Biomedical subjects

K Spokes

Publications and source records attributed to K Spokes.

51 records · Page 3Linked to original sources

PubMed1986

Hypoxic injury in the proximal tubule of the isolated perfused rat kidney.

The effect of hypoxia on the morphology of the proximal tubule was examined in isolated rat kidneys perfused with Krebs-albumin medium, gassed with 95% N2/5% CO2 for 45, 90 and 190 min. The major findings were heterogeneity of types of cell injury and definable topographical zones of protection from damage. The characteristic injury in S1 and S2 was that of mitochondrial swelling and brush border alterations that progressed to complete disorganization of this zone. S3 manifested two distinct lesions, one characterized by cell swelling and the other by tubular epithelial fragmentation. Protection from these injuries was seen in tubules located in periarterial zones, apparently due to gradients of oxygenation. The same types of injury but without zones of protection were seen after perfusion with cyanide (10 mM) in oxygenated medium. A "reflow" period of oxygenated perfusion did not alter the fundamental character of these lesions but affected tubules showed progression of damage while there was preservation of tubules in periarterial areas. Thus the responses of the proximal tubule to hypoxic injury depends both on segment type (S1, S2 versus S3) and on tubular location in relation to O2 availability. Additional factors appear to determine the type of response in S3 tubules.

Animals↗

PubMed1986

Transport-dependent cell injury in the S3 segment of the proximal tubule.

Two distinct types of injury, cytoplasmic edema and cell fragmentation occur in the S3 segment of the proximal tubule in isolated hypoxic perfused rat kidneys (Krebs-albumin medium gassed without O2). The proportion of S3 tubules with fragmentation strongly correlated with the GFR and urine output during the perfusion, and approached 100% when the GFR was increased by high perfusion pressure. Conversely, the fragmentation lesion was absent and the edema lesion extensive when tubular transport was inhibited by perfusion with hyperoncotic medium to prevent glomerular filtration or by addition of ouabain (10(-2) M) to the perfusate. Polyene antibiotics increase membrane permeability and thus the work of active electrolyte transport. Perfusion with amphotericin (3 X 10(-5) M) or nystatin (200 U/mliter) in oxygenated medium also produced fragmentation in S3. The lesion was prevented in the non-filtering kidney. Ouabain completely eliminated the cell fragmentation due to nystatin and significantly reduced that due to amphotericin. These results suggest that the injury of cell fragmentation is enhanced by transport activity and diminished when transport is inhibited. The edema lesion appears fundamentally different and more akin to lesions described in ischemia where tubular flow is absent, active transport is diminished, and the morphologic changes appear related to loss of cell volume regulation. The type of hypoxic damage exhibited by proximal tubular S3 segments may therefore be conditioned by active ion transport of tubular cells.

Amphotericin B↗

PubMed1986

Substrates induce hypoxic injury to medullary thick limbs of isolated rat kidneys.

Under certain conditions, excess of substrates may be detrimental to the kidney. In isolated rat kidneys perfused with cell-free medium, oxidative metabolism to support reabsorptive transport in the presence of a limited oxygen supply results in hypoxic injury to medullary thick ascending limbs (mTAL). Since inhibitors of mitochondrial respiration markedly reduced this injury, we evaluated the effects of altering the availability of substrate for oxidative metabolism in the mTAL. Inhibition of glucose utilization with 2-deoxyglucose (50 mM) and simultaneous inhibition of long-chain fatty acid metabolism with 2-tetradecylglycidic acid (10(-4) M) in the absence of exogenous substrates consistently reduced hypoxic cell injury to mTAL. Similarly, the direct inhibition of substrate oxidation by the citric acid cycle with monofluoroacetate (5 mM) also reduced the extent of damage to this nephron segment. Bypassing these metabolic blockades with L-lactate, pyruvate, or alpha-ketoglutarate stimulated renal oxidative metabolism and increased hypoxic damage to mTAL. Enhanced renal metabolism and function (higher renal oxygen consumption, tubular reabsorption of sodium, and glomerular filtration rate) were paradoxically associated with greater damage to mTAL. Thus, when oxygen supply is limited, substrate-supported aerobic metabolic activity for tubular transport may induce hypoxic injury in the renal medulla.

Animals↗

PubMed1986

Lactate increases potassium secretion by perfused rat kidney.

