Medial changes in arterial spasm induced by L-norepinephrine.

In normal rats, the media of small arteries (0.4--0.2 mm in diameter) previously was shown to contain intracellular vacuoles, identified ultrastructurally as herniations of one smooth muscle cell into another. The hypothesis that intense vasoconstriction would increase the number of such vacuoles has been tested. In the media of the saphenous artery and its distal branch, vasoconstriction induced by L-norepinephrine produced many cell-to-cell hernias within 15 minutes. At 1 day their number was reduced to about 1/10 of the original number. By 7 days the vessel was almost restored to normal. Triple stimulation over 1 day induced more severe changes in the media. These findings suggest that smooth muscle cells are susceptible to damage in the course of their specific function. The experimental data are discussed in relation to medial changes observed in other instances of arterial spasm. Endothelial changes that developed in the same experimental model were described in a previous paper.