Biomedical subjects

K Spokes

Publications and source records attributed to K Spokes.

At least 37 records · Page 2Linked to original sources

PubMed1993

Chronic amphotericin nephropathy: morphometric, electron microscopic, and functional studies.

The two major hypotheses for the pathogenesis of amphotericin nephrotoxicity are direct interaction with epithelial cell membranes and vasoconstriction. Studies indicating the special vulnerability of the medullary ray and medulla to hypoxia led to a reexamination of amphotericin nephrotoxicity. Twenty-four rats were divided into four groups: amphotericin injection (5 mg/kg daily for 3 wk), amphotericin plus salt depletion, vehicle, and salt depletion and vehicle. The amphotericin group had polyuria (P < 0.01) but normal serum creatinine. In contrast, amphotericin plus salt depletion rats exhibited renal failure (creatinine of 1.49 +/- 0.05 versus amphotericin alone 0.98 +/- 0.01; P < 0.01). Semiquantitative histologic analysis of cortical and medullary injury correlated with functional impairment. Cortical changes in the amphotericin group were largely restricted to the medullary ray, where focal rupture and calcification of thick ascending limbs were noted. The S2/S3 tubules in the medullary rays showed focally diminished cell complexity with histiocytic/lymphocytic infiltration. However, calcification was also seen in the area of the macula densa. Morphometry revealed that the thick ascending limbs in the medulla were hypertrophied (1,420 +/- 63 versus 1,195 +/- 48 microns 2 for vehicle; P < 0.05). In contrast, in the amphotericin and salt depletion group, the changes in the medullary ray extended to the labyrinth and the thick ascending limbs in the inner stripe showed atrophic changes (772 +/- 23 microns 2; P < 0.01 versus vehicle). Thus, changes as a result of amphotericin toxicity take place both in areas known to be most vulnerable to hypoxia (medullary ray and medulla), and in areas rich in oxygen (adjacent to glomerulus). Salt depletion potentiates the cortical changes and converts medullary hypertrophy to atrophy. These findings support a dual pathogenesis for amphotericin nephropathy (direct toxicity and vasoconstriction).

Amphotericin B↗

PubMed1992

Effect of glycine and hypertrophy on renal outer medullary hypoxic injury in ischemia reflow and contrast nephropathy.

Glycine preserves tubular cell integrity under hypoxic and toxic conditions in vitro. It also ameliorates cisplatin nephrotoxicity in vivo. We studied the effect of glycine on tubular necrosis from ischemia reflow and on inner stripe injury in an animal model of radiocontrast nephropathy. In all experiments, glycine (75 mg/100 g/h) increased tubular damage in the inner stripe. In the model of radiocontrast nephropathy, the percentage of medullary thick ascending limb (mTAL) necrosis at 24 hours increased from 22% +/- 6% to 41% +/- 9% or 55% +/- 7% with glycine infusion of 75 or 135 minutes, respectively (mean +/- SE, P less than 0.05, analysis of variance [ANOVA]). Renal function was not significantly affected. In rat kidneys subjected to ischemia reflow, mTAL injury following glycine increased from 1% +/- 0% to 12% +/- 6% (P less than 0.05) and from 8% +/- 5% to 49% +/- 8% (P less than 0.01) 24 hours after 30 minutes and 45 minutes ischemia, respectively. Tubular injury in the inner stripe was maximal in the deep interbundle zone, typical of hypoxic, rather than reperfusion, injury. Prior uninephrectomy increased inner stripe damage, but protected the proximal tubules. Both uninephrectomy and glycine infusion were found to contribute to mTAL necrosis. The infusion of glycine for 1 hour in intact rats increased renal blood flow by 44% and tripled urine volume (P less than 0.01). A parallel increase in glomerular filtration rate GFR; by 22% over 90 minutes) fell short of statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Mechanism of glycine protection in hypoxic injury: analogies with glycine receptor.

Addition of glycine to the recirculating perfusate of isolated perfused rat kidneys protects against hypoxic injury to the medullary thick ascending limb and slows functional deterioration in the course of perfusion. This effect is dependent on dose; the earliest significant protection is seen at 0.25 mM, and the protective effects increase as glycine concentration is increased to 2 mM, the highest level tested. Two specific agonists of the strychnine-insensitive (NMDA) glycine receptor in neural membranes, 1-aminocyclopropane carboxylic acid (ACC) and d-serine, also exerted a cytoprotective effect at a concentration of 2 mM. On the other hand, 1-serine and taurine, ineffective agonists of the NMDA-glycine receptor but effective agonists of the strychnine-sensitive glycine receptor, had no protective effect in this system. Two antagonists to glycine at its binding site on the N-methyl-D-Aspartate (NMDA) receptor, 7-chlorokynurenic acid (2 mM) and indole-2-carboxylic acid (12.5 mM), did not reverse the cytoprotective action of 0.25 mM glycine. The data are consistent with a ligand-acceptor type of interaction to account for cytoprotection. The configuration of the glycine acceptor may resemble, but is not identical with, that of certain glycine receptors in the nervous system.

