Differences in functional and structural properties of segments of the rat tail artery.

The investigation of resistance vessels is generally costly and difficult to execute. The present study investigated the diameters and the vascular reactivity of different segments of the rat tail artery (base, middle, and tail end) of 30 male Wister rats (EPM strain) to characterize a conductance or resistance vessel, using a low-cost simple technique. The diameters (mean +/- SEM) of the base and middle segments were 471 +/- 4.97 and 540 +/- 8.39 microm, respectively, the tail end was 253 +/- 2.58 microm. To test reactivity, the whole tail arteries or segments were perfused under constant flow and the reactivity to phenylephrine (PHE; 0.01-300 microg) was evaluated before and after removal of the endothelium or drug administration. The maximal response (Emax) and sensitivity (pED50) to PHE of the whole tail and the base segment increased after endothelium removal or treatment with 100 microM L-NAME, which suggests modulation by nitric oxide. Indomethacin (10 microM) and tetraethylammonium (5 mM) did not change the Emax or pED50 of these segments. PHE and L-NAME increased the pED50 of the middle and the tail end only and indomethacin did not change pED50 or Emax. Tetraethylammonium increased the sensitivity only at the tail end, which suggests a blockade of vasodilator release. Results indicate that the proximal segment of the tail artery possesses a diameter compatible with a conductance vessel, while the tail end has the diameter of a resistance vessel. In addition, the vascular reactivity to PHE in the proximal segment is nitric oxide-dependent, while the tail end is dependent on endothelium-derived hyperpolarizing factor.