Pilocarpine-induced increases in the activity of 6-phosphofructo-2-kinase and the fructose-2,6-bisphosphate content of rat salivary glands

Lithium Induces Glycogen Accumulation in Salivary Glands of the Rat

Lithium is administered for the treatment of mood and bipolar disorder. The aim of this study was to verify whether treatment with different concentrations of lithium may affect the glycogen metabolism in the salivary glands of the rats when compared with the liver. Mobilization of glycogen in salivary glands is important for the process of secretion. Two sets of experiments were carried out, that is, in the first, the rats received drinking water supplemented with LiCl (38,25 and 12 mM of LiCl for 15 days) and the second experiment was carried out by intraperitoneal injection of LiCl solution (12 mg/kg and 45 mg LiCl/kg body weight) for 3 days. The active form of glycogen phosphorylase was not affected by treatment with LiCl considering the two experiments. The active form of glycogen synthase presented higher activity in the submandibular glands of rats treated with 25 and 38 mM LiCl and in the liver, with 25 mM LiCl. Glycogen level was higher than that of control in the submandibular glands of rats receiving 38 and 12 mM LiCl, in the parotid of rats receiving 25 and 38 mM, and in the liver of rats receiving 12 mM LiCl. The absolute value of glycogen for the submandibular treated with 25 mM LiCl, and the liver treated with 38 mM LiCl, was higher than the control value, although not statistically significant for these tissues. No statistically significant difference was found in the submandibular and parotid salivary glands for protein concentration when comparing experimental and control groups. We concluded that LiCl administered to rats influences the metabolism of glycogen in salivary glands.

Activity, distribution and regulation of phosphofructokinase in salivary gland of rats with streptozotocin-induced diabetes

Although the influence of diabetes on salivary glands is well studied, it still presents conflicting results. In this work, the regulation of the phosphofructokinase-1 enzyme (PFK-1) was studied utilizing the salivary glands of rats. Diabetes was induced by a single intraperitoneal injection of streptozotocin (60 mg/Kg of body weight) in rats (180-200 g). The animals were killed 30 days after the induction of diabetes and the submandibular and parotid salivary glands were used. Hyperglycemia was evaluated by blood sugar determination. The distribution of PFK-1 between the soluble and cytoskeleton fractions, the phosphate content of PFK-1, the content of fructose-2,6-bisphosphate and the activity of the PFK-2 enzyme were determined. The calculated relative glandular weight showed a higher value for the parotid gland in comparison with the control, but not for the submandibular gland. The activity of PFK-1 expressed per gland showed no variation between diabetic and control animals. However, considering the specific activity, the soluble enzyme presented a value 50% higher than that of the control and the cytoskeleton bound form increased by 84% compared to the control. For the parotid gland, no difference in the specific activity between diabetic and control animals was observed. On the other hand, the activity per gland of the soluble enzyme increased in the diabetic animals. The phosphate content of PFK-1 increased in the submandibular and parotid glands of diabetic rats. Both the content of fructose-2,6-bisphosphate and the active form of PFK-2 were reduced in the diabetic glands. In conclusion, the increase in the activity of PFK-1 observed in the salivary glands of rats with streptozotocin-induced diabetes does not seem to be due to its modulator fructose-2,6-bisphosphate.

Altered glycogen metabolism in the submandibular and parotid salivary glands of rats with streptozotocin-induced diabetes

Experimental animal models of diabetes induced either by alloxan or streptozotocin have been used to study aspects of the pathophysiology of this disease. The purpose of this study was to examine the metabolism of glycogen in the submandibular and parotid salivary glands of diabetic rats. Diabetes was induced by an intraperitoneal injection of streptozotocin. Eight weeks after the induction of diabetes, the animals were sacrificed and the submandibular and parotid salivary glands were removed. The glands were analyzed for glycogen concentration, and activities of glycogen synthase and phosphorylase. Although the diabetic rats consumed more food than controls, they had a lower body weight eight weeks after diabetes induction. Glycogen concentration in the submandibular and parotid glands increased by about 27% and 130%, respectively. Glycogen phosphorylase a in the submandibular gland of diabetic rats showed a reduction of between 75% and 68% compared with controls. In parotid glands, phosphorylase a was reduced by between 84% and 79% compared with controls. The increase in the activity of glycogen synthase a (active) varied from 64% to 130% for the submandibular glands and from 75% to 110% for the parotid compared with controls. These results suggest that the diabetic state influences glycogen metabolism in the submandibular and parotid salivary glands of rats.

Regulation of phosphofructokinase-1 on submandibular salivary glands of rats after isoproterenol administration

The purpose of this investigation was to study the effect of isoproterenol (IPR) treatment on the regulation of phosphofructokinase-1 of submandibular salivary glands of rats. The animals were divided into control and experimental groups. In the first set of experiments, the rats received 5 mg of IPR/kg b.w. and were sacrificed at 24 hours after 1, 2, 3 and 4 doses. The content of fructose-2,6-bisphosphate (Fru-2,6-P(2)) and the activity of 6-phosphofructo-2-kinase (PFK-2) (active and total) were determined. The Fru-2,6-P(2) content was found to be reduced and the activity of PFK-2 (active and total) showed differences from the control. The active/total ratio, was higher for the group of one dose sacrificed 12 hours after the agonist injection as compared to the control. In the other groups, there were reductions which varied from 25 to 33%. In the second set of the experiment, the animals were injected with 23.0 mg of IPR/kg b.w. and were sacrificed from 5 up to 720 minutes after the administration of the agonist. After the sacrifice, salivary gland samples were analyzed for Fru-2,6-P(2). Again, a reduction in the metabolite content was observed. Using beta and alpha receptor blockers, it was found that both inhibited only partially the effect of IPR. The purification of PFK-1 up to homogeneity, from submandibular glands of rats which received 5 mg of IPR/mg b.w. as well as from the control, was performed and the Km and state of phosphorylation were determined. Rats from the group sacrificed 12 hours after the injection of the agonist showed the lowest Km for Fru-6-P. Animals which received 3 doses of IPR showed the highest phosphate content/mol of enzyme. Experiments of dephosphorylation of the purified PFK-1 from this latter group revealed that the presence of the phosphate groups influence the kinetic properties of the enzyme.