Modulation of insulin secretion by leptin

The present study examines the acute effect of leptin (50 nM) on insulin se cretion and on the fractional outflow rates of Ca-45(2+) and Rb-86(+) from pancreatic islets isolated from male lean albino rats. Under a constant phy siological glucose concentration (5.6 mM), the addition of leptin to the pe rifusion medium led to an increment in Ca-45(2+) fractional outflow rate fo llowed by a significant (p < 0.05) increase (26%) in the insulin release. A t low glucose concentration (2.8 mM), leptin also elicited a significant (p < 0.05; 50-60%) increase in insulin secretion. However, under supraphysiol ogical (16.7 mM) glucose concentration, the rapid first-phase insulin secre tion response was abolished. At low glucose levels, islets perifused in the presence of leptin presented a lower Rb-86(+) fractional outflow rate comp ared with perifused controls. In contrast, when glucose was switched to 16. 7 mM, compared with controls, a slight increase in the Rb-86(+) fractional outflow rate was observed instead. These in vitro data provide evidence tha t, by changing Kf fluxes, leptin might modulate insulin secretion from panc reatic islets. (C) 1999 Elsevier Science Inc. All rights reserved.