Microvascular tone in a skeletal muscle of spontaneously hypertensive rats.

Abstract

SUMMARY We studied the degree of arteriolar smooth muscle constriction in the spinotrapezius muscle microcirculation of spontaneously hypertensive rats and their normotensive controls, WistarKyoto rats. The constriction was expressed in the form of a nondimensional tone as the difference between steady state and dilated diameter (after papaverine treatment) divided by the dilated diameter. Both animal strains showed on average a progressive increase of tone toward the more distal arterioles, with a peak tone being reached in the transverse arterioles. Tone values in the hypertensive animals were consistently elevated. The number of arterioles that had more than 5% tone (so-called responder arterioles) was higher in the hypertensive animals. These studies suggest that, besides the anatomical adjustments documented earlier in our laboratory in the arteriolar network of this muscle, functional adjustments in the form of an elevated microvascular tone are associated with the elevated resistance in spontaneously hypertensive rats. (Hypertension 9: 164-171, 1987) KEY WORDS • tone skeletal muscle arteriole • spontaneous hypertension • microcirculation O UR earlier studies of the microcirculation dealing with the spontaneous form of hypertension in rats 1 showed that resistance is increased across the hierarchy of precapillary arterioles, as evidenced by the altered pressure-flow relationships in consecutive segments of the spinotrapezius muscle bed. There are, however, insufficient data concerning the factors responsible for such alterations. Previous workers advanced the so-called rarefaction concept of hypertension 2 when they found that there was no statistically significant decrease in the diameter of comparable arterioles in order to account for the above-normal microvascular resistances in spontaneously hypertensive rats (SHR). Experimental data in support of arteriolar rarefaction have been advanced for the cremaster 2 and anterior gracilis muscle preparations 3 of SHR and for the renal form of hypertension. 4 Few of the studies in the literature have estimated microvascular resistance levels on the basis of direct measurements of pressure and flow in the various sections of the network. Our own studies of the problem in

Arteriolar diameter and tissue oxygen tension during muscle contraction in hypertensive rats.

“…The absence of functional rarefaction of small arterioles in the present study cannot be attributed to low vascular tone. Upon abolition of vascular smooth muscle tone with adenosine, the vessels studied in both normal and hypertensive rats dilated proportionately as much or more than arterioles observed in other studies on the spinotrapezius 24 ' N and other rat muscle vascular beds.…”

Nebivolol treatment improves resistant arterial function and reduces ventricular hypertrophy and angiotensin II in spontaneously hypertension rats

“…[13][14][15] It has already been shown that a decrease of only 13% in arteriolar diameter is sufficient to produce an increase in systemic blood pressure of about 50 mmHg. 16 The regression of endothelial function of resistant arteries is generally regarded as an important target of antihypertensive therapy. A single oral dose of nebivolol, 5 mg/day, is indicated for the treatment of essential hypertension.…”

Leukocyte counts and activation in spontaneously hypertensive and normotensive rats.

“…Several proposals have been made in this respect, for example, arterial wall hypertrophy, 19 which could not be confirmed in most vascular regions of the SHR, 20 an elevated tone in the smooth muscle of the arterioles, 21 and structural modifications in the microvascular network. 22 - 23 One of the shortcomings of these proposals has been the failure to provide a link between such vascular modifications and the basic complication in the hypertensive animals (i.e., an accelerated organ injury).…”