Animals↗

PubMed1992

In-vivo and in-vitro studies on the effect of amphotericin B on endothelin release.

Since amphotericin B nephrotoxicity is mediated, in part by hypoxic tubular injury, the role of endothelin in the renal vasoconstriction, characteristic of amphotericin toxicity has been studied. Intact and salt depleted rats were infused with amphotericin B (20 micrograms/kg per min) or 5% dextrose over 20 min. Plasma endothelin levels determined at the conclusion of the infusion period, did not differ between the experimental groups, despite a marked reduction in renal blood flow noted in rats infused with amphotericin B. Amphotericin B (10(-5)-10(-7) M) did not stimulate endothelin release from cultured bovine aortic endothelial cells. However, in a model of chronic amphotericin nephrotoxicity produced by repeated daily intraperitoneal injections of amphotericin B (5 mg/kg) to salt depleted rats, renal failure was associated with elevated plasma endothelin levels (29.3 +/- 4.4 fmol/mL, vs 10.8 +/- 1.2 fmol/mL in salt depleted controls, P less than 0.01). We conclude that while plasma endothelin may be increased in chronic amphotericin B nephropathy, this peptide does not mediate the acute renal vasoconstriction associated with the infusion of this drug.

Amphotericin B↗

PubMed1992

Radiocontrast agents induce endothelin release in vivo and in vitro.

The intravascular administration of the ionic radiocontrast agent sodium iothalamate (2.9 g of iodine/kg body wt) to rats induced an increase in plasma concentration of immunoreactive endothelin from 21.3 +/- 1.2 to 36 +/- 3 fmol/mL, preceded by a transient rise in the plasma level of atrial natriuretic peptide and associated with a fall in RBF. Equi-iodine amounts of the nonionic agents ioxaglate and iohexol elicited similar or more marked changes in plasma endothelin, but hypertonic solutions of NaCl, mannitol, or glucose did not. Comparable levels of endothelin produced by infusions of endothelin-1 induced a reduction of up to 29% in RBF. Iothalamate and iohexol stimulated endothelin release from cultured bovine endothelial cells, suggesting a direct effect of ionic and nonionic agents on vascular endothelium. The data invite speculation that under some circumstances endothelin release might play a role in the circulatory changes caused by these compounds and in the pathogenesis of radiocontrast nephropathy.

Animals↗

PubMed1991

Toxicity of adenine nucleotides in the isolated perfused kidney: selective destruction of the S2 segment of the proximal tubule.

In an attempt to ameliorate the morphological abnormalities and decreased renal function produced by hypoxia in the isolated perfused rat kidney, adenosine triphosphate (ATP) was added to the perfusate medium. No improvement was noted in the histological changes or renal function. Paradoxically, however, in oxygenated control kidneys, ATP (2.5-10 mM), caused a severe injury remarkably limited to the S2 segments of proximal tubule. This injury was more destructive than that observed with complete ischemia for the same period of time or with inhibitors of glycolysis, intermediary metabolism, or respiratory chain function. Tubular damage produced by ATP was paradoxically prevented by hypoxia and mitochondrial inhibition. The mechanism of this selective toxic injury to the proximal tubule remains unclear and may depend upon intact transport metabolism of the cell.

Adenosine Diphosphate↗

PubMed1991

Protective action of glycine in cisplatin nephrotoxicity.

