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Biomedical subjects

A P Evan

Publications and source records attributed to A P Evan.

17 recordsLinked to original sources
PubMed1979

Development of the intrarenal vascular system of the puppy kidney.

This study investigates the development of the vascular system of the puppy kidney (1-21 days after birth) after preparing casts of the renal vessels. At two days, the intrarenal vascular system distal to the afferent arteriole is strikingly different than that of the adult. The glomeruli of the outer cortex consist of a single dilated vessel while those of the mid and inner cortex posses an increasingly larger number of capillary loops. The efferent arterioles vary greatly in appearance from outer to inner cortex. Those in the nephrogenic zone are characteristically short and narrow and join a larger venous vessel termined a sinusoidal capillary. An efferent system somewhat similar to that of the adult is seen in the mid and inner cortex. One of the most obvious differences noted between the puppy and adult kidney is the relative lack of peritubular capillary networks throughout the cortex of the puppy kidney. The puppy possesses large, irregular vessels termed sinusoidal capillaries. The most rudimentary sinusoids are found in the outer cortex with more mature vessels in the inner cortex. The vascular arrangement of the efferent arteriole and sinusoidal capillary appears as a post-glomerular shunt. Functionally, the shunt would direct blood flow away from the proximal tubule and thus could result in a low extraction ratio and Tm for secreted solutes.

Aging↗
PubMed1979

Maturation of the proximal tubule in the puppy kidney: a comparison to the adult.

Two- to four-day-old beagle puppy kidneys were preapred for transmission and scanning electron microscopy and compared to similarly prepared adult tissues. Proximal tubules of puppy kidneys which contained nephrons in various stages of differentiation were examined and maturational changes were described. Lateral surface contours of proximal tubular cells were initially smooth and relatively unfolded, but progressively acquired complex processes that may be recognized as lateral ridges and lateral-basal processes. Basal projections began as short, stubby processes and gradually took on either a narrow, plate-like or finger-like appearance. Mitochondria lysosomes and apical vacuoles increased in number as the tubules matured. Mitochondria lacked orientation in outer cortical tubules, but exhibited some vertical arrangement within basal processes in inner cortical tubules. Despite features indicating advanced maturation of tubules in the inner cortex, puppy kidneys lacked the lipid droplets characteristic of the adult. Thus, differentiation of this portion of the developing nephron into S1, S2 and S3 segments was not possible at day 4. Morphometric analyses of the lateral and basal membrane surface concentration of proximal convulted tubules from the puppy revealed all cells to have a significantly smaller membrane area than that of the adult. However, the inner cortical cells of the puppy had a greater surface concentration than those of the outer cortex. The reduced transport capacity of the puppy proximal tubule may be realted to the lack of segmentation and/or reduced lateral-basal surface area.

Animals↗
PubMed1979

Polypoid and papillary epithelial hyperplasia: a potential cause of ductal obstruction in adult polycystic disease.

In experimental models of cystic renal disease, functional studies define conditions that suggest increased resistance to outflow from dilated or cystic nephrons. Morphologically, models exhibit foci of cellular hyperplasia and micropolyp formation along outer medullary collecting tubules. Temporally, cellular proliferation precedes cyst formation. These findings in models have led to a hypothesis that polypoid hyperplasia participates in cyst formation in susceptible kidneys by increasing resistance to the outflow of tubular urine. The present study was undertaken to establish the presence, extent, and distribution of cellular hyperplasia in human adult polycystic kidney disease. Kidneys from four unrelated individuals were studied by light and by transmission and scanning electron microscopy. Foci of hocation of hyperplasia along the nephron were similar to those seen in the models. These findings delineate a heretofore unappreciated morphologic similarity between the models and human disease and add further support to the hypothesis that partial rubular obstruction participates in the pathogenesis of renal cystic disease, whether it be heritable or acquired, in animals and in man.

