Catecholamine release in the locus coeruleus is modified by experimentally induced changes in haemodynamics.

The involvement of catecholaminergic neurons of the locus coeruleus in central cardiovascular control was investigated in the anaesthetized cat. Push-pull cannulae were bilaterally inserted into the LC and the release of noradrenaline and dopamine was determined radioenzymatically in the superfusate. The effects of experimentally induced changes in blood volume and vascular resistance on catecholamine release in the locus coeruleus were studied. Hypervolaemia strongly inhibited the release of noradrenaline in the locus coeruleus. Intravenous infusion of noradrenaline (5 micrograms.kg-1.min-1) elicited a pronounced pressor response which was also associated with a decrease in the release of noradrenaline in the locus coeruleus. Conversely, a fall of blood pressure caused by a controlled haemorrhage enhanced the release of noradrenaline. A profound fall in blood pressure caused by infusion of nitroprusside (8 micrograms.kg-1.min-1) did not modify the release rate of noradrenaline. Dopamine release rate was not significantly influenced by these cardiovascular alterations. The results demonstrate that increases in blood pressure elicited by vascular constriction or hypervolaemia inhibit the release of noradrenaline in the locus coeruleus. Decreases in blood pressure elicited by hypovolaemia enhance the release of noradrenaline, but lowering blood pressure by vasodilatation is ineffective. Hence, the release of endogenous noradrenaline in the locus coeruleus is responsive to haemodynamic signals, thus supporting the suggested integrative role of the locus coeruleus in central cardiovascular control.