Magnesium Modulation of Glucose-Induced Insulin Secretion by the Perfused Rat Pancreas*

Abstract

Increased levels of Mg caused a marked depression of glucose-stimulated insulin secretion at fixed Ca levels, particularly at levels which bracketed the concentration of ultrafiltrable Mg found in normal rat plasma (1.3 meq/l), i.e., increasing Mg from 0.6 to 1.2 meq/l depressed secretion, and increasing Mg from 1.2 to 2.4 meq/l resulted in a further depression. Paradoxically, when Mg was omitted from the perfusing medium, insulin secretion was also depressed. The data strongly suggest that the Ca/Mg ratio is a primary regulator of the insulin secretory process, since a relatively slight alteration of the physiologic ratio of Ca to Mg (.apprx. 2.5) results in a marked alteration of total insulin secretion. Small amounts of Mg are necessary for optimum secretion, possibly reflecting the requirement for Mg in several enzymatic processes. Mg may play an important role in the regulation of insulin secretion by altering the sensitivity of the .beta. cells of the islets of Langerhans to glucose.