Antihypertensive drug therapy and arrhythmia risk

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Hypertension in the elderly

Based on the best evidence we have currently, treating the elderly patient with diastolic hypertension will significantly decrease the risk of stroke. While the evidence for decreasing the risks of coronary disease, congestive heart failure, renal insufficiency, or total mortality is not present, such evidence does exist in younger patients with more severe hypertension. Thus, it is of benefit to reduce the blood pressure in hypertensive older patients. There is some evidence that the elderly may not be more susceptible to side effects of antihypertensive medications than younger populations. However, it is certainly reasonable to attempt blood pressure control by nonpharmacologic means prior to drug treatment. Demographic considerations may affect the choice of medication; in general the stepped-care approach will provide effective management of elevated blood pressure in this population.

Cardiovascular risks: new insights from Framingham

Although cardiovascular disease remains the leading cause of death in the United States, its incidence has decreased steadily during the past 20 years. This trend is largely attributable to improved detection and management of cardiovascular risk factors. The pioneering work of the Framingham Heart Study, which has followed subjects since the late 1940s, has helped shed light on the risks conferred by factors such as advancing age, hypertension, smoking, elevated serum cholesterol, diabetes, left ventricular hypertrophy, and obesity. As a result of this ongoing investigation, clinicians have gained a better understanding of the ways in which cardiovascular risks can be modified so that mortality rates will hopefully continue to decline.