Differences in effect of 6-hydroxydopamine on the right and left atria from guinea-pig

The effect of chemical sympathectomy by 6-hydroxydopamine (6-OHDA) treatment was studied on guinea-pig atria. 6-OHDA treatment significantly reduced the positive inotropic effect of nicotine and tyramine on the left atrium, while similar treatment on the intact atria and the right atrium showed a decreased response to tyramine but not to nicotine. After 6-OHDA treatment the left atrium but not the right atrium showed supersensitivity to noradrenaline. The 6-OHDA induced reduction of catecholamine content and noradrenaline uptake was less effective on the right atrium in comparison to the left atrium and ventricles. After 6-OHDA treatment, tissue catecholamine fluorescence disappeared from all tissue layers of the left atrium but the number of specific fluorescent nerve terminals of the right atrium was only slightly decreased. These results indicate that adrenergic mechanisms of the right atrium exhibit higher resistance to sympathectomy by 6-OHDA than the left atrium.