Enzyme histochemistry of rat folic acid nephropathy.

One hour after a single i.v. dose of 250 mg/kg folic acid, the straight portion of distal tubules in the outer medulla of rat kidneys showed a distinct reduction in succinate dehydrogenase, NADH2-diaphorase, glutamate dehydrogenase, cytochrome oxydase, Na+/K+-ATPase, and acid phosphatase activity. In contrast, the proximal tubules exhibited only a reduction in glutamate dehydrogenase and alkaline phosphatase activity. At this time the straight portion of the distal tubules, whose enzyme activity had changed, showed partly regressive epithelial changes. 24 hours after folic acid administration an even greater reduction in enzyme activity had occurred in the straight portion of distal tubules; these structures also became dilated. The adjacent collecting tubules and the corresponding proximal tubules were also severely dilated, the proximal tubules showing a loss in enzyme acitivities similar to those observed in the distal tubules. 48 hours after folic acid administration the changes largely resembled those observed after 24 hours, but were more pronounced. At this time a tubular regeneration was observed. 72 hours after folic administration extensive normalization of the histological and histochemical changes had occured. It is postulated that a disturbance of the hairpin counter-current mechanism occurs as a result of a direct, concentration-dependent effect of folic acid on the enzymes of the energy supplying metabolism. A dilation in the region of the loop of Henle and the collecting tubules occurs subsequently.     

The occurrence of lipid droplets in the proximal and distal tubules of the rat kidney after folic acid treatment.

Folic acid in high doses gives rise to an accumulation of lipid droplets in the kidney in addition to other changes in the epithelial of both proximal and distal tubules. With the administration of methionine a decrease of lipid droplets and an improvement of the structures of most of the membranes and mitochrondria are observed. These findings have been discussed in regard to the theory of the "chemically induced hyperplasia of the kidneys" related to folic acid.     

Uric acid excretion by the rat kidney.

The renal excretion of uric acid was studied in nondiuretic (ND) male Wistar rats and in the same animals subsequently made diuretic (D) by the infusion of hypertonic saline. Clearances of endogenous urate and of inulin, determined chemically, were compared with the simultaneous clearance of 14C infused as [6(-14)C]urate or [2(-14)C]urate. In rats infused with [6(-14)C]urate the isotope/inulin clearance ratios were 0.29 +/- 0.09 (ND) and 0.31 +/- 0.11 (D) ml/min; the simultaneous urate (chemical)/inulin ratios were 0.21 +/- 0.07 (ND) and 0.24 +/- 0.08 (D) ml/min. In rats infused with [2(-14)C]urate the isotope/inulin clearance ratios were 1.02 +/- 0.5 (ND) and 1.13 +/- 0.9 ml/min (D); the simultaneous urate (chemical)/inulin clearance ratios were much lower-0.19 +/- 0.09 (ND) and 0.32 +/- 0.19 (D) ml/min. Thin-layer chromatography of urine after [6(-14)C]urate inl uric acid. In contrast, a similar analysis of urinary radioactivity after [2(-14)C]urate infusion revealed that more than 70% of the 14C was excreted as allantoin and not as uric acid.     

The kidney in streptozotocin diabetic rats. Morphologic, ultrastructural, and function studies.

In order to study the nephropathy associated with experimental streptozotocin diabetes, serila morphologic, ultrastructural, immunohistologic, and functional studies were done in diabetic Lewis rats to study the course of the nephropathy. Early in the course of diabetes, these animals developed an increase in mesangial matrix, with electron-dense material, IgG, and C3 in the mesangium. These alterations were progressive. Mesangial bars, proximal tubular vacuolization, and myeloid bodies were also present. Progressive increase in protein excretion and increase in creatinine clearance were observed. Hyperglycemia was accompanied by weight loss, persistent glycosuris, hyperphosphaturia, and hypercalcuria. Urinary glomerular basement membrane-like protein and major urinary protein were decreased. Normal age-matched controls showed no abnormalities. Some of the changes observed in diabetic rats are present in human diabetes.     

Virus-induced animal model of osteosarcoma in the rat: Morphologic and biochemical studies.

