The induction of renal fatty-acid-oxidising enzymes has been investigated following short-term exposure to a group of structurally diverse peroxisome proliferators and compared to the more extensively documented hepatic responses in the rat. There was a marked compound dependence on induction of both cytochrome P-450-IVA1-dependent w-hydroxylation of lauric acid and enzymes of the peroxisomal fatty acid B-oxidation pathway (measured as cyanide-insensitive palmitoyl-CoA oxidation and enoyl-CoA hydratase).Cytochrome P-450 IVAl (or a very closely related isoenzyme in the same gene family) was a major constitutive haemoprotein in rat kidney microsomes and actively supported the o-hydroxylation of lauric acid. This activity was induced 2 -%fold by peroxisome proliferators such as clofibrate, di-(2-ethylhexyl)phthalate, bezafibrate and nafenopin. By using a cDNA probe to the cytochrome P-450 IVAl gene in Northern blot analysis, we have shown that increased renal and hepatic w-hydroxylation of lauric acid, after treatment with peroxisome proliferators is a consequences of a substantial increase in the mRNA coding for this haemoprotein. In addition, programming of an in vitro rabbit reticulocyte translation system with both renal and hepatic RNA resulted in the synthesis of similar (if not identical) cytochrome-P-450-IVAl-related polypeptides. Furthermore, we have provided Western blot evidence that both rat liver and kidney microsomes contain two closely related cytochrome P-450 lVAl polypeptides, the major one characterised by a monomeric molecular mass of 51.5 kDa (identical to authentic, purified hepatic cytochrome P-450 IVA1) and a minor one of 52 kDa. The kidney-supported fatty acid w-hydroxylase activity was refractory to inhibition by a polyclonal antibody to liver cytochrome P -450 IVAl , which may be related to the existence of two closely related (but immunochemically distinct) fatty acid hydroxylases in this tissue.Our studies have also demonstrated that certain of the compounds tested (including clofibrate, bezafibrate and nafenopin) induced renal fatty acid j-oxidation, mirroring the increased w-hydroxylase activity in the endoplasmic reticulum. Our studies have also indicated that the kidney was more refractory to induction of the endoplasmic reticulum and peroxisomal fatty-acid-oxidising enzymes than the liver. Taken collectively, our data is strongly suggestive of a possible linkage of the renal fatty acid oxidative enzymes in these two organelles, a situation that also occurs in the liver. In addition, our studies have provided a possible conceptual framework that may rationalise the decreased susceptibility of the kidney to the toxicity of peroxisome proliferators.The effects of hypolipidaemic agents on rat liver have been extensively studied both in terms of the endoplasmic reticulum changes [l -61 and the associated morphometric and biochemical responses in peroxisomes [7 -91. A recent study has postulated that these adaptive responses are based on a mechanistic interrelationship, whereby chemical c...

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