Micropressure-flow relationships in a skeletal muscle of spontaneously hypertensive rats.

Abstract

Direct intravital microscopy was used to analyze microcirculatory changes in the exteriorized spinotrapezius muscle of spontaneously hypertensive rats (SHR). The animals were anesthetized with a mixture of chloralose-urethane, and measurements were made of pressure, flow and resistance in vessels ranging in size from 50-5 .mu.m. The vascular changes in SHR were compared with matched Wistar-Kyoto (WKY) strain animals for both young (5-6 wk old) and mature (12-13 wk) rats. Distinctive changes in the distribution and levels of pressure, flow and resistance were seen in the entire microvascular network during both stages of the syndrome. There was no significant increase in the resistance of the conduit arteries just proximal to the muscle proper. Blood pressure in hypertensives was brought down to normal and even below normal at the level of the capillaries and postcapillaries irrespective of the height of the pressure in the major artery supplying the muscle. The greater drop in pressure across the arteriolar branchings of the hypertensives was seen as early as at 5-6 wk of age; this difference is much more striking in 12-13 wk-old mature hypertensives. The reduction in pressure was proportionately greatest in the region of the smallest (10-15 .mu.m) precapillaries of hypertensives. Resistance values were below normal in the confluent capillaries and postcapillaries in both young and mature hypertensives. Volumetric flow, which was marginally higher throughout the arteriolar branchings, fell below normal on the postcapillary side. Since an increased resistance developed at an early age (5-6 wk) in all of the microvessels on the precapillary side, hypertension may be associated with a generalized effect on the muscular arterioles below 30 .mu.m, an effect that becomes more pronounced with time and at 12-13 wk begins to involve larger size arterioles (30-40 .mu.m wide).