Paracrine interactions within islets of Langerhans.

Glucose supply fluctuates between meal and fasting periods and its consumption by the body varies greatly depending on bodily metabolism. Pancreatic islets of Langerhans secrete various endocrine hormones including insulin and glucagon to keep blood glucose level relatively constant. Additionally, islet hormones regulate activity of neighboring cells as local autocrine or paracrine modulators. Moreover, islet cells release neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) to gain more precise regulation of hormones release kinetics. Excitatory glutamate is co-released with glucagon from α-cells and activates glutamate receptors in the neighboring cells. GABA released from β-cells was shown to inhibit α-cells but to activate β-cells by acting GABA(A) receptors. This review summarizes the recent progress in understanding the paracrine/autocrine interactions in islets.