[Specific activity and release of norepinephrine in isolated and perfused rabbit hearts under various oxygen...

The incorporation of 3H-tyrosine into norepinephrine of rabbit hearts perfused with Krebs-Henseleit solution containing 11 mM glucose and gassed with 95% O2 - 5% CO2 (control) or 80% O2 - 5% CO2 15% N2 (hypoxic) or 95% N2 - 5% CO2 (anoxic), was studied. In the control hearts a constant specific activity of norepinephrine without any release of catecholamine into coronary effluent was measured after 5, 15, 30, 60 minutes. The hypoxic perfusion while not causing any release of norepinephrine, produced a significant increase in tyrosine incorporation into norepinephrine. The specific activity of norepinephrine and its release into coronary effluent were increased by anoxic perfusion; this effect was most evident when the glucose was replaced with a solution containing 11 mM mannitol. These results suggest that the synthesis of norepinephrine in isolated hearts, lacking of sympathetic innervation, may be affected by different condition of oxygen supply.