Reduced venous responsiveness to endothelin-1 but not noradrenaline in hypertensive chronic renal failure

Dialysate composition and hemodialysis hypertension

Dialysis prescriptions have evolved to take advantage of new technology and serve a burgeoning patient population. High-sodium bicarbonate-based dialysate was first formulated in 1982 to enable short, safe, comfortable, high-efficiency hemodialysis (HD). Near-universal adaptation of these high-sodium formulas has virtually eliminated profound dialysis disequilibrium and greatly reduced dialysis discomfort, but has created a syndrome of dialysis salt loading with accentuated postdialysis thirst, interdialytic weight gain, and hypertension. Available technology will soon permit individuals to receive isonatremic dialysis with dialysate customized to the patient's serum sodium activity. Then, rather than choosing between comfortable, safe, high-efficiency dialysis with salt loading; cramps, asthenia, and symptomatic hypotension using low-sodium, high-efficiency rapid HD to control blood pressure (BP) and weight gain; or comfortable, slow, low-efficiency HD with BP control, physicians may be able to minimize symptoms and avoid dialysis salt loading while providing maximum time for rehabilitative activities. The current use of a single sodium activity for all patients ignores the inter- and intraindividual variability in serum sodium activity in our patients. This results in undesired consequences for 20-40% of patients. The application of even more severe salt loading through high-salt sodium modeling only accentuates the long-term problems of excessive thirst, weight gain, and hypertension.

Role of endothelin in regulation of resistance, fluid-exchange, and capacitance functions of the systemic circulation

This article reviews data at the in vivo whole animal and human level. The importance of both flow and pressure recordings and of the methods used to record these variables is emphasized. Exogenous administration of endothelin-1 evokes a transient depressor response mediated by endothelial endothelinB receptors, but the predominate effect of endothelin-1 is a sustained increase in blood pressure resulting from increases in total peripheral resistance. Resistance in the superior mesenteric, renal, and hindquarter vascular beds of animals and forearm resistance in humans is increased. Both endothelinA and, to a lesser extent, endothelinB receptors on vascular smooth muscle mediate the increases in resistance. Endothelin-1 evokes decreases in the precapillary/postcapillary resistance ratio, resulting in increased capillary pressure and net transcapillary filtration. Endothelin-1 evokes increases in mean circulatory filling pressure in animals and in constriction of the human dorsal hand vein. This venoconstrictor activity is mediated primarily through endothelinA and to a lesser extent endothelinB receptors. Endogenously generated endothelin contributes to the hemodynamic effects of angiotensin and vasopressin in certain animal models of hypertension. Antagonists of endothelin evoke modest hemodynamic changes in healthy humans and in some healthy animals, and they decrease vascular resistance dramatically in several salt-sensitive rat models of hypertension and also in some hypertensive human subjects. Thus, endogenously generated ET appears to play a modest role in the healthy organism, but it likely plays a major role in many pathophysiological states as described in companion articles in this issue.

Treatment of the diabetic patient: focus on cardiovascular and renal risk reduction

Diabetes mellitus increases the risk for hypertension and associated cardiovascular diseases, including coronary, cerebrovascular, renal and peripheral vascular disease. The risk for developing cardiovascular disease is increased when both diabetes and hypertension co-exist; in fact, over 11 million Americans have both diabetes and hypertension. These numbers will continue to climb, internationally, since the leading associated risk for diabetes development, obesity, has reached epidemic proportions, globally. Moreover, the frequent association of diabetes with dyslipidemia, as well as coagulation, endothelial, and metabolic abnormalities also aggravates the underlying vascular disease process in patients who possess these comorbid conditions. The renin-angiotensin-aldosterone system (RAS) and arginine vasopressin (AVP) are overactivated in both hypertension and diabetes. Drugs that inhibit this system, such as ACE inhibitors and more recently angiotensin receptor antagonists (ARBs), have proven beneficial effects on the micro- and macrovascular complications of diabetes, especially the kidney. The BRILLIANT study showed that lisinopril reduces microalbuminuria better than CCB therapy. Numerous other long-term studies confirm this association with ACE inhibitors including the HOPE trial. Furthermore, the European Controlled trial of Lisinopril in Insulin-dependent Diabetes (EUCLID) study, showed that lisinopril slowed the progression of renal disease, even in individuals with mild albuminuria. In fact, there are now five appropriately powered randomized placebo-controlled trials to show that both ACE inhibitors and ARBs slow progression of diabetic nephropathy in people with type 2 diabetes. These effects were shown to be better than conventional blood pressure lowering therapy, including dihydropyridine CCBs. In patients with microalbuminuria, ACE inhibitors and ARBs reduce the progression of microalbuminuria to proteinuria and provide a risk reduction of between 38 and 60% for progression to proteinuria. This is important since microalbuminuria is known to be associated with increased vascular permeability and decreased responsiveness to vasodilatory stimuli. Recently, increased AVP levels have been lined to microalbuminuria and hyperfiltration in diabetes. The microvascular and macrovascular benefits of ACE inhibition, ARBs and possible role of AVP antagonists in diabetic patients will be discussed, as will be recommendations for its clinical use.