Effects of lead on the secretion and disappearance of renin in rabbits

Lead nephrotoxicity and associated disorders: biochemical mechanisms

Lead may exert toxic effects on several organ systems, but those in the kidney are the most insidious. Acute lead nephropathy is characterized by proximal tubular dysfunction with the development of a Fanconi-type syndrome, alterations in mitochondrial structure and the development of cytosolic and nuclear inclusion bodies. Intracellular lead is associated with specific high affinity proteins and can also bind to metallothionein. Chronic lead nephropathy is irreversible and is typically accompanied by interstitial fibrosis, both hyperplasia and atrophy of the tubules, glomerulonephritis and, ultimately, renal failure. In addition, lead produces renal neoplasms in experimental animals. Chronic lead exposure is also implicated in the development of saturnine gout and hypertension. The metal interacts with renal membranes and enzymes and disrupts energy production, calcium metabolism, glucose homeostasis, ion transport processes and the renin-angiotensin system. This review summarizes the biochemical effects of lead on the kidney to understand the mechanisms of lead-induced nephropathy and other associated disorders.

Chronic low-level lead exposure. Its role in the pathogenesis of hypertension

Lead is a common element in the earth's crust, serving useful purposes in industry, but serving no purpose in the human body. Increase in blood pressure is an important public health problem with numerous factors contributing to many facets of the disease. The relationship of lead exposure and increased blood pressure has long been considered, but only recently critically investigated. Reports of subtle changes in calcium metabolism and renal function, as well as in vitro studies examining end-arteriolar smooth muscle contractility, link lead exposure and increased blood pressure. This paper critically examines the evidence associating chronic low-level lead exposure and increased blood pressure. The review focuses on epidemiological, clinical, and toxicological data. The epidemiological evidence is consistent with low-level exposure to lead causing an elevation in blood pressure. The strength of that association, and the dose-response characteristics, are less certain. Individual resistance and susceptibility could affect the degree of blood pressure elevation. The results of animal and in vitro studies are consistent with the epidemiological evidence, and suggest biologically plausible mechanisms for the association. The most probable mechanisms are intracellular perturbations in calcium metabolism mediated by direct lead effects at the end-arteriole, and indirect effects via renal dysfunction. Better indices of lead exposure and lead activity are needed to quantify these effects in humans. New and safer methods of chelating lead suggest interesting approaches for studying the relationship between lead and hypertension. This link could have significant implications in determining what constitutes a 'safe' level of environmental lead exposure, and whether a proportion of essential hypertension could be 'cured' by chelation therapy.

Clearance of renin in unanesthetized rats: effects of chronic lead exposure

These experiments studied the influence of chronic lead exposure on the steady-state clearance of exogenous homologous renin in unanesthetized, unrestrained rats. Relative to time controls (TC), rats chronically exposed to 500 ppm lead in drinking water had significantly elevated basal plasma renin concentrations (PRC) (Pb = 12.0 +/- 1.6 ng/ml/hr, TC = 7.6 +/- 0.8). During the infusion of homologous renin sufficient to increase plasma renin approximately 10-fold, the clearance of renin was not different between the two groups (after 60-min infusion, Pb = 16.1 +/- 1.8 ml/kg/min, TC = 15.9 +/- 1.5). Rats exposed to 1000 ppm lead did not have higher PRCs than time controls (Pb = 10.9 +/- 2.2 TC = 9.2 +/- 1.8). The clearances of renin in these two groups were also not significantly different (Pb = 15.3 +/- 2.8 TC = 18.3 +/- 2.5). Renal renin concentrations were significantly elevated in the 500 ppm rats (Pb = 1426 +/- 110 micrograms/kidney, TC = 1065 +/- 118) consistent with an increased basal renin secretion, but were not elevated in the 1000-ppm rats. There were no significant differences in the clearances of sulfobromophthalein (BSP) between any of the groups. The renin infusion significantly reduced BSP clearance, but did not so equally in all groups. It is concluded that in unanesthetized, unrestrained rats the clearance of renin is not altered by chronic lead exposure of either 500 or 1000 ppm and that increased secretion of renin accounts for the elevated basal PRC observed in rats exposed to the lower dose of lead.