Periodic and regulated oscillation of vascular tone, known as vasomotion, is a common feature of small arteries isolated from a variety of peripheral tissues. Vasomotion may be an important physiological mechanism for local regulation of arterial blood flow and has been suggested to be enhanced in conditions of hypertension (Osol & Halpern, 1988). In the present study we report oscillating changes in vessel diameter of pressurised arteries isolated from male Wistar rat mesentery (following humane killing by stunning and cervical dislocation) and human gluteal biopsies (ethical approval having been granted by Central Manchester Healthcare Trust Ethical Committee).

Isolated arteries were mounted on a pressure myograph and constantly superfused with physiological salt solution (pH 7.4, 37 °C). Exposure of rat mesenteric arteries (pressurised to 50 mmHg) to 10 µM phenylephrine resulted in a profound constriction of all vessels studied from 197.5 ± 6.6 to 53.5 ± 4.0 µm (n = 44; mean ± S.E.M.; P < 0.05, Student’s paired t test). This was followed by oscillations in vessel diameter of amplitude 28.6 ± 3.6 µm and frequency 7.3 ± 0.4 oscillations min^-1 in 66 % of cases, which took 28.3 ± 2.7 s to begin following addition of phenylephrine. In all preparations where diameter and global intracellular Ca²⁺ ([Ca²⁺]_i) were measured (by indo-1 ratiometric fluorescence), such phasic mechanical activity was preceded by oscillations in [Ca²⁺]_i (n = 8). Superfusion of mesenteric arteries with 60 mM high K⁺-PSS (n = 25) induced maintained elevation of [Ca²⁺]_i and vessel constriction over a time period of 3 min. Similarly, exposure to 10 µM of the thromboxane analogue U46619 (n = 10) elicited only maintained changes in diameter over a time period of 5 min. In human subcutaneous arteries, however, pressure distension to 60-100 mmHg (n = 84) induced an oscillatory myogenic response in 33 % of cases. Moreover, in 52 % of arteries, exposure to 10 µM noradrenaline also induced regular oscillations in vessel diameter.

These results, in agreement with other vascular studies (Miriel et al. 1999; Peng et al. 2001), suggest important roles for both variations in membrane potential and receptor-coupled IP₃ production in the generation of vasomotion in pressurised rat and human resistance arteries.

This work was supported by The British Heart Foundation.