Carbohydrate, lipid and oxidative metabolism in the sympathetically aneural chick heart

Abstract

Ablation of premigratory trunk neural crest over somites 10 through 20 gives rise to chick hearts which lack sympathetic innervation. Norepinephrine, the neurotransmitter of the postganglionic sympathetic nerves, increases the rate of formation of cyclic AMP (cAMP) in cells. Cyclic AMP the modulator of certain key enzymes of metabolism, was decreased in sympathetically-aneural hearts. Six histochemical assays were used to investigate the metabolic profile of sympathetically aneural hearts as compared to control hearts. NADH-tetrazolium reductase activity (indicator of oxidative metabolism), glyceraldehyde 3-phosphate dehydrogenase activity (indicator of glycolytic rate), beta-hydroxybutyrate dehydrogenase (indicator of beta-oxidation of fatty acids), and oil red 0 assay (neutral lipid content) each demonstrated no difference between aneural and control hearts. Periodic acid-Schiff method for glycogen content, indicated greater stores of glycogen in aneural hearts compared to controls. alpha-Glucan phosphorylase, an enzyme responsible for glycogen hydrolysis, showed less activity in aneural hearts than in controls. The results indicate that the sympathetically aneural heart's metabolism is altered by decreased capability in the maximal rate of glycogen breakdown (decreased phosphorylase Vmax) and subsequent increased storage of the glycogen substrate. Enzymes of other energy transformation pathways were unaltered in the absence of sympathetic nerves.