Animals↗
PubMed1979

Nephron obstruction in nordihydroguaiaretic acid-induced renal cystic disease.

Studies were performed to characterize conditions in rat kidneys whose nephrons were made cystic by feeding 2% nordihydroguaiaretic acid (NDGA) to the animals. Using two micropipettes, we monitored intratubular hydrostatic pressures while perfusing single surface nephrons in NDGA-exposed (5 to 7 weeks) and normal rat kidneys. The introduction of 50 nl of Ringers solution labeled with 3H-inulin at a flow rate of 25 nl/min was associated with a significant mean (+/- SEM) increase (167 +/- 61%; P less than 0.02) in pressure in cystic but not in nondilated (-0.5 +/- 27.2%) or normal (31 +/- 23%) nephrons, respectively. The relative amount of 3H-inulin excreted in 40 min from cystic (4.0 +/- 2.0%) was less than that excreted from either nondilated (19 +/- 7%; P less than 0.05) or normal (105 +/- 26%; P less than 0.01) nephrons. Intralumenal pressures in nondilated but not other nephron groups correlated with urinary flow rates (r = 0.51; P less than 0.02). Single nephron filtration rates and tubular-fluid-to-plasma 3H-inulin rations in additional rats were similar among all groups of tubules. Concluding that these data reflected increased resistance to outflow from cystic nephrons, we examined these and additional NDGA-exposed (1 to 24 weeks) kidneys. 3H-thymidine radioautography demonstrated maximum collecting tubular cell hyperplasia (13% labeling) at 2 to 3 weeks of NDGA-exposure. Microscopy and microdissection demonstrated tiny mural polyps along outer medullary segments of collecting tubules. Thirteen tubules were traced to their outlets; polyps impinging on outflow lumens were found in all 13 instances. We conclude that partial nephron obstruction exists in NDGA-exposed kidneys and that obstruction is a likely contributor to cyst formation in this model.

Animals↗
PubMed1979

Renal response to Ringer expansion in developing rats.

Male rats were studied between 20 and 60 days of age. Standard renal clearance techniques were used. The efficiency of the diuretic response, the sodium response, and the potassium response were calculated as defined previously. Results indicate that both diuretic and sodium efficiency is lower between the ages of 20 and 30 days as compared to 40 and 60 days of age, whereas potassium efficiency shows no age dependence. In morphological studies, it has been observed that the proximal tubule cells of 22-day-old rats show changes in lateral intercellular spaces with comparable features to those of mature animals. The spaces widened during volume expansion. The change is quantitatively the same as that found in mature rats. Both blood pressure and hematocrit show continuous increase with age. The response of Ringer infusion in both immature and mature animals may be a mixed response involving changes in physical factors and renal responses to volume expansion per se.

Age Factors↗
PubMed1978

Effects of chronic deafferentation on adrenergic ganglion cells and small intensely fluorescent cells.

To determine the reaction of adrenergic ganglion cells and small intensely fluorescent (SIF) cells to chronic deafferentation, catecholamine fluorescence of the major pelvic ganglion (MPG) of the rat has been studied following section of the hypogastric nerve, pelvic nerve and sympathetic trunk. Only minor changes occurred following section of the hypogastric nerve; the fluorescence surrounding a few adrenergic ganglion cells became brighter. In contrast, pelvic neurectomy resulted in the appearance of numerous varicose fibres and an increase in the fluorescent intensity of fibres enclosing many ganglion cells. Varicose fibres seem to originate from adrenergic ganglion cells and SIF cells. In many instances, nests of SIF cells gave rise to radially oriented fibres. Removal of the sympathetic trunk appeared to have no effect on the MPG. It is suggested that the appearance of varicose fibres from SIF cells following deafferentation may be due to collateral sprouting of these cells or to the increased fluorescence of pre-existing processes.

Adrenergic Fibers↗
PubMed1978

Synergistic nephrotoxicity of amphotericin B and cortisone acetate in mice.

