Role of the renal microcirculation in antihypertensive therapy

The renal circulation plays a central role in regulating blood pressure and glomerular filtration. To examine the effects of the various classes of antihypertensive agents on the renal microcirculation. Peripheral vascular resistance is generally increased in hypertension, and the microcirculation makes the major contribution to resistance. In the kidney, the preglomerular and postglomerular vessels constrict to protect the glomerular capillary from increased hydrostatic pressure, further increasing peripheral resistance. Because the renal microcirculation adjusts to maintain glomerular filtration and blood flow, antihypertensive agents that can normalize the pressure and blood flow in these vessels may help prevent the long-term consequences of hypertension. Angiotensin-converting enzyme inhibitors directly affect preglomerular and postglomerular resistance, but they further decrease postglomerular resistance. Calcium antagonists selectively decrease preglomerular resistance. The diuretics, vasodilators, alpha blockers, and beta blockers may also cause changes in preglomerular and postglomerular resistance; however, compensatory reflex responses may mitigate their direct effects. Some antihypertensive agents have unique actions on the renal microcirculation that better maintain renal function. A basic understanding of the physiologic action of these agents on the microcirculation may help in their selection.