Myogenic Tone in Isolated Perfused Vessels

In situ studies yield only indirect evidence as to whether non-neurogenic vascular tone results from an intrinsic myogenic tendency of the smooth muscle cell to contract or is due to stimulation of the muscle by some vasoactive humoral influence of the environment. In the current study, small resistance vessels from different vascular beds, from various levels of the arterial tree, and from several species were isolated and perfused with physiological salt solution. Under these conditions the environment is devoid of any vasoactive, in-situ, humoral influence, and tonic contraction would have to be of myogenic origin. Myogenic tone was consistently present in smooth muscle from some vascular beds, whereas it was absent from other beds. Myogenic tone was more prevalent in smaller vessels (50 to 100/A o.d.) than in larger ones (100 to 400/JL o.d.). Significant differences in this property were observed among the species studied. We conclude that, contrary to the properties classically assigned it as a multiunit smooth muscle, most vascular smooth muscle from resistance vessels is intrinsically and spontaneously active.