This article has analyzed the pathogenesis of sodium and water retention in several circumstances. The initiator of retention has been proposed to be either a fall in cardiac output (e.g., low-output cardiac failure and vasoconstrictor hypovolemic nephrotic syndrome) or peripheral arterial vasodilatation (e.g., high-output cardiac failure, cirrhosis, arteriovenous fistula, and pregnancy). In the only state discussed, in which the kidney is diseased and not merely responding to extrarenal reflexes--i.e., nephrotic syndrome--intrarenal mechanisms may predominate and lead to expansion of the arterial vascular tree and suppression of the renin-angiotensin-aldosterone system (i.e., hypervolemic nephrotic syndrome). Otherwise, when kidneys are healthy, either a fall in cardiac output or peripheral arterial vasodilatation may diminish arterial vascular filling and thereby initiate a series of hemodynamic and hormonal events that result in renal sodium and water retention (Fig. 7). Finally, the approach presented in this article should be considered to be a vantage point from which to evaluate states of sodium and water retention, but not to be an exclusive position.

Thousands of studies have been conducted of the functioning of the many neurotransmitter systems in order to explore the biologic basis of major depressive disorder. Instead of reviewing this literature exhaustively, we have attempted to propose a model that accommodates the clinical observation that chronic stress early in life in vulnerable persons predisposes them to major depression with contemporary observations of the potential consequences of repeated central nervous system exposure to effectors of the stress response. This model accords with current clinical judgment that major depression is best treated with a combination of psychopharmacologic agents and psychotherapy. Accordingly, whereas psychopharmacologic intervention may be required to resolve an active episode of major depression and to prevent recurrences, psychotherapy may be equally important to lessen the burden of stress imposed by intense inner conflict and counterproductive defenses.

The diversity of its causes, the unpredictability of its clinical course, and our expanding knowledge of the conditions that may exacerbate or retard its progression suggest that glomerular sclerosis cannot be attributed to a single aberration in glomerular physiology. Nonetheless, the welter of clinical and experimental observations is beginning to yield a pattern. Agents or conditions injurious to glomerular epithelium tend to cause glomerular sclerosis. Agents or conditions that induce short-term or long-term activation of mesangial cells may lead to glomerular sclerosis. Indeed, one contribution of the healthy epithelium may be to serve as a tonic inhibitor of the intraglomerular processes arising from mesangial-cell activation. Long-term activation of the mesangium is associated with the proliferation and infiltration of cells and with the expansion of the mesangial matrix--the antecedents of sclerosis. We anticipate that different diseases associated with glomerular sclerosis will be found to depend to varying extents on these two potential mechanisms of sclerosis. Beyond a certain threshold of glomerular injury, glomerular diseases share an additional factor: the capacity of both intrinsic cells and infiltrating cells to alter the microenvironment of the glomerulus so that sclerosis progresses inexorably long after the disappearance of the initiating insult. Several potential risk factors may contribute to the progression of chronic renal disease. These factors include systemic hypertension, proteinuria, hyperlipidemia, high protein intake, and probably conditions that lead to glomerular hypertrophy. Interventions designed to minimize the potential contribution of these factors to the progression of renal insufficiency may halt or slow the loss of function of the kidney. Clinical trials designed to examine the effects of these factors on the progressive course of renal insufficiency will help to establish their role and relative importance in humans.

As a long-term dialysis therapy, CAPD has attractive features for use in children (in whom access to the circulation and immobility are often problems), adults in whom blood access is difficult, patients with diabetes, patients prone to hypotension, and patients seeking independence from a machine or medical facility. CAPD and related procedures are still evolving and improving. Efforts to reduce the rates of peritonitis are ongoing and should decrease the rates of treatment dropout and increase the use of this alternative method of dialysis. Continued research toward improvements in catheter configuration and connection devices and the tailoring of technique to meet the particular needs of patients have made peritoneal dialysis an acceptable replacement therapy in patients with end-stage renal disease. Neither peritoneal dialysis nor hemodialysis is the superior long-term dialysis therapy for all patients; the choice depends on numerous medical, social, geographic, and life-style considerations.