Dependence of Rabbit External Jugular Vein Vasoreactivity on Segment Size and Location

Abstract

In this study, the dependence of vein segment length, weight, and location on vasore activity was examined. Twenty-four segments from 12 external jugular veins from 6 New Zealand White rabbits were harvested from the proximal (near the thoracic inlet) or distal (near the linguofacial vein/external jugular vein bifurcation) external jugular vein with in vivo lengths of either 3 or 8 mm. Segments were studied in vitro at their resting tension in an organ bath system. The results showed that bradykinin (BK)- and histamine (HIST)-induced maximal active tension 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 = 0.0031). In contrast, BK sensi tivity was dependent on location (proximal segments, -logED₅₀ 7.81 ±0.15 vs distal segments 8.48 ±0.14, P = 0.0006) but was not dependent on size (3 mm segments 8.24 ±0.22 vs 8 mm segments 8.05 ±0.11, P = 0.33) or weight (P = 0.58). HIST sensi tivity, acetylcholine-induced relaxation (endothelium dependent), and sodium nitro prusside-induced relaxation (endothelium independent) were not dependent on segment length, weight, or location. Because significant differences in vasoreactivity exist along the short length of the external jugular vein, vein segment length and location should be rigorously standardized during vasoreactivity experiments. Increased agonist sensitivity from distal to proximal along the length of a vein may provide an additional mechanism for venous return.