HYPERTENSION AND THE VASCULATURE - ARTERIOLES AND THE MYOGENIC RESPONSE

Objective: This editorial was invited by the Journal of Hypertension a s one of a series designed to examine our current knowledge of several aspects of the pathophysiology of hypertension. This article consider s small arteries and arterioles. Setting: The conclusion that establis hed hypertension is characterized by a normal cardiac output and a rai sed peripheral resistance represents the integration of findings from haemodynamic studies using a variety of models of the disease examined by several different techniques. In some ways it assumes that all vas cular beds conform to the same pattern of responsiveness. However, giv en the obvious heterogeneity of functions performed by specialized tis sues, the recognized variations in receptor populations and the differ ences in innervation found in the vascular wall throughout the circula tion, this might not be the case. Resistance to blood flow occurs thro ughout the vascular tree, but the majority is found at the level of ar terioles. Upstream small arteries demonstrate growth and remodelling c hanges which result in luminal narrowing, but the exact contribution o f such vessels to resistance is still not known. Perhaps the most inte resting recent finding in this context is that blood pressure can fall immediately after a presser stimulus has been removed, despite the de monstration of such structural changes in small arteries. Furthermore, some whole-animal studies have been reported which fail to show the e xpected vascular amplification when the circulation is stressed in tot al. Conclusion: Viewing the vascular tree as an integrated circuit wit h specialized functions when nourishing specific tissues suggests that when the resistance in one vascular bed increases because of a constr ictor challenge, this might not be representative of the circulation a s a whole: indeed, resistance may fall elsewhere. It is probable that structural changes in small arteries represent the consequence of hype rtension. The pathogenesis of hypertension may reside downstream in ar terioles, where a myogenic response might play a fundamental role.