Quinine-induced modifications of insulin release and glucose metabolism by isolated pancreatic islets.

The striking analogies between the processes regulating secretion and contraction led Douglas and Rubin [l] to introduce the term ‘stimulus-secretion coupling’ to parallel the concept of ‘excitation-contraction coupling’ proposed earlier by Sandow [2] . The effects of several alkaloids on muscle contraction have long been recognized and their site and mechanism of action extensively studied [3]. Among these alkaloids, methylxanthines are well-known potentiators of contraction [4] and, more recently, have been shown to increase secretion in various glands, in particular insulin release [5-71. The effects of quinine and of its optical isomer quinidine on contraction are, in some respects, similar to those of methylxanthines, but are more complex, depending on the concentration used and on the type of muscle. As no attention has been paid on possible modifications of secretion by these latter alkaloids, we investigated the action of quinine on isolated islets of Langerhans. In this report, we show that the drug stimulates, potentiates or inhibits insulin release according to the experimental conditions and also alters glucose metabolism by islet cells.