The effect of exogenous metabolic substrates on K+ secretion was evaluated in the isolated perfused rat kidney in the presence of 2-deoxyglucose and 2-tetradecylglycidic acid to inhibit utilization of glucose and fatty acids from endogenous sources. L-Lactate (15 mM) added to the perfusion medium enhanced renal oxygen consumption (4.0 +/- 1.1 mumol X min-1 X g-1 vs. 2.0 +/- 1.0 without lactate) while decreasing fractional excretion of sodium (19.3 +/- 2.4% vs. 47.3 +/- 1.8). L-Lactate markedly increased the fractional excretion of K+ to 181 +/- 29% compared with 68 +/- 12% without lactate (P less than 0.001). The poorly metabolized isomer D-lactate did not alter these parameters. The addition of alpha-ketoglutarate only slightly increased K+ excretion. In the absence of metabolic inhibitors and in the presence of glucose (5 mM), L-lactate also increased K+ excretion significantly more than did D-lactate (108 +/- 19% vs. 69 +/- 11, P less than 0.02). At the end of 90 min of perfusion with L-lactate medium, K+ concentration in the perfusate dropped from 4.7 +/- 0.05 to 3.2 +/- 0.2 meq/liter (vs. 3.8 +/- 0.1 meq/liter with D-lactate, P less than 0.005) without differences in glomerular filtration rate or sodium excretion. L-Lactate appears to increase K+ secretion by preferential metabolic stimulation of the distal tubule, a process that may help in vivo to prevent hyperkalemia in lactic acidosis.

Amiloride↗

PubMed1986

Isolated rectal gland cells: oxygen consumption and hormonal stimulation.

Cells isolated from rectal glands of Squalus acanthias, using collagenase and hyaluronidase digestion, retained normal morphological characteristics as judged by light microscopy of 1-micron plastic sections. Their oxygen consumption per unit weight was comparable to that of intact rectal gland studied either in situ, or by isolated perfusion, as well as that of rectal gland slices. Cellular respiration was stimulated by dibutyryl cyclic AMP and theophylline or by vasoactive intestinal peptide which stimulate secretion of chloride by the intact gland. Stimulated oxygen consumption was inhibited by ouabain and bumetanide and was proportional to the concentration of sodium or chloride in the incubation solution. The oxygen consumption of these cells parallels the secretory and metabolic behavior of the intact rectal gland, suggesting that it reflects energy demands for ion transport. The relative ease with which a homogeneous preparation of viable and active cells can be obtained and the apparent preservation of many of their key functional characteristics make this preparation a useful tool for the study of hormone-stimulated ion transport.

Adenosine↗

PubMed1986

Inhibition of prostaglandin synthesis in rat kidney perfused with and without erythrocytes: implication for analgesic nephropathy.

A marked defect in renal concentration ability associated with hypoxic lesions in the medullary thick ascending limb (mTAL) characterizes the isolated rat kidney perfused with cell-free solutions. Addition of erythrocytes to the perfusion medium, a maneuver known to eliminate signs of hypoxic cellular injury to mTALs, greatly improved renal concentrating ability. When indomethacin was given to kidneys perfused with erythrocyte-enriched medium, concentrating ability was further improved by the drug to an average U/Posm of 2.45 +/- 0.81, and medullary cellular structure remained normal in appearance. Since renal hypoperfusion predisposes to acute renal failure from non-steroidal antiinflammatory drugs (NSAIDs) and medullary ischemia might play a role in chronic analgesic nephropathy, a synergism between NSAIDs and medullary hypoxia was evaluated in the isolated perfused rat kidney. Indomethacin and naproxen added to the perfusion medium (at 10(-4) and 5 X 10(-4) M, respectively) effectively depressed prostaglandin E2 (PGE2) production by the isolated kidney but did not improve its concentrating ability when perfused with cell-free medium. Quantitation of hypoxic injury to mTALs, regularly observed in this model, indicated that both indomethacin and naproxen increased the extent and severity of damage in the deeper, most hypoxic portions of the inner stripe. Addition of PGE2 to cell-free perfusate reduced the extent of hypoxic damage to the mTAL. These results suggest that in medullary hypoxia, prostaglandins protect mTAL cells by either vasodilatation or reduction in active transtubular transport. NASAIDs, by suppressing prostaglandin production, could predispose the renal medulla to hypoxic injury.

Amino Acids↗

PubMed1985

Disparate mechanisms for hypoxic cell injury in different nephron segments. Studies in the isolated perfused rat kidney.