Striking mortality in mice receiving amphotericin B and cortisone acetate concomitantly prompted studies to characterize the toxic interaction of these two drugs further. Adult female CD-1 mice received daily injections of cortisone acetate (0--50 mg/kg subcutaneously) and/or amphotericin B (0--12.5 mg/kg intraperitoneally) in a checkerboard combination dosage pattern for 30 days. Dosages of amphotericin B and cortisone acetate that produced little or no mortality individually produced significant (P less than 0.005) mortality in combination. Light and electron microscopic studies of sections of brain, heart, lung, adrenal gland, liver, and kidney revealed only renal lesions. These appeared within six days, were dose-related in severity, and were not produced by either drug alone. The lesions consisted of focal swelling of proximal, distal, and collecting tubular cells which progressed to necrosis and intraluminal cast formation. These findings may be relevant to the development of nephrotoxicity in patients treated simultaneously with amphotericin B and corticosteroids.

Acetates↗
PubMed1978

Morphology and physiology of the McLeod erythrocyte. I. Scanning electron microscopy and electrolyte and water transport properties.

The McLeod phenotype is a rare condition characterized by deficiencies in the Kell blood group antigens of erythrocytes. The present study has defined some of the morphological and physiological characteristics of these red cells. Scanning electron microscopy reveals that approximately 27% of McLeod cells are morphologically abnormal. These aberrant forms resemble the acanthocytes of abetalipoproteinemia. Incubation experiments indicate that the morphology of McLeod erythrocytes is not due to a plasma factor. Biochemical studies reveal that the lipid composition and microviscosity of these erythrocytes are normal. In addition, isotopic tracer experiments indicate that electrolyte transport is also within the normal range. However, osmotic water permeability is approximately 30% below normal. The absence of a lipid abnormality and other experimental data suggest that the abnormal morphology and reduced H2O permeability of the McLeod erythrocyte may be due to defective membrane protein.

Biological Transport, Active↗
PubMed1978

Changes in structure and function of rat kidney slices produced by low sodium.

The effects of a low Na medium on PAH transport, renal morphology, and acetate stimulation of PAH transport have been studied. Low Na inhibits PAH uptake and induces vacuolar formation in tubular cells. Both processes are reversible by reincubating in a high Na medium. Vacuolization appears temperature dependent being much greater at 37 than at 25 degrees C. Acetate uptake consists of a passive and an active component, neither of which is sodium dependent. Acetate stimulation of PAH uptake does, however, require Na. This latter observation suggests that Na may act by altering cell metabolism.

Acetates↗
PubMed1976

Scanning electron microscopy of cell surfaces following removal of extracellular material.

The application of scanning electron microscopy to the study of cell surfaces is limited in intact tissues, because extracellular material may often obscure the details of nonluminal surfaces. To remove connective tissue elements we have treated human skin and both kidney, and an autonomic ganglion of the rat with hydrochloric acid and collagenase. Regional variations in the basal surface of the nephron are noted following removal of the basement membrane. The basilar interdigitations of the cells of the proximal tubule appeared as parallel ridges encircling the tubule. Ridges on the parietal epithelium of Bowman's capsule were randomly arranged and alternated with smooth surfaces. The dermal surface of the human epidermis has an alveolar or honeycomb appearance due to the elevation of the epidermal ridges and numerous pits for the dermal pegs. At higher magnifications the basal surface of cells of the stratum germinativum possessed numerous and irregular projections. Neurons with their processes are evident in the autonomic ganglion. The soma of the neurons are enclosed by flattened satellite cells. Irregular spaces between opposed satellite cells are interpreted as regions for the passage of processes related to the ganglion cells. Nodes of Ranvier were clearly seen along nerve fibers. Some pitting of the nerve fibers was also noted. The HCl-collagenase method has the advantage of the removal of collagen and basement membrane while preserving the structural integrity of the cell surface.

Animals↗