Diabetes
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Comparative Study
Normalization of insulin responses to glucose by overnight infusion of glucagon-like peptide 1 (7-36) amide in patients with NIDDM.
Glucagon-like peptide 1 (GLP-1) is a natural enteric incretin hormone, which is a potent insulin secretogogue in vitro and in vivo in humans. Its effects on overnight glucose concentrations and the specific phases of insulin response to glucose and nonglucose secretogogues in subjects with NIDDM are not known. We compared the effects of overnight intravenous infusion of GLP-1 (7-36) amide with saline infusion, on overnight plasma concentrations of glucose, insulin, and glucagon in eight subjects with NIDDM. ⋯ Reduction of overnight glucose by exogenous insulin did not improve any of the phases of stimulated beta-cell function. Prolonged intravenous infusion of GLP-1 thus significantly lowered overnight glucose concentrations in subjects with NIDDM and improved both basal and stimulated beta-cell function to nondiabetic levels. It may prove to be a useful agent in the reduction of hyperglycemia in NIDDM.
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Randomized Controlled Trial Multicenter Study Clinical Trial
The absence of a glycemic threshold for the development of long-term complications: the perspective of the Diabetes Control and Complications Trial.
The Diabetes Control and Complications Trial (DCCT) demonstrated a reduction in the development and progression of the long-term complications of IDDM with intensive therapy aimed at achieving glycemic control as close to the nondiabetic range as possible. The DCCT subsequently showed that the total lifetime exposure to glycemia was the principal determinant of the risk of retinopathy and that there was a continuous nonlinear relationship between this risk and the mean level of HbA1c (DCCT Research Group, Diabetes 44:968-993, 1995). In contrast, other authors, based on a retrospective study (Krolewski et al., N Engl J Med 332:1251-1255, 1995), have suggested that a glycemic threshold for microabuminuria and for retinopathy exists at an HbA1c level of approximately 8%, below which there is no further appreciable reduction in risk. ⋯ These extensive prospective DCCT data do not support the conjecture that a glycemic threshold for the development of complications exists at an HbA1c of 8% or that an HbA1c goal of 8% is maximally beneficial. In the DCCT, as HbA1c was reduced below 8% there were continuing relative reductions in the risk of complications, whereas there was a slower rate of increase in the risk of hypoglycemia. Therefore, the DCCT continues to recommend implementation of intensive therapy with the goal of achieving normal glycemia as early as possible in as many IDDM patients as is safely possible.
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Endothelin-1 (ET) is a potent vasoconstrictor of vasa nervorum, the vascular supply of peripheral nerve trunks, that may, through elevated circulating levels, promote microangiopathy in human diabetes patients. In previous work, we observed that sciatic nerve trunks of rats exposed to epineurial ET developed transient dose-dependent endoneurial ischemia that might be associated with reversible motor conduction block. In the present study, we explored the possibility that ET ischemia might selectively damage axons of diabetic nerve trunks. ⋯ Histological studies confirmed the presence of severe axonal degeneration in diabetic sciatic nerves exposed to ET. Part of the susceptibility to ET in diabetes was accounted for by more intense and prolonged vasoconstriction. Diabetic nerves are selectively susceptible to ET-mediated ischemia.
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Rat pancreatic alpha- and beta-cells are critically dependent on hormonal signals generating cyclic AMP (cAMP) as a synergistic messenger for nutrient-induced hormone release. Several peptides of the glucagon-secretin family have been proposed as physiological ligands for cAMP production in beta-cells, but their relative importance for islet function is still unknown. The present study shows expression at the RNA level in beta-cells of receptors for glucagon, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide I(7-36) amide (GLP-I), while RNA from islet alpha-cells hybridized only with GIP receptor cDNA. ⋯ Maximal stimulation of cAMP production was comparable for the three peptides. In purified alpha-cells, 1 nmol/l GLP-I failed to increase cAMP levels, while 10 pmol/l to 10 nmol/l GIP exerted similar stimulatory effects as in beta-cells. In conclusion, these data show that stimulation of glucagon, GLP-I, and GIP receptors in rat beta-cells causes cAMP production required for insulin release, while adenylate cyclase in alpha-cells is positively regulated by GIP.