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.