Effects of denervation induced by 6-hydroxydopamine on cell nucleus activity of arterial and cardiac cells of the dog.

1 Denervation was induced in dogs by 6-hydroxydopamine (6-OHDA) treatment. The effects of this on cell nucleus activity of smooth muscle cells and fibroblasts of the mesenteric artery (main trunk and jejunal branches) and of myocardial cells, fibroblasts and endothelial capillary cells of the heart were studied. 2 Changes in the nucleii or cell size measured with light microscopy morphometric techniques and frequency of nucleoli in myocardial cells were chosen as indices of cell nucleus activity state. 3 Noradrenaline depletion 5 days after initiation of 6-OHDA administration was much more marked in the heart (with a content of 10% of control values) than in the arterial vessels (with a content of 50% of control values). 4 Denervation by 6-OHDA led to an increase in the synthetic activity state of the cell nucleus in all cell types and tissues. 5 Plasma noradrenaline and adrenaline levels were strikingly increased by 6-OHDA treatment. 6 The results strongly support the hypothesis of a nuclear modulating effect of the sympathetic innervation upon the effector cells. The incapacity of high noradrenaline plasma levels to prevent the consequences of sympathetic denervation on the effector cells appears to indicate that in the sympathetic innervation there is a 'trophic factor' which is not identical with noradrenaline.