Importance of 'cut-end' effects in in vitro artery segments

In order to investigate the consequence of cutting a vascular segment upon its performance in vitro, the contractions of a 4-mm-long segment of ear artery to neurogenic and exogenous norepinephrine (NE) were compared to those of a similar segment cut in half. The active wall tension developed in response to exogenous NE was significantly greater in the 4-mm one-ring segment length (8.50 +/- 0.56 mN/mm) than in the two-ring 2-mm segment lengths (6.64 +/- 0.38 mN/mm) while the EC50 values were the same. The maximum tone (tension) developed at a given frequency of transmural electrical stimulation, expressed as a percentage of maximum tone developed to exogenous NE, was significantly greater (285%) in the one-ring 4-mm segment length than in the two-ring 2-mm segment lengths at the lowest frequency tested (1 Hz) while the tone was approximately equivalent at the higher frequencies (2, 4, 8 Hz). On histological examination, the internal diameter of the artery at the cut ends was less than the remainder of the segment and corresponded with a terminal zone in which the smooth muscle cells, both nuclei and cytoplasm were more deeply stained by hematoxylin and eosin. The transverse diameters of the nuclei and the cells in the end region were reduced so that the muscle cells appeared compressed. Segment 'cut-end' effects would be expected to be relatively more important in shorter ring segment lengths of vessel compared to longer segments.