Because glycine is cytoprotective for kidney cells in vitro, we investigated its possible action in vivo to protect rats against cisplatin nephrotoxicity, a well-established experimental model of renal tubular injury. Glycine was infused at a dose of 1 mmol per 100 g body weight per hour for 75 minutes, starting 15 minutes before cisplatin, 5 mg per kg, was injected intravenously. Plasma concentration of glycine rose to 3.5 mmol per liter at the time cisplatin was injected. These rats were compared with cisplatin-treated animals treated with L-alanine or with isotonic saline. After five days plasma creatinine of saline-treated rats given cisplatin had risen threefold to 2.6 +/- 1.5 mg per 100 ml (mean +/- SD), as creatinine clearance fell to 25% of baseline (0.14 +/- 0.05 ml/min/100 g). Morphological evaluation disclosed extensive damage involving all S3 segments in the outer medulla as well as the medullary rays of the cortex. In contrast, in rats treated with glycine, plasma creatinine rose only to 1.2 +/- 0.2 mg/100 ml and creatinine clearance was maintained at 75% of baseline (0.35 +/- 0.05 ml/min/100 g). Glycine also attenuated the weight loss, polyuria, increased fractional excretion of sodium and potassium, decreased urinary osmolality, and renal glycosuria observed in control, saline-treated rats after cisplatin, while substantially decreasing the percentage of S3 tubules with evident morphological injury. Renal platinum content was unaffected by glycine. The administration of L-alanine or the delayed infusion of glycine, starting one hour after cisplatin was given, did not prevent cisplatin toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Early renal medullary hypoxic injury from radiocontrast and indomethacin.

We evaluated the acute changes in cortical and outer medullary oxygen tension and the alterations in renal function and morphology within the first 90 minutes after the administration of indomethacin and iothalamate to anesthetized Sprague-Dawley rats. Both agents were found to produce marked and protracted outer medullary hypoxia averaging 12 +/- 4 and 9 +/- 2 mm Hg, respectively (mean +/- SE). Given together to salt depleted uninephrectomized rats they produced an early hypoxic injury localized selectively in the outer medulla. This lesion progressed from 3 +/- 1% of medullary thick ascending limbs (mTALs) at 15 minutes to 22 +/- 7% at 24 hours. Condensed "dark" cells were observed at 15 minutes, probably representing a type of early injury. Residual red cell mass, quantified in the outer medullary vasculature of perfusion-fixed kidneys and presumably reflecting stasis, was substantially increased in iothalamate treated rats. Red cell mass in the interbundle zone correlated with mTAL necrosis. Taken together, these results show an early period of medullary hypoxia, accompanied by a selective injury to mTALs in the central interbundle zone with apparent stasis. These findings contrast sharply with the ischemia-reflow pattern of renal damage and emphasize the important role of medullary hypoxia in the genesis of acute renal failure in this model.

Animals↗

PubMed1991

Effect of glycine on medullary thick ascending limb injury in perfused kidneys.

The addition of 2 mM glycine to the recirculating perfusate of isolated perfused rat kidneys almost completely prevented the severe morphological injury to tubular cells lining the medullary thick ascending limb (mTAL) that normally develops in this preparation. Glycine was similarly effective in reducing mTAL injury associated with hypoxic perfusion, indomethacin and amphotericin. Fractional reabsorption of sodium was increased with glycine, without any change in perfusate flow to the whole kidney and without consistent improvement in GFR. L-alanine demonstrated a similar though less pronounced cytoprotective action, but glutamine, cysteine, glutamate, cysteine plus glutamate, 1-serine and 4-aminoisobutyric acid all had little or no effect in preventing severe mTAL injury. The protective effect of glycine was unimpaired by the arginine analogue NG-monomethyl-l-arginine (L-NMMA), suggesting that the endothelial-derived relaxing factor, NO, was not involved. The action of glycine was not reduced by the addition of a substrate (benzoate) or a product (hippurate) of the glycine N-acyltransferase reaction. Glycine did not depress the respiration of dispersed mTALs prepared from rat kidneys. The cytoprotective effect of glycine in the mTAL of perfused kidneys, shared with l-alanine, appears to be relatively specific for these amino acids and probably unrelated to a diminution in cell work.

Amino Acids↗

PubMed1990

Influence of endogenous prostaglandins on mTAL injury.

We altered renal prostaglandin production by isolated rat kidneys in several ways to see if this would influence the susceptibility of cells lining the medullary thick ascending limb to injury. Rats were fed a diet containing either safflower oil (high in linoleic acid) or fish oil (low in arachidonate precursors) as a source of fat. After 90 min of perfusion, the kidneys of rats fed safflower oil showed only 32.7 +/- 6.7% of medullary thick ascending limb cells near the inner medulla with severe damage, whereas the same zone in perfused kidneys of rats fed fish oil showed 96.6 +/- 1.3% severely damaged cells (P less than 0.01). The protection afforded by safflower oil was accompanied by a doubling of urinary excretion of PGE2 and 6-keto-PGF1 alpha, and was eliminated by indomethacin, which suppressed prostaglandin synthesis. Perfusion with bradykinin also greatly increased prostaglandin excretion and reduced severe medullary thick ascending limb damage in the deepest zone of the outer medulla from 51.3 +/- 6.6% in controls to 28.5 +/- 5.9% (P less than 0.02). The protection provided by bradykinin was also completely reversed by indomethacin. The results suggest that endogenous prostaglandins serve a protective function against hypoxic injury for cells of the medullary thick ascending limb.

