Nicotine and carbon monoxide: effects on the isolated rat heart

We studied the combined effects of carbon monoxide (CO) and nicotine on the performance of the isolated rat heart. Hearts were removed from laboratory rats and perfused through the aorta with 95% O2-5% CO2 (oxygenated) Krebs-Henseleit solution (KHs). After 30 min, the perfusate was switched rapidly to one of three solutions: KHs containing 10% CO-85% O2-5% CO2 (CO), 10 micrograms/ml nicotine (Nic), or CO combined with nicotine (CO + Nic). KHs containing CO increased coronary flow by 41% without affecting heart rate or pulse pressure. Coronary flow returned to control values during recovery in oxygenated KHs. KHs containing Nic decreased heart rate by 20% and coronary flow by 28%. Pulse pressure was unaffected. Both heart rate and coronary flow returned towards control values during recovery in oxygenated KHs. KHs containing CO + Nic decreased heart rate 16% but stimulated coronary flow 13%. Heart rate returned towards control values during recovery; however, coronary flow, which declined to control values after 8 min, continued to decrease during recovery. These results indicate that the separate effects of CO and Nic on coronary flow in the isolated rat heart are opposing and reversible, but that the decrease they produce in combination is irreversible.