outward K+ currents, membrane potential and Ca2+-dependent exocytosis. GH release was measured from perifused rat somatotrophs. Results: Both nateglinide and repaglinide dose-dependently suppressed K-ATP channel activity with half-maximal inhibition being observed at 413 nM and 13 nM respectively. Both compounds induced action potential firing in the somatotrophs irrespective of whether GH-releasing hormone was present or not. The stimulation of electrical activity by nateglinide, but not repaglinide, was associated with an increased mean duration of the action potentials. The latter effect correlated with a reduction of the delayed outward K+ current, which accounts for action potential repolarization. The latter effect had a K-d of 19 muM but was limited to 38% inhibition. When applied at concentrations similar to those required to block K-ATP channels, nateglinide in addition potentiated Ca2+-evoked exocytosis 3.3-fold (K-d = 3 muM) and stimulated GH release 4.5-fold. The latter effect was not shared by repaglinide. The stimulation of exocytosis by nateglinide was mimicked by cAMP and antagonized by the protein kinase A inhibitor Rp-cAMPS. Conclusion: Nateglinide stimulates GH release by inhibition of plasma membrane K+ channels, elevation of cytoplasmic cAMP levels and stimulation of Ca2+-dependent exocytosis. By contrast, the effect of repaglinide was confined to inhibition of the K-ATP channels.
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