Arterial vasomotion and its relation to intraluminal pressure were investigated in vitro in isolated rat arteries. Femoral arteries (mean diameter = 768.2 +/- 25 microns, n = 5) and mesenteric arteries (mean diameter = 393.4 +/- 32 microns, n = 5) were used in this study. Arterial segments were excised, mounted on microcannulas and perfused with Tyrode's solution at a constant flow (100 microliters/min). After equilibration, intraluminal pressure was stepwise changed from 0 to 120 mm Hg. The changes in the outer diameter of the vessels were measured continuously over a period of 4 h after the equilibration. Vasomotion was induced by constrictor agonists (norepinephrine 10(-6) M for mesenteric arteries and norepinephrine 10(-6) M + Bay K8644 10(-7) M for femoral arteries) and was maintained only in the presence of the above-mentioned drugs. Both vasomotion magnitude and frequency are modulated by pressure. Vasomotion frequency increases with pressure increase. When intraluminal pressure varied between 0 and 120 mm Hg, vasomotion frequency varied between 0.19 and 0.49 Hz for mesenteric arteries and between 0.04 and 0.23 Hz for femoral arteries. Thus, vasomotion frequency differed clearly between the two vessel types. Vasomotion amplitude shows a biphasic relationship with a maximum occurring at about 40 mm Hg for mesenteric arteries and 50 mm Hg for femoral arteries. Based on these findings, it is hypothesized that vasomotion amplitude relates to the active mechanical properties of the artery and, in particular, to its contractile capacity.