Neurally mediated and spontaneous release of noradrenaline in the ischemic and reperfused rat heart.

In the perfused (Langendorff) rat heart subjected to global reduction of flow (to 250 microliters/g/min), stimulation of the cardiac sympathetic nerves produces only slightly higher concentrations of endogenous noradrenaline in the venous effluent than occur when such stimulation is performed with flow rates of 4 ml/g/min. This homeostasis is in large part due to the activity of the neuronal uptake system. Complete cessation of flow leads to an early suppression of neurally mediated exocytosis, which persists during the early phase of reperfusion. In the noninnervated heart flow reduction to approximately 250 microliters/g/min for up to 40 min does not produce an overflow of noradrenaline greater than that occurring during the control situation. Reperfusion after 20 and 40 min of flow reduction is, however, associated with a significantly increased overflow of noradrenaline.