Rendell M S, Finnegan M F, Pisarri T, Healy J C, Lind A, Milliken B K, Finney D E, Bonner R F
Creighton Diabetes Centre, Creighton University School of Medicine, Omaha, NE 68131, USA.
Comp Biochem Physiol A Mol Integr Physiol. 1999 Apr;122(4):399-406. doi: 10.1016/s1095-6433(99)00022-7.
The Spontaneously Hypertensive rat (SHR) and its non-hypertensive companion strain, the Wistar-Kyoto (WKY) rat, provide an excellent comparative model to permit study of the differential properties of cutaneous microvascular beds. We explored the possibility that chronically elevated vascular pressures in the SHR rat might affect the microvascular constitution of the skin. We measured skin blood flow at the back and at the paw of a group of 20-week-old WKY rats and a contrast group of SHR rats. We then performed skin biopsies at these two locations and used the NIH Image program to count and measure the size of capillaries, arterioles, and venules. We also determined microvascular density as percentage of total tissue area. At basal temperature, skin blood flow was similar in the two rat strains at both the back and paw. Heat induced vasodilatation resulted in a 50% increase in blood flow at the back, reaching the same level in the two rat groups. However, at the paw site, thermal stimulation resulted in significantly greater flow (39.3 +/- 3.1 ml/100 gm tissue per min) in the SHR rats than the WKY rats (28.6 +/- 1.9 ml/100 gm tissue per min, P < 0.05). The ratio of systemic arterial pressure to skin blood flow was computed as an index of vascular resistance to flow. At basal temperature, this index was 50% greater for the SHR rats at both skin sites. At 44 degrees C, the resistance index decreased at both sites in both rat groups but was still approximately 50% higher at the back of the SHR than the WKY rats. In contrast, the resistance index at 44 degrees C at the paw site fell to the same level in both the SHR and WKY rats. There were twice as many capillaries at the back of the WKY rats than at the back of the SHR rats (9.2 +/- 2.0 per mm2 vs. 4.7 +/- 1.2 per mm2, P < 0.05). Expressed as a percentage of total tissue area, the capillary density at the back in the WKY rats was 0.064 +/- 0.010% as compared to 0.034 +/- 0.008% in the SHR rats (P < 0.05). There were five times more arterioles at the paw compared to the back in both rat groups with no significant difference between the groups. We measured the diameter of the lumen and the thickness of the wall of each arteriole and computed their ratio as an index of possible media hypertrophy. There were minimal differences seen in these parameters between the two rat groups at the back and paw sites. The venular density was significantly higher at the paw than at the back in both rat groups with no significant difference between them. Reduced capillary density at the back of the SHR rats may be a developmental adaptation to high blood pressure. Such a reduction in the pathways of blood flow may help account for increased flow resistance at that site, independent of arteriolar vasoconstriction.
自发性高血压大鼠（SHR）及其非高血压对照品系Wistar-Kyoto（WKY）大鼠，为研究皮肤微血管床的差异特性提供了一个极佳的比较模型。我们探讨了SHR大鼠长期升高的血管压力可能影响皮肤微血管构成的可能性。我们测量了一组20周龄WKY大鼠以及一组对照SHR大鼠背部和爪部的皮肤血流量。然后我们在这两个部位进行皮肤活检，并使用美国国立卫生研究院图像程序来计数和测量毛细血管、小动脉和小静脉的大小。我们还将微血管密度确定为总组织面积的百分比。在基础温度下，两种大鼠品系在背部和爪部的皮肤血流量相似。热诱导血管舒张导致背部血流量增加50%，在两组大鼠中达到相同水平。然而，在爪部，热刺激导致SHR大鼠的血流量（39.3±3.1毫升/100克组织每分钟）显著高于WKY大鼠（28.6±1.9毫升/100克组织每分钟，P<0.05）。计算全身动脉压与皮肤血流量的比值作为血流血管阻力指数。在基础温度下，该指数在两个皮肤部位的SHR大鼠中均高出50%。在44℃时，两组大鼠在两个部位的阻力指数均下降，但SHR大鼠背部的阻力指数仍比WKY大鼠高出约50%。相比之下，在44℃时，爪部的阻力指数在SHR和WKY大鼠中降至相同水平。WKY大鼠背部的毛细血管数量是SHR大鼠背部的两倍（9.2±2.0个/平方毫米对4.7±1.2个/平方毫米，P<0.05）。以总组织面积的百分比表示，WKY大鼠背部的毛细血管密度为0.064±0.010%，而SHR大鼠为0.034±0.008%（P<0.05）。在两个大鼠组中，爪部的小动脉数量均比背部多五倍，两组之间无显著差异。我们测量了每个小动脉的管腔直径和管壁厚度，并计算它们的比值作为可能的中膜肥厚指数。在两个大鼠组的背部和爪部部位，这些参数之间的差异极小。在两个大鼠组中，爪部的小静脉密度均显著高于背部，两组之间无显著差异。SHR大鼠背部毛细血管密度降低可能是对高血压的一种发育适应性变化。这种血流途径的减少可能有助于解释该部位血流阻力增加的原因，而与小动脉血管收缩无关。
