Epidermal growth factor secretion by submandibular glands is not perturbed in the early phase of streptozotocin-induced diabetes in mice.

In rodents, diabetes mellitus is accompanied by a decreased concentration of epidermal growth factor (EGF) in plasma and urine and by a reduced number of EGF receptors on the surface of target cells. A combination of these two abnormalities may reduce the effects of EGF and could be implicated in some complications of diabetes. The aim of the present work was to investigate the possible implication of the major source of EGF in the organism, the submandibular glands, upon the reduced EGF concentration in blood and urine. Firstly, we measured the content of mice submandibular gland EGF by radioimmunoassay and by morphometric determinations of the relative volume occupied by granular convoluted tubules in the gland and by the EGF-containing granules in the cells at the light and electron microscopical levels respectively. We found no differences in the EGF content of submandibular glands of streptozotocin-treated diabetic animals compared to control ones. Secondly, we estimated stimulus-secretion coupling by EGF-secreting cells, present in an enriched preparation of granular convoluted tubules (GCT) perifused in thermoregulated chambers. Phenylephrine was the only agent tested that was capable of stimulating EGF secretion. The stimulation was dose-dependent and similar in streptozotocin-diabetic and control mice. Thus, the EGF deficiency observed in diabetic mice is related neither to a defect of EGF content in the submandibular glands nor to an abnormal EGF secretion by the glands.