Increased acetylcholine content induced by adenosine in a sympathetic ganglion and its subsequent mobilization by electrical stimulation

The impact of adenosine on the release of acetylcholine, dopamine, and norepinephrine from the cat carotid body

Exogenously administered adenosine provokes an increase in respiration in both animal models and in man. Administered near the carotid body adenosine increases neural output from the carotid body in rats and cats. Hypoxia has the same effect. Hypoxia also provokes a release of acetylcholine (ACh), dopamine (DA), and norepinephrine (NE) from the carotid body. The present study aimed to determine the effect of exogenous adenosine on the release of ACh, DA, and NE from the carotid bodies of cats. After a recovery period (from surgery) carotid bodies were first incubated for 10 (DA, NE) or 15 (ACh) min in Eppendorf tubes containing 85 microL of a physiological salt solution equilibrated with 40% O2/5% CO2 at 37 degrees C (hyperoxia). At the end of the incubation period the medium was drawn off, and measured for ACh, DA, and NE using HPLC-ECD methods. Next 85 microL of the medium and the tubes were equilibrated with a hypoxic gas mixture (4% O2/5% CO2) and the carotid bodies were incubated for 10 (DA, NE) or 15 (ACh) min, at the end of which the medium was drawn off and measured for ACh, DA, and NE. In the ACh studies there followed a post-hypoxic hyperoxic exposure (40% O2/5% CO2). ACh tubes were then made 100 microM with respect to adenosine, and the hyperoxic, hypoxic, and post-hypoxic hyperoxic challenges were repeated. One of the two DA, NE tubes had the 100 microM adenosine from the start. Adenosine significantly increased the release of ACh, but significantly decreased the hypoxia-induced release of DA. Potential mechanisms for these changes are reviewed.