The contribution of the parallel and series elastic components to the dynamic properties of the rat tail artery under two different smooth muscle tones.

The dynamic elastic modulus (Ed) and the coefficient of wall viscosity (ηW) of the tail artery of normotensive rats were determined as functions of the circumferential wall stress under quasistatic and dynamic conditions. The experiments were performed under strong smooth muscle activation induced by norepinephrine, and during relaxation induced by papaverine. The following results were obtained. 1. Ed andηW increase with increasing wall stress. At a given wall stress, Ed is virtually independent of frequency whileηW decreases markedly with increasing frequency. This behaviour ofηW is called thixotropy or pseudoplasticity. 2. In the wall stress range from 5–60 kPa the values of Ed, and in the wall stress range from 60–140 kPa those ofηW obtained under smooth muscle activation and during relaxation are virtually identical. 3. In the relaxed smooth muscle, the phase angles between sinusoidal pressure and radius changes are virtually independent of the mean wall stress at all frequencies. In the low stress range, the phase angles are greater at low frequencies in the activated state than in the relaxed state, decrease with increasing wall stress, and are virtually identical to the values under papaverine at high wall stresses. At high frequencies no dependence of the phase angles on the mean wall stress can be seen.