Osteosarcomas were produced by the intratibial inoculation of New Zealand black rats with Moloney sarcoma virus (MSV) at 1 day and 4 days of age. Radiographic evidence of osteosarcoma development was first demonstrated at 10 to 15 days postinoculation in both groups. Subsequent radiographic and light and electron microscopic evaluation of tumor-bearing rats demonstrated that osteosarcomas in rats inoculated at Day 4 of age were more osteoproliferative osteosarcomas than those in rats inoculated on Day 1. Rats inoculated at 4 days of age lived longer, had more slowly growing osteosarcomas, and developed a consistent tumor-associated cachexia compared to tumor-bearing rats inoculated at Day 1. Both groups of rats had a 93% metastasis rate involving either sublumbar lymph nodes, lungs, or both. Tumor-bearing rats inoculated at 4 days of age had consistent elevations in both urinary hydroxyproline excretion (HOP/CR) and serum alkaline phosphatase levels, and in serum calcium levels at some time points. The high tumor incidence after a short latent period and the morphologic and biochemical similarities between the MSV-induced murine osteosarcoma and the osteosarcoma in human beings makes this discrete tumor and a valuable animal model for the evaluation of new therapeutic regimens.     

Morphologic studies in the skeletal dysplasias.

Considerable progress has been made in the delineation of the genetic skeletal dysplasias, a heterogeneous group of disorders, that consist of over 80 distinct conditions. Morphologic studies have added a further dimension to the delineation of these conditions, their diagnosis, and the investigation of their pathogenetic mechanisms. In certain diseases, the morphologic alterations are characteristic and pathognomonic. In others only nonspecific alterations are observed, whereas in still other disorders growth-plate structure is essentially normal. Histologic, histochemical, and electronmicroscopic studies of growth-plate cartilage have provided new insights into the complexity of morphogenetic events in normal growth through the demonstration of morphologic defects in the genetic disorders of skeletal growth. As yet, very little is known of the biochemical abnormalities underlying the morphologic abnormalities. However, the great variety of morphologic findings points to a number of different pathogenetic defects in the synthesis, release, and assembly of connective tissue macromolecules and in the cells involved in growth-plate metabolism.     

Morphologic alterations in somatotrophs of the rat adenohypophysis following administration of hypothalamic extracts

Hypothalamic extracts injected intravenously into rats produced morphologic alterations in somatotrophs of the pars distalis as observed with light and electron microscopy. Histological changes were correlated with pituitary growth hormone content as determined by bioassay by the tibia test in the same tissue samples. Statistical analysis of data derived from fine structure (number of secretory granules/somatotroph profile) was useful as an index of granule storage and release. Increased numbers of secretory granules, hypertrophy of the Golgi complex, and increased granule extrusion which were observed within five minutes after injection of hypothalamic extract supported the concept that growth hormone-relasing factor in the hypothalamic extract was effective not only in releasing growth hormone but also in stimulating its biosynthesis. Significant increases in both growth hormone content and granule counts agreed with this concept. Extremes of granulation and variable organelle morphology were apparent 15 minutes after injection with hypothalamic extract, although overall granule counts and bioassable growth hormone were within normal limits. By 30 minutes somatotrophs depleted of granules were common, suggesting granule release of major proportion which was consistent with significant decreases in number of granules and growth hormone content. Granules remaining in somatotrophs were aligned peripherally. Vesicular Golgi complexes were prominent. Increased numbers of presumed lysosomes may be related to membrane and/or secretory product accumulation which may result from granule synthesis and release. Somatotrophs from control rats appeared normal.     

Response of tanycytes of rat median eminence to intraventricular administration of colchicine and vinblastine.

The effects of colchicine and vinblastine on tanycytes of the rat median eminence have been studied using the electron microscope. Colchicine and vinblastine were administered by intraventricular cannulation into the third ventricle and demonstrated distinct morphological effects on tanycyte microtubules. Highest drug doses administered were 50.0 mug in 5.0 mul of saline initially, followed by an additional 50.0 mug of these agents infused in a volume of 13.0 mul saline over an hour. Colchicine treatment resulted in the formation of large crystalloids within tanycytes, coincident with the disappearance of microtubules, all along the ventricular surface. Nonetheless the tanycytes appeared able to maintain a continuous, tight lining, as in controls, although some crystalloids were observed beneath the ventricular surface, either within tanycyte processes or within neuronal processes. Vinblastine treatment also resulted in the formation of identical crystalloids but at highest doses thoroughly destroyed the tanycyte lining of the median eminence and exposed cellular elements below the surface to the drug. Portal capillaries approaching the ventricular surface were generally free of any signs of drug response to either colchicine or vinblastine.     

