Karyokinetic reactions in rat kidney proximal convoluted segment epithelium on long-term lead supply with drinking water

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.

Hyperparathyroidism and abnormal 1,25(OH)2 vitamin D3 metabolism in experimental lead intoxication

Clinical evidence points to disturbed calcium metabolism in lead (Pb) intoxication. To further clarify the mechanisms involved, serum levels of 1,25(OH)2D3, receptors for 1,25(OH)2D3 as well as size and ultrastructure of parathyroid glands were examined in Wistar Kyoto rats exposed to 1% lead (Pb) acetate in drinking water for 10 weeks (short-term study) or 0.001-1% Pb acetate for 24 weeks (long-term study). After administration of Pb for 10 weeks, bone Pb was significantly increased (641 +/- 66.9 (SD) vs. 0.648 +/- 0.39 mg kg-1 ash in controls). Total serum calcium and ionized Ca2+ (1.15 +/- 0.031 vs. 1.25 +/- 0.03 mmol l-1) were significantly decreased. Renal function (Ccr) was unchanged, but urinary cAMP excretion and circulating 1,25(OH)2D3 (177 +/- 10.9 vs. 232 +/- 18.9 pmol l-1) were diminished. Specific binding of 1,25(OH)2D3 was increased in parathyroids (Bmax 128 +/- 4.7 vs. 108 +/- 0.6 fmol mg-1 protein) and intestinal muscosa; Bmax failed to adequately rise in response to pretreatment with 1,25(OH)2D3 (2 x 10 ng day-1 for 4 d) in Pb-exposed animals. Receptor characteristics (sedimentation constant, KD, DNA affinity) were unchanged. Parathyroid weight was significantly increased (178 +/- 25 vs. 96 +/- 34 micrograms) with no change of estimated nuclear volume, cell volume or cell ultrastructure. After 24 weeks of Pb exposure, a dose-dependent but non-linear increase of parathyroid weight was noted between 0.001% and 1% Pb in drinking fluid. The present study documents secondary hyperparathyroidism associated with, and presumably caused by, hypocalcaemia and low 1,25(OH)2D3 levels, in experimental Pb intoxication.

Reversible Schwann cell hypertrophy in lead neuropathy

Schwann cell hypertrophy is an early change observed in lead-induced neuropathy in the rat. In order to quantify this cell hypertrophy, a morphometric analysis of Schwann cell cytoplasmic and nuclear areas and their relationship to the cross-sectional area of the associated myelinated fibre was performed. The study was carried out on sural and peroneal nerves from three groups of adult rats. Group I was intoxicated with 4% lead acetate in the drinking water for 6 weeks; group II animals were treated as in group I and then restored to standard laboratory conditions for 30 days; and group III were controls. The results showed that: (a) after 6 weeks of lead exposure, cytoplasmic and nuclear areas were significantly greater in intoxicated, compared with control rats; (b) after 30 days recovery, Schwann cell cytoplasmic and nuclear areas did not differ from control rats.

Suppression of testicular steroidogenesis in rats by the organochlorine insecticide Aldrin

Treatment with Aldrin, an organochlorine insecticide, for 13 and 26 days caused suppression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activities, along with accumulation of cholesterol in the testicular tissues of adult rats. The same treatment also resulted in a reduction in the nuclear diameter of Leydig cells (LCND) and diameter of seminiferous tubules. A decrease in the weight of testes, seminal vesicles and ventral prostate was also noted. HCG administration in the long-term (26 days) treatment restored the steroidogenic enzymes activity and the nuclear diameter of the Leydig cells. It also reduced the accumulation of tissue cholesterol towards the vehicle-injected controls. The inhibition of steroidogenesis in the testes possibly reflects a decrease in pituitary gonadotrophin release after the treatment with Aldrin.