Pressure within the microvascular bed of the frog mesentery has been recorded continuously with micropressure transducers which have tip diameters ranging between 0.5–5 µ. The mean values of pressure are in the range of those previously reported. The waveform of the pressure pulses in arterioles and metarterioles closely resembles that in the larger arteries. This observation signifies that the vascular walls are considerably stiffer than is generally believed. The stiffness is probably attributable to the constricted vascular smooth muscle.
Transmembrane potential and active tension were measured in isolated segments of turtle aorta and inferior vena cava. Changes in tension were associated with action potentials, but the potentials had a different pattern in the two tissues. When the frequency of the action potentials increased, the contractions summated, resulting in a steadily maintained contraction.
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