Extracellular calcium and glucose-induced insulin release during fasting in isolated perfused rat pancreas

The effects of different concentrations of Ca2+ (2.5 or 7.5 mM) upon the kinetic and dynamic aspects of glucose-induced insulin release were investigated in the isolated perfused pancreas of fed and 4-day fasted rats. The curve relating the rate of insulin release to the glucose concentrations (2.75-33.4 mM) showed a sigmoidal shape and was similar at both Ca2+ concentrations in the fed state. Pancreas of fasted animals showed a diminished insulin secretion and the kinetic pattern was linear throughout the whole range of glucose concentrations studied at 2.5 mM Ca2+. Perfusion of pancreas from fasted rats with glucose at 7.5 mM Ca2+ resulted in an increase of insulin secretion but the kinetic behaviour continued to be linear. In contrast, pancreas of 4-day fasted plus 2-day refed rats showed a kinetic of glucose-induced insulin secretion with the cooperative mechanisms observed in fed control animals. It is concluded that changes in Ca2+ utilization by the pancreatic beta cell play little role in the decreased insulin release observed in the fasted state.