Streptozotocin-induced diabetes in rats causes neuronal deficits in tyrosine hydroxylase and 5-hydroxytryptamine specific to mesenteric perivascular sympathetic nerves and without loss of nerve fibers.

The aim of this study was to investigate the possibility that inadequate venous return to the heart in diabetes is the result of a neuropathy which affects autonomic nerves supplying the splanchnic vasculature. Mesenteric veins from rats with streptozotocin-induced diabetes were markedly dilated in vivo compared to veins from control animals. Dilation appeared to be the result of loss of muscle tone rather than hypertrophy or hyperplasia of the vessel wall. Using quantification by image analysis and double-labeling immunohistochemistry on mesenteric veins, significant reductions in the density of nerve plexuses staining for 5-hydroxytryptamine (5-HT) and tyrosine hydroxylase (TH) were shown in vessels from diabetic rats compared to controls. No reductions were observed in the density of nerve plexuses stained for the neuronal marker, PGP 9.5, or for substance P (SP), a marker for afferent nerve fibers. These results indicate neurochemical deficits in experimentally induced diabetes which are specific to perivascular noradrenergic nerves and which, within the time-scale of our experiments, do not involve loss of nerve fibers. These deficits may contribute to an increase in venous pooling of blood in the splanchnic vasculature of diabetic rats and thus to inadequate venous return to the heart.