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Direct effect of insulin and insulin-like growth factor-I on the secretory activity of rat pancreatic beta cells
Authors:C. F. H. Van Schravendijk  L. Heylen  J. L. Van den Brande  D. G. Pipeleers
Affiliation:(1) Department of Metabolism and Endocrinology, Vrije Universiteit Brussel, Brussels, Belgium;(2) Department of Pediatrics, University of Utrecht, Wilhelmina Children's Hospital, Utrecht, The Netherlands
Abstract:Summary Purified pancreatic Beta cells were labelled with 3H-tyrosine before studying their secretory activity in perifusion. At 1.4 mmol/l glucose, the cells released similar fractions (0.01% per min) of their contents in preformed and in newly formed insulin. At 20 mmol/l glucose plus 10–8 mol/l glucagon, these fractional release rates increased by 16 and 40-fold respectively. The preferential release of newly synthesized as compared to stored insulin is attributable to a heterogeneity in individual cell responses. The secretory responsiveness to glucose plus glucagon was completely suppressed by 10–7 mol/l clonidine. Insulin induced a 20% reduction at 10–6 mol/l, but remained without effect at 10–7 mol/l. Insulin-like growth factor-I provoked a 30% decrease at 5.10–9 mol/l. It is concluded that the type-I insulin-like growth factor receptors on pancreatic Beta cells mediate a suppressive action on the insulin release process. Their high affinity for insulin-like growth factor-I allows physiologic levels of this peptide to participate in the regulation of insulin release. Their low affinity for insulin provides the basis for a minor feedback action by this hormone at concentrations exceeding the normal circulating levels.Part of this study has been presented at the 25th Annual Meeting of the European Association for the Study of Diabetes, Lisbon, Portugal, 1989
Keywords:Insulin release  Beta cells  Insulin-like growth factor-I
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