The role of endothelin in the age dependent increase in renal vascular resistance in the rat kidney

Endothelin ETA Receptor Blockade With Darusentan Increases Sodium and Potassium Excretion in Aging Rats

This study investigated whether intrarenal endothelin-1(ET-1) contributes to sodium excretion in aged rats. Metabolic function studies were performed in male Wistar rats (3 and 24 months) treated with placebo or the orally active ET(A) receptor antagonist darusentan (20 mg/kg/d) for 4 weeks. Mean arterial pressure was measured using an intra-arterial catheter. Electrolytes, aldosterone levels, renin activity, and angiotensin converting enzyme activity were determined in plasma, and mRNA expression of epithelial sodium channel (ENaC) and Na(+), K(+)-ATPase subunits was measured in the renal cortex and medulla. Aging was associated with a marked decrease in urinary excretion of sodium, chloride, and potassium (all P < 0.001) as well as renin activity (P < 0.05), but had no significant effect on gene expression of ENaC or Na(+), K(+)-ATPase subunits. In aged rats, darusentan treatment increased ion excretion (P < 0.05), reduced cortical gene expression of alphaENaC and alpha(1)-Na(+), K(+)-ATPase (both P < 0.05), and increased plasma aldosterone levels (P < 0.01). These data demonstrate a decrease of sodium and potassium excretion in aged rats, changes that are partly sensitive to ETA receptor blockade. Treatment with darusentan also reduced cortical expression of alphaENaC and alpha(1)-Na(+), K(+)-ATPase and increased plasma aldosterone levels independently of blood pressure, electrolytes, renin activity, or angiotensin converting enzyme activity. These findings may provide new pathogenetic links between aging and sodium sensitivity.

The mechanism of increased renal susceptibility to toxic substances in the elderly. Part I. The role of increased vasoconstriction

The mechanisms of increased susceptibility to nephrotoxins in aging are complex and incompletely understood. It is very important to try to increase our knowledge of them because adults become increasingly vulnerable to nephrotoxic substances, as they grow older. In addition, the percentage of elderly people will increase markedly in the near future, at least in the developed countries. Drugs such as diuretics, laxatives, NSAIDs, aminoglycosides and other nephrotoxic antibiotics, and converting enzyme inhibitors are used a lot by aging people and can produce severe renal problems. Beside drugs, the clinical use of radiocontrast agents also rises in older patients. It seems that the main mechanism of the increased renal susceptibility to toxic substances in the elderly is a disbalance between vasoconstrictor and vasodilator factors (in favor of vasoconstrictor ones). Increased propensity to vasoconstriction (to Ang II, ET and PAF), as well as increased levels of oxidatively modified biomolecules in the elderly, may enhance susceptibility of old kidney to toxic substances. In addition, all mechanisms that influence both mesangial and fibroblast cell proliferation and over-production of extracellular matrix might also be involved in the processes that make the old kidney prone to drug-induced chronic toxic injury.

Acute neutral endopeptidase inhibition is natriuretic in old rats

Neutral endopeptidase 24.11 (NEP) inhibitors prevent breakdown of atrial natriuretic peptide (ANP), and may be useful therapeutically, in sodium overload states as often occurs in the aged. However, age-dependent changes in ANP/NEP may limit the activity of these agents in the elderly. To investigate this we conducted experiments in young, middle aged and old conscious male rats, studied in the baseline euvolemic state and during acute NEP inhibition (NEPI). NEPI produced a marked increase in sodium excretion (>100%) in all groups, regardless of age. A selective, potassium sparing effect was also seen, only in the middle-aged and old rats. Although baseline hemodynamics were affected by age with mean blood pressure, BP, and renal vascular resistance (RVR) being higher in old versus young (131+/-5 vs. 115+/-3 mmHg; P<0.05 and 29+/-3 vs. 20+/-1 mmHg/ml per min per 100 g body weight (BW); P<0.02, respectively); NEPI produced similar mild pressor and significant renal vasoconstrictor effects in all age groups. Despite the tendency of NEPI to reduce renal perfusion, this is an effective method of increasing sodium excretion in all age groups while the potassium sparing actions seen selectively in the older rats may increase the usefulness of NEPI as a diuretic agent for the elderly.