Morphologic and functional evidence for oxygen deficiency in the isolated perfused rat kidney

Morphologic and functional studies were undertaken in the isolated rat kidney, perfused with an albumin-Krebs-Henseleit solution, to which 5% human erythrocytes and/or various amino acids had been added. Perfused only with the albumin-Krebs-Henseleit solution, the kidneys displayed a characteristic pattern of cell necrosis after 2 hours of perfusion, which was confined to the interbundle region of the outer medulla and was not evident in either the cortex or the inner medulla. In the outer stripe only those proximal straight tubules (P3 segments) farthest from the vascular bundles were damaged. In the inner stripe only those thick ascending loops of Henle at the periphery of the vascular bundles escaped damage; all thick ascending loops of Henle lying farthest from the bundles were severely damaged. The number of damaged tubules increased toward the border to the inner medulla. Necroses in both segments, P3 and thick ascending loops of Henle, could be prevented by perfusion with the erythrocyte-albumin-Krebs-Henseleit solution but not by the addition of glutathione, in the absence of erythrocytes. Perfusion with the erythrocyte medium also significantly improved glomerular filtration rate and sodium and glucose reabsorption. It is concluded that, in the isolated, erythrocyte-free perfused kidney, the oxygen content of the "arterial" vasa recta in the vascular bundles is only sufficient to supply the tubules in the immediate surroundings. Countercurrent exchange in the vascular bundles between arterial and "venous" vasa recta progressively lowers the arterial oxygen content as the inner stripe of the outer medulla is approached and with it the number of tubules receiving an adequate oxygen supply.     

Absorption of folic acid by everted segments of rat jejunum

1. Everted rings of rat intestine were used to study the initial uptake rate of folic acid at various concentrations and incubation temperatures in vitro.2. Folic acid was accumulated linearly for periods of at least 30 min.3. The initial uptake rate was found to reach a constant value as the concentration of folic acid in the incubation medium was increased above 5 x 10(-6)M.4. Reducing the temperature of incubation from 37 to 27 degrees C gave small Q(10) values at either end of the concentration range.5. Transfer of folic acid into the serosal compartment of everted sacs was shown to undergo a rate reduction in the same concentration range.6. A mechanism for folic acid transport is suggested in which folic acid is converted to the neutral species at the mucosal surface in an acid microclimate.     

Lysosome lipid storage disorder in NCTR-BALB/c mice. II. Morphologic and cytochemical studies.

Electron-microscopic and cytochemical studies were carried out on tissues of NCTR-BALB/c mice. These mice are affected with a neurovisceral genetic disorder involving excessive tissue accumulation of lipid. Distinctive polymorphic intracellular inclusions, bounded by a membrane and containing lamellated bodies, were found in many cells of liver, spleen, lung, kidney, intestine, lymph nodes, and brain. The inclusions transformed reticuloendothelial cells into massive foam cells. Acid phosphatase cytochemical studies performed on sections of liver demonstrated that the inclusions were lysosomes. Fixation of liver in the presence of digitonin produced "spicules" in the inclusions characteristic of digitonin-cholesterol complexes. Clefts of cholesterol crystals were seen in the inclusions in liver, spleen, and lung. We conclude that the NCTR-BALB/c mice are affected by a lysosome lipid storage disease and that cholesterol is a major storage product.     

Handling of uric acid by the rat kidney

Summary Under free flow conditions there is a net transport of uric acid in the rat proximal tubule. This net transport is the result of two unidirectional fluxes which in the range of normal plasma concentrations of uric acid follow a first order kinetic, i.e. the unidirectional fluxes are in linear proportion to uric acid concentration in tubular fluid or in plasma, respectively. The transport coefficient of the influx (in secretion direction) exceeds that of the outflux (in reabsorption direction) by a factor of 2.5.This study was partially supported by a grant of the Deutsche Forschungsgemeinschaft.