The effect of microvascular pattern alterations on network resistance in spontaneously hypertensive rats.

Structural microvascular rarefaction, defined by a loss of vessels, is a common characteristic of hypertension and has been associated with elevated microvascular resistance. However, determining the causal relationship between microvascular network structure and resistance requires a consideration of all pattern changes throughout a network. The objectives of this study were to determine whether microvascular rarefaction is associated with other network pattern alterations and to evaluate whether pattern alterations in hypertension necessarily contribute to increased microvascular resistance. Mesenteric tissues from age-matched (15-16 weeks) male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were harvested and immunolabeled for PECAM. SHR networks displayed a decreased microvascular area, arteriolar-venular (AV) length, number of AV branches, and number of capillary segments. In addition, SHR networks displayed increased AV connections per network compared to WKY networks. Based on network geometries, resistance per network was calculated using a computational model. For simulations with equal vessel diameter and with relative diameters based on reported intravital measurements, SHR microvascular network resistance was not elevated compared to the WKY level. Our results suggest that microvascular pattern alterations associated with hypertension are more complex than vessel loss, and that these combined alterations do not necessarily lead to elevated resistance.