Hypoxic injury was evaluated morphologically in the proximal tubule and in the medullary thick ascending limb of isolated rat kidneys perfused for 90 min without O2 or with various metabolic inhibitors. Inhibition of mitochondrial respiration (with rotenone, antimycin, oligomycin) or of intermediary metabolism (with monofluoroacetate, malonate, 2-deoxyglucose) caused reduction in renal oxygen consumption, renal function, and ATP content comparable with those elicited by oxygen deprivation. Metabolic inhibition produced hypoxiclike injury in the first portions of the proximal tubule, S1 and S2 ("clubbing" of microvilli, mitochondrial swelling), and the extent of damage was correlated with the degree of ATP depletion. In the third portion of the proximal tubule, S3, hypoxiclike damage (cytoplasmic edema or fragmentation) occurred most consistently when both aerobic and anaerobic metabolism were inhibited simultaneously. In the medullary thick ascending limb, none of the metabolic or mitochondrial inhibitors used could reproduce the injury of oxygen deprivation. Thus, the proximal tubule and the thick ascending limb have markedly different responses to cellular energy depletion, suggesting disparate mechanisms for hypoxic injury along the nephron.

Adenosine Triphosphate↗

PubMed1984

Polyene toxicity in renal medulla: injury mediated by transport activity.

Polyene antibiotics such as amphotericin and nystatin increase membrane permeability and thus increase the amount of oxygen consumed in active electrolyte transport. In isolated perfused rat kidneys, the polyenes produced extensive injury to the medullary thick ascending limb, a segment of the nephron with limited oxygen supply. This damage was prevented if reabsorptive transport was inhibited by ouabain. Cell death under these circumstances thus appears to be mediated by increased oxygen demand for transport activity.

Amphotericin B↗

PubMed1984

Transport-dependent anoxic cell injury in the isolated perfused rat kidney.

The hypothesis that decrease in energy demand may prevent anoxic cell damage has been examined in the medullary thick ascending limb of isolated perfused rat kidneys exposed to oxygen deprivation. The effects of decreasing active reabsorptive transport in the medullary thick ascending limb were observed on the extensive damage regularly induced by hypoxic perfusion (gassed with no oxygen) or potassium cyanide. Anoxic injury was consistently attenuated or abolished if reabsorptive transport was decreased with ouabain or furosemide or by halting the glomerular filtration rate with the use of a hyperoncotic medium (nonfiltering kidney). Comparison of the injury generated by warm ischemia for identical time periods showed that complete ischemia does not reproduce the severe lesions seen during hypoxic perfusion. These results suggest that transport activity is a determining factor of anoxic cell death in the thick ascending limb of Henle's loop.

Animals↗

PubMed1983

Ouabain binding in rectal gland of Squalus acanthias.

In an attempt to examine the mechanisms of activation of (Na, K)-ATPase when epithelial transport is stimulated, the binding of ouabain to rectal gland tissue was measured before and after stimulation with dibutyryl cAMP and theophylline. Stimulation significantly altered the characteristics of ouabain binding to slices of Squalus acanthias rectal gland and to isolated rectal gland cells, accelerating the rate of binding and increasing the amount of ouabain bound at equilibrium when low concentrations of ouabain (10(-9) to 10(-7) M) were present in the medium. Scatchard plots of ouabain binding were nonlinear, suggesting at least two classes of binding sites, one of higher and one of lower affinity. Stimulation with cAMP and theophylline appeared to increase the affinity of the high-affinity site. Ouabain binding was increased by cAMP and theophylline even in the presence of furosemide (10(-4) M) or bumetanide (10(-5) M), and when Li+ was substituted for Na+, or NO3- for Cl- -maneuvers known to inhibit rectal gland secretion. The changes in ouabain binding induced by cAMP and theophylline do not appear, therefore, to be secondary to secretory activity but may reflect a change in the configuration, environment or location of existing enzyme so as to enhance its activity. Stimulation of ouabain binding cannot be demonstrated in whole homogenates of rectal gland, indicating that intact cells are necessary for the cyclic AMP-induced increase in ouabain binding to become manifest.

Animals↗

PubMed1982

Relationship among gluconeogenesis, QO2, and Na+ transport in the perfused rat kidney.

The relationship among sodium transport (TNa), oxygen consumption (QO2), and gluconeogenesis was studied in isolated perfused rat kidneys in which glucose formation was enhanced by providing pyruvate as a substrate and by prior treatment with methylprednisolone. TNa was increased abruptly by increasing perfusion pressure as to increase GFR or by lowering the albumin concentration of a hyperoncotic perfusate as to allow glomerular filtration to occur. Increases in TNa of 40% were accompanied by little or no increase in QO2, whereas gluconeogenesis decreased 55-80%. Conversely, a decrease in perfusion pressure that lowered TNa produced an increase in glucose formation without a change in QO2. When gluconeogenesis was blocked with 0.15 mM 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase, QO2 increased together with TNa as perfusion pressure was raised. The results suggest that the energy needed for ion transport by the kidney may under some circumstances be borrowed from nontransport functions and, therefore, that basal oxygen consumption may vary with the rate of reabsorptive transport.

