Kathryn N. Ham

Neoplasia in the rat induced by N-hydroxyphenacetin, a metabolite of phenacetin.

Summary N‐hydroxyphenacetin, a phenacetin metabolite, was fed to rats as a 0.05‐0.5% dietary supplement. After 9 months, tumours of the liver were found in 36 of 64 animals. One animal also developed a renal tumour. No tumours were found in control animals. The findings implicate phenacetin as a carcinogen and suggest that N‐hydroxyphenacetin may be the metabolite responsible.

The nephrotoxicity of p-aminophenol. II. The effect of metabolic inhibitors and inducers.

Inducers and inhibitors of the microsomal mixed function oxidase system have no consistent effect upon the nephrotoxicity of p-aminophenol, or on binding of the compound in vivo to cell protein. p-[ring-3H]Aminophenol was bound in vitro to kidney microsomal protein and to a lesser extent to liver. The binding was enhanced by preincubation of the p-aminophenol in air and inhibited by ascorbate, GSH, N2 and NADPH. These findings indicate that in contrast to paracetamol hepatoxicity which is dependent upon the mixed function oxidase system, that nephrotoxicity of p-aminophenol is dependent upon oxidation to a toxic metabolite by some other pathway. A similar metabolite may be responsible for the nephrotoxic action of phenacetin.

The nephrotoxicity of p-aminophenol. I. The effect on microsomal cytochromes, glutathione and covalent binding in kidney and liver.

p-Aminophenol administration lowered the microsomal cytochrome P-450 and b5 content and decreased the activity of NADPH cytochrome c reductase in kidney, but not in liver. Kidney GSH was depleted to 29% of the control value at 2 h, and only partly restored (50% of control) at 24 h. Liver GSH was transiently decreased, the lowest levels (77% of control) occurring at 30 min. The maximum level of covalently bound radioactivity was at two hours when 16.8% of the total radioactivity in kidney, 1.5% in liver and 3.6% in plasma was protein bound. At this time 81% of the total radioactivity in kidney and 95% of that in the liver was present in the soluble fraction.

Liver and kidney damage induced by N-hydroxyparacetamol.

1. Liver and kidney glutathione are depleted in rats and mice following administration of N-hydroxyparacetamol. 2. Centrilobular hepatic necrosis and necrosis of renal proximal convoluted tubules were also found, the liver lesion predominantly in mice and the renal lesion predominantly in rats. Glutathione depletion was not responsible for this species difference. 3. These results indicate that N-hydroxyparacetamol is the metabolic precursor of the reactive toxic intermediate of paracetamol. They are also relevant to the pathogenesis of the renal damage associated with long term abuse of phenacetin containing compound analgesics.

Nephrotoxicity and Molecular Structure

The nephrotoxicity of a number of aminophenols, quinols and catechols has been assessed from the extent of necrosis of proximal convoluted tubules produced by intravenous injection in rats, and the toxicity correlated with the oxidation-reduction potentials of the compounds.

An Experimental Model of Analgesic-Induced Renal Damage—Some Effects of ρ-Aminophenol on Rat Kidney Mitochondria

1. p-Aminophenol, a known nephrotoxin, has been studied as a model for phenacetin-induced renal damage. 2. Respiration, oxidative phosphorylation and ATPase activity were inhibited in mitochondria isolated from the kidneys of treated rats; this could not be reversed by the addition of exogenous loosely bound cofactors and bovine serum albumin to the assay medium. 3. After treatment the mitochondrial levels of sodium and calcium were increased, potassium decreased and magnesium unaltered. 4. Mitochondria isolated from treated rats showed ultrastructural damage. 5. The results are interpreted to indicate that renal tubular cell mitochondrial injury is important in triggering cortical analgesic renal damage.

The response of newly formed blood vessels in healing wounds to histamine and other permeability factors

&NA; Newly formed blood vessels in the granulation tissue of a healing wound in the rat cremaster muscle are resistant to the permeability‐increasing action of histamine and other agents until 2–3 wk. after their formation. At the stage when newly formed vessels acquire the ability to react to permeability factors, electron microscopic examination still reveals clear evidence of structural immaturity of endothelial cells. The failure of newly formed vessels to respond to permeability factors may be due to absence of contractile protein from the cytoplasm of young endothelial cells. The failure of immature vessels to respond to the type of permeability‐inducing factors normally present in healing wounds may serve a useful purpose in limiting loss of fluid and protein from the surface of extensive wounds.

MACROPHAGES AND GLOMERULAR CRESCENT FORMATION. STUDIES WITH RAT NEPHROTOXIC NEPHRITIS

Summary A model of crescentic glomerulonephritis in the rat was developed, based upon an augmented form of nephrotoxic nephritis. The glomerular lesions were relatively mild, permitting an analysis of the morphologic events in crescent formation to an extent not possible in models in other species in which the sequence of changes is obscured by the severity of the inflammatory process. Monocytes and macrophages accumulated in glomerular capillary lumens and walls. Crescents were composed of cells with ultrastructural features indistinguishable from those of the intracapillary mononuclear cells. The findings support the view that the crescent cells are predominantly composed of macrophages derived from circulating monocytes.

Visceral oedema and increased vascular permeability in early experimental hypertension

&NA; Increased vascular permeability and visceral oedema without significant hypertension or arterial damage was found in clip‐nephrectomized rats dying in the first post‐operative week. Increased vascular permeability was demonstrated by intravenous colloidal carbon labelling, and was restricted to capillaries and venules. Rats surviving the first week became hypertensive, and visceral oedema with predominantly venular and capillary labelling continued, although carbon was now present in arteries also, associated with smooth muscle necrosis. These results suggest that the pressor and permeability effects of renal artery constriction are independent.

The mechanism of the delayed response to X-irradiation of the skin of hairless mice and of rats

&NA; The skin of hairless mice and rats was irradiated with X‐rays and the pattern and extent of the resulting increase in vascular permeability followed in cleared preparations after the in vivo injection of colloidal carbon. Above a threshold dosage of approximately 1500 r in mice and 2000–2500 r in rats, injury consistently produces increased vascular permeability starting 4–5 days after irradiation and reaching a maximum about the 8th–10th day. Leakage is confined to the area of irradiation and occurs both from capillaries and from venules of all sizes. Histological examination shows that the delayed prolonged leakage is accompanied by leucocytic infiltration of the injured area and by damage and necrosis of overlying epidermal cells. Electron microscopic examination reveals alterations in the fine structure of the endothelium of the leaking vessels. These changes are first manifest 4–5 days after injury and reach full intensity a few days later. The changes are similar in type but less severe than those seen after mild thermal injury to the skin. The findings suggest that the delayed response of skin vessels to X‐irradiation, like that to mild thermal injury, is due to direct damage to the vascular wall and not to liberation of an endogenous chemical mediator.