Neuropeptide Y is released together with noradrenaline from the human heart during exercise and hypoxia

The myocardial release of neuropeptide Y-like immunoreactivity (NPY-LI) and noradrenaline (NA) during exercise with and without arterial hypoxia was measured in 18 healthy men by arterial (a) and coronary sinus (cs) catheterization. Exercise was performed in the supine position on a cycle ergometer at a load, selected to produce a heart rate during air breathing of 120 beats min-1. Coronary sinus blood flow (CSBF) was measured and a and cs samples for NPY-LI, NA, oxygen and lactate analyses were taken at rest and after 6 min exercise. The inspiratory gas was then switched to 15% (n = 8) or 12% (n = 10) oxygen in nitrogen, exercise continued at the same load and measurements repeated after 6 min. At rest no significant release and during normoxic exercise a very small myocardial release of NPY-LI and NA was detected. During hypoxia compared to normoxia the cardiac NPY-LI release increased four-fold and the NA net release doubled at the same time as the arterial NPY-LI remained unaltered or only slightly increased. Both the NPY-LI and the NA net release from the heart correlated with the heart rate and the arterial but not the cs oxygen tension. The NPY-LI release was correlated with the NA net release. The findings suggest that arterial hypoxia stimulates cardiac NPY together with NA release which derives from local sympathetic nerves. The release from the heart seems to be greater than from other tissues.