Pars recta

After administration of mercuric chloride to adult rat kidneys, several changes were found, for example, pars recta of the proximal tubular segment showing fragmentation and disruption of the plasma membrane, basophilic staining, vesiculation and disruption of endoplasmic reticulum and other cytoplasmic membranes, mitochondrial swelling, loss of mitochondrial dense granules and condensation of nuclear chromatin [223-225]. 

The compound damages the pars recta portion of the proximal tubule with the loss of the brush border. The result is renal failure detected as glycosuria, proteinuria, loss of concentrating ability, and reduction in the clearance of inulin, p-aminohippuric acid, and tetraethylammonium ion. 

Hexachlorobutadiene is a nephrotoxic industrial chemical, damaging the pars recta of the proximal tubule. Initial conjugation with GSH is necessary, followed by biliary secretion and catabolism resulting in a cysteine conjugate. The conjugate is reabsorbed and transported to the kidney where it can be concentrated and becomes a substrate for the enzyme p-lyase. This metabolizes it into a reactive thiol, which may react with proteins and other critical macro molecules with mitochondria as the ultimate target. The kidney is sensitive because the metabolite is concentrated by active uptake processes (e.g., OAT 1), which reabsorb the metabolite into the tubular cells. 

Fowler BA, Hook GER, Lucier GW. 1977. Tetrachlorodibenzo-p-dioxin induction of renal microsomal enzyme systems Ultrastructural effects on pars recta (S3) proximal tubule cells of the rat kidney. J Pharmacol Exp Ther 203 712-721. 

S.D. Lenz, and W.W. Carlton, Diphenylamine-induced renal papillary necrosis and necrosis of the pars recta in laboratory rodents. Vet. Pathol. 27 71-178, 1990. 

Gogelein H, Greger R (1986) Na+selective channels in the apical membrane of rabbit late proximal tubules (pars recta). Pfliigers Arch 406 198-203... 

The proximal tubule is the specific target for several antibiotics, mycotoxins, certain antineoplastic drugs, and heavy metals. The proximal tubule can be divided into three discrete segments. The SI segment (pars convoluta) is the initial portion of the proximal convoluted tubule S2 is the transition between the pars convoluta and the pars recta, which consists of the end of the convoluted segment and initial portion of the straight segment and S3 (pars recta)... 

There is convincing evidence that the primary biochemical lesion induced by cisplatin in cancer cells is inhibition of DNA synthesis [27, 28]. The inhibition of DNA synthesis is persistent and occurs at much lower doses than that necessary to inhibit RNA and protein synthesis [29]. Cisplatin binds to two sites in DNA [30] inducing DNA inter- and intrastrand as well as DNA-protein crosshnks [30,31]. What relationship such cisplatin DNA-binding has to renal cytotoxicity is unknown. How such a dechne in DNA synthesis throughout the kidney would explain cell-specific necrosis is problematic but at least two explanations might account for such specificify. First, other cells of fhe kidney repair their DNA lesions while those of the pars recta cannot. Studies in cells whose repair processes are deficient show that cisplatin is especially toxic in them [32] making such a possibility hkely. Second, it may be that the levels of the DNA adducts formed in the pars recta cells are lethal while lower levels in other nephron segments are not. Further studies will be necessary to determine the importance of the reduction in DNA synthesis in renal cytotoxicity. 

Fowler BA. The morphologic effects of dieldrin and methyl mercuric chloride on pars recta segments of rat kidney proximal tubules. Am J Pathol 1972 69 163-74. 

When male Swiss Webster mice were given O.lmgmH of DCVC in drinking water for 37 or 46 weeks, by 26 weeks all the mice developed cortical cataracts. Cytomegaly, nuclear hyperchromatism and multiple nucleoli were noted in the cells of pars recta... 

The cell structure of the pars recta, less complex than that seen in the cells associated with the pars convoluta, is characterized by a decrease in the size and number of mitochondria. As such, the pars recta, in comparison with pars convoluta, is less involved in functions requiring active transport, such as sodium and water reabsorption. 

The ascending thick limb or the pars recta of the distal tubule leads into the distal convoluted tubules or the pars convoluta of the distal tubule. The macula densa is a specialized region corresponding to the initial portion of the pars convoluta of the distal tubule. The two segments of the distal tubule (the pars recta and pars convoluta) are similar morphologically and functionally in terms of active chloride transport and permeability to water. 

Loop of Henie tubule Pars recta oz S69nri6nt Proximal straight tubule (PST) segment ... 

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