DEPENDENCE OF RABBIT EXTERNAL JUGULAR-VEIN VASOREACTIVITY ON SEGMENT SIZE AND LOCATION

In this study, the dependence of vein segment length, weight, and loca tion on vasoreactivity was examined. Twenty-four segments from 12 exte rnal jugular veins from 6 New Zealand White rabbits were harvested fro m the proximal (near the thoracic inlet) or distal (near the linguofac ial vein/external jugular vein bifurcation) external jugular vein with in vivo lengths of either 3 or 8 mm. Segments were studied in vitro a t their resting tension in an organ bath system. The results showed th at bradykinin (BK)- and histamine (HIST)-induced maximal active tensio n was dependent on vessel size (BK: 3 mm segments 0.54 +/- 0.10 g vs 8 mm segments 1.42 +/- 0.23 g, P = 0.0003 by paired t test; HIST: 3 mm segments 0.49 +/- 0.15 vs 8 mm segments 1.10 +/- 0.24, P = 0.018) and weight (BK: P < 0.0001 by linear regression; HIST: P = 0.003 1). In co ntrast, BK sensitivity was dependent on location (proximal segments, - logED50 7.81 +/- 0.15 vs distal segments 8.48 +/- 0.14, P = 0.0006) bu t was not dependent on size (3 mm segments 8.24 +/- 0.22 vs 8 mm segme nts 8.05 +/- 0.11, P = 0.33) or weight (P = 0.58). HIST sensitivity, a cetylcholine-induced relaxation (endothelium dependent), and sodium ni tro-prusside-induced relaxation (endothelium independent) were not dep endent on segment length, weight, or location. Because significant dif ferences in vasoreactivity exist along the short length of the externa l jugular vein, vein segment length and location should be rigorously standardized during vasoreactivity experiments. Increased agonist sens itivity from distal to proximal along the length of a vein may provide an additional mechanism for venous return.