Neogenesis vs. apoptosis as main components of pancreatic beta cell mass changes in glucose-infused normal and mildly diabetic adult rats

We have investigated in adult rats made mildly diabetic by a low dose of st reptozotocin (35 mg/kg; STZ rats) and in nondiabetic rats (ND rats) the mec hanisms leading to adaptive changes in the beta cell mass, during glucose i nfusion and several days after stopping infusion. As early as 24 h of gluco se infusion, the beta cell mass was maximally increased in ND and STZ rats. In both groups, this increase was due mainly to a rapid activation of neog enesis of new endocrine cells rather than to an increase in beta cell proli feration. Seven days after stopping glucose infusion, the beta cell mass re turned to basal values in both groups as a result of stimulation of beta ce ll apoptosis and a decrease in beta cell replication rate. In glucose-infus ed ND rats, changes in the beta cell mass were correlated to insulin secret ion, whereas in STZ rats, insulin secretion in response to glucose was stil l impaired whatever the beta cell mass. In conclusion, the data stress the impressive plasticity of the endocrine pancreas of adult rats. They also sh ow that changes in beta cell mass in ND and STZ rats resulted from a disrup tion in the balance between neogenesis and apoptosis.