Variations in arterioles in spontaneously hypertensive rats. Morphometric analysis of afferent and efferent arterioles.

In the present study, the diameters of afferent and efferent arterioles of kidneys from spontaneously hypertensive rats (SHR) were evaluated and compared with those from Wistar Kyoto rats. (WKY) using a vascular cast model. At 4 weeks of age, the blood pressure was slightly higher in SHR than in WKY (124 +/- 1 vs 116 +/- 7 mmHg, ns). The diameters of afferent arterioles in SHR were smaller than those in WKY (10.3 +/- 0.6 vs 12.3 +/- 0.7 microns, P less than 0.001), whereas the diameters of efferent arterioles were comparable in the two strains. At 20 weeks of age, the blood pressure was markedly elevated in SHR than in WKY (192 +/- 5 vs 140 +/- 4 mmHg, P less than 0.001). The diameters of afferent arterioles in SHR at this age were much smaller than those in WKY (14.3 +/- 0.5 vs 17.1 +/- 0.6 microns, P less than 0.01). The diameters of efferent arterioles in SHR were, however, larger than those in WKY (15.4 +/- 1.2 vs 12.9 +/- 0.4 microns, P less than 0.05). The net effect of these changes in arteriolar size helps to maintain normal intraglomerular pressure and to protect glomeruli from damage due to hypertension.