Changes in glucose metabolism in submandibular salivary glands of rats after isoproterenol or incisor-tooth amputation

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.

Influence of streptozotocin-induced diabetes on hexokinase activity of rat salivary glands

The influence of diabetes on the enzyme hexokinase (HK) was examined in the salivary glands of rats. Diabetes was induced by an intraperitoneal injection of streptozotocin (60 mg/Kg body weight) in overnight fasted rats (180-200 g). The animals were killed 48 hours and 30 days after the induction of diabetes and the submandibular and parotid salivary glands extracted for use. Hyperglycemia was evaluated by determining the blood sugar. The area occupied by each intralobular component, acini, ducts, total parenchyma and stroma was measured, and no differences were observed compared with control. In the soluble fraction of the submandibular gland, no difference in the specific activity of HK was observed, between the diabetic and control animals, however, the activity per gland and per g of tissue showed lower values than control. The specific activity of the bound form was reduced in the diabetic gland. The results obtained for the parotid gland were different from the submandibular. The specific activity of both the soluble and bound forms were increased in the diabetic animals. The DEAE-cellulose column chromatography of the soluble and bound forms of the enzyme from both glands showed a first peak appearing during the washing of the column and two other peaks were eluted by the gradient. Thus, three isoenzymes in the submandibular and parotid salivary glands for the control and diabetic rats have been found.

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.

Adenine nucleotide changes in submandibular salivary glands of rats following isoproterenol or incisor tooth amputation

Male rats (180-220 g) were injected daily with isoproterenol (2 mg/kg of body weight) for up to 6 days, or their incisor teeth were amputated on every other day for up to six amputations. The animals were subdivided into groups killed 12 or 24 h after the first or last intervention. In the development of sialadenosis caused by isoproterenol, the levels of ATP were greater (13-30%), while those of AMP were lower (13-19%) in the experimental groups. No variation was noted in ADP content. In tooth-amputated animals, only the five and six amputation subgroups showed higher values for ATP (approx. 17%), and ADP (12 and 15%, respectively). The inorganic phosphate level was lower in both experimental groups (between 11-28% for isoproterenol and 13-22% for amputation). Thus isoproterenol caused different metabolic responses in submandibular salivary glands from those induced by incisor amputation.