Effect of streptozotocin-induced diabetes mellitus on serotonin measures of peripheral tissues in rats.

The present study was conducted to examine whether experimental diabetes (streptozotocin-induced) promotes changes in serotonin (5HT) measures of peripheral tissue. Platelet-free plasma 5HT, tryptophan and 5-hydroxyindolacetic acid (5HIAA), whole blood 5HT and renal, liver, intestinal and lung 5HT and 5HIAA levels were measured in rats of four experimental groups: control, diabetic, diabetic+insulin and non-diabetic+insulin. Several serotonin measures were unaltered in all four experimental groups, i.e. plasma, liver and lung 5HT and 5HIAA levels. Whole blood 5HT levels descended about 50% in diabetic rats, then recovered their proper levels after 1 week of insulin therapy. Diabetic animals had a significantly greater intestinal 5HT concentration (+50% versus control), while intestinal 5HIAA levels did not achieve statistical significance despite a -26% decrement in their value. Both renal 5HT and 5HIAA levels were decreased in diabetic animals and recovered with insulin therapy. Peripheral tissue 5HT measures were not varied by insulin administration to non-diabetic animals. The results are consistent with a 5HT release, which is diminished in enterochromaffin cells and enhanced in platelet concomitantly to a minor platelet 5HT uptake, for explaining alterations of plasma/blood 5HT measures in experimental diabetes, and with a diminished synthesis of 5HT for explaining renal changes.