Animals↗

PubMed1982

Stimulation of renin release by hyperoncotic perfusion of the isolated rat kidney.

Renin release was measured in the isolated rat kidney perfused with a recirculating artificial medium containing bovine serum albumin at 6.7 g per 100 ml of 11 g per 100 ml. At the higher concentration of albumin, glomerular filtration ceased and the rate of renin release over 70 minutes of perfusion was increased 6-fold. The addition of ouabain to the perfusate containing 11 g per 100 ml inhibited the release of renin, suggesting that inhibition of Na-K-ATPase or the related changes in cellular volume or composition prevented renin release. Lowering the osmolality of the perfusate by reducing the concentration of sodium chloride also prevented the increase in renin secretion produced by perfusion with 11 g per 100 ml albumin. Increasing the osmolality of the perfusate with mannitol restored the augmented renin release. These results are consistent with the hypothesis that alterations in the volume of certain cells, perhaps in the juxtaglomerular apparatus itself, can control renin release.

Animals↗

PubMed1981

Sympathetic system in potassium homeostasis.

The extrarenal disposal of potassium was studied in nephrectomized and adrenalectomized rats by measuring the rise in serum potassium produced during an infusion of 3 meq KCl/kg over 90 min. Adrenalectomy alone did not alter the volume of distribution of infused potassium in nephrectomized animals. When nephrectomy and adrenalectomy were combined with either insulin deficiency produced by streptozotocin or chemical sympathectomy induced by injection of 6-hydroxydopamine, potassium tolerance was significantly impaired. Hyperkalemia produced in chemically sympathectomized animals by potassium infusion was minimized by simultaneous infusion of epinephrine, an effect blocked by the beta-antagonist propranolol but not by the alpha-blocker phenoxybenzamine. These results suggest that extra renal uptake of potassium, in addition to being influenced by insulin and circulating catecholamines, is modulated by peripheral sympathetic activity.

Adrenalectomy↗

PubMed1980

Competition between sodium reabsorption and gluconeogenesis in kidneys of steroid-treated rats.

Kidneys of rats treated with methylprednisolone show altered substrate requirements for sodium reabsorption when perfused in vitro. Such kidneys synthesize glucose from lactate at twice the rate of control. Optimum sodium reabsorption is not seen with glucose, which is normally the preferred substrate. Sodium reabsorption is restored toward normal by the combination of glucose and butyrate, by pyruvate, or by 3-mercaptopicolinate. All of these results point to a metabolic adaptation in the kidney; butyrate may improve sodium reabsorption by sparing glucose, pyruvate is a gluconeogenic precursor and an effective fuel of respiration, and 3-mercaptopicolinate is an inhibitor of gluconeogenesis. In kidneys from rats treated with methylprednisolone there is an increased requirement for metabolic energy because of the increased rate of gluconeogenesis. It is suggested that the availability of energy from glucose oxidation is limited in part by the diversion of pyruvate back to glucose. Under these special circumstances, gluconeogenesis competes with sodium reabsorption in the intact kidney.

Animals↗

PubMed1977

Ouabain inhibition of gill Na-K-ATPase: relationship to active chloride transport.

Ouabain circulating in blood inhibits Na-K-ATPase in the gills of seawater eels at a concentration similar to that necessary for inhibition in vitro. By contrast, a much higher concentration is required when ouabain is applied to the exterior of the gill. Inhibition by external ouabain occurs only when the drug gains access to the circulation of the fish, as evidenced by simultaneous inhibition of Na-K-ATPase in the kidney. These results suggest that the Na-K-ATPase of gill chloride cells faces inward, lining intracytoplasmic tubular channels continuous with the extracellular fluid. Inhibition of gill Na-K-ATPase by ouabain in intact salt water eels results in almost complete inhibition of the efflux of both Na+ and Cl-. The efflux is tritiated water was much less reduced, to 60% of normal. Since chloride is actively transported outward across the gill of seawater teleosts, it is suggested that active chloride transport is coupled to Na-K-ATPase. A neutral sodium chloride carrier is postulated that is energized by the movement of sodium from extracellular fluid down its electrochemical gradient into the chloride cell.

Adenosine Triphosphatases↗