Animals↗

PubMed1990

Relation of adenosine to medullary injury in the perfused rat kidney.

In isolated perfused rat kidneys the medullary thick ascending limb (mTAL) is uniquely vulnerable to cellular injury produced by its hypoxic milieu and exacerbated by active transport. Endogenous inhibitors of transport might therefore be expected to reduce cell injury. We studied the possible role of adenosine in altering mTAL damage in isolated rat kidneys perfused for 60 min. When adenosine deaminase was added to the recirculating perfusate in 8 experiments, severe damage to mTAL cells adjacent to the inner medulla was significantly exacerbated to involve 89.4 +/- 3% of them as compared to 74.9 +/- 4.7% in 9 controls (p less than 0.025). Similar results were obtained when 6-nitrobenzylthioinosine, which inhibits adenosine efflux from hypoxic cells, was added to the perfusion (n = 5, p less than 0.025). The addition of the adenosine analogue R(-)-phenylisopropyladenosine [R(-)-PIA] conferred protection, so that now only 12.5 +/- 2.5% of deep mTAL cells exhibited severe morphological damage (n = 7, p less than 0.005). The protective effect of R(-)-PIA was minimized by 8-phenyltheophylline, which blocks adenosine receptors. The S(+)-isomer of PIA was significantly less potent than R(-)-PIA in protecting against hypoxic injury. These results suggest that endogenous adenosine may play a role in modifying the injurious effects of anoxia on medullary cells, by inhibiting active transport.

Adenosine↗

PubMed1989

The effect of organotin compounds on chloride secretion by the in vitro perfused rectal gland of Squalus acanthias.

The effects of various organotins on membrane function and electrolyte transport were studied in the marine elasmobranch, Squalus acanthias. The isolated perfused rectal gland was used as a model of electrolyte transport. This gland can be stimulated to secrete chloride by atrial natriuretic peptide, veratrine, and vasoactive intestinal polypeptide although the mechanism of action of each secretagogue is different. By analysis of the inhibitory effect of an organotin in the presence of each secretagogue, the mechanism of inhibition can be inferred. Tributyltin (TBT) produced a reversible inhibition of epithelial transport at 10(-8) to 10(-7) M which resulted from inhibition of stimulus-secretion coupling in VIP-containing neurons within the gland. The transporting epithelial cells were unaffected at these concentrations. Trimethytin (TMT) produced inhibition at 10(-7) M which was not reversible and which affected primarily the transporting epithelial cells. Triethyltin and triphenyltin were without effect. The inhibitory effect of TBT and TMT was not affected by simultaneous administration of dithiothreitol. TBT also produced inhibition of oxygen consumption, Na+,K-ATPase, and proton ATPase in dispersed rectal gland cells. These results indicate that organotins are toxic to cell membrane functions which are intimately involved in the movement of electrolytes. This is the first evidence of toxicity to membrane transport functions in a marine species which is at risk from environmental exposure.

Animals↗

PubMed1989

Polyethylene glycol effect on the oxygenated and hypoxic isolated perfused rat kidney.

Polyethylene glycol protects against O2 deprivation after clamping of the renal artery or norepinephrine infusion and in hypoxic primary cell culture. Isolated perfused kidneys under hypoxic conditions develop morphological alterations in all segments of the proximal tubule and medullary thick ascending limb. In an attempt to ameliorate the effect of hypoxia, rat kidneys were perfused for 90 min with regularly oxygenated (95% O2 + 5% CO2) or hypoxic perfusate (95% N2 + CO2) supplemented with 8-12% polyethylene glycol (MW approximately 8000). In oxygenated and hypoxic kidneys, polyethylene glycol produced similar changes in S1-S2 segments consisting of reduction of cell thickness and organelle compaction with internalization of brush border into the tubulo-vesicular system. In the S3 segment, the cellular volume loss was more limited; the brush border was transformed to membranous whorls and the cytoplasm contained large, irregular, clear zones. Mitochondrial swelling was pronounced in the hypoxic proximal tubules. Polyethylene glycol quantitatively increased and emphasized the damage in the medullary thick ascending limb. Inclusion of 10(-2) M ouabain preserved the medullary thick ascending limb from hypoxic injury and polyethylene glycol had no effect on this undamaged epithelium. Thus, polyethylene glycol affects renal tubules on the basis of their known water permeability and does not protect against but rather worsens hypoxic injury in the medullary thick ascending limb.

Animals↗

PubMed1989

The vulnerability of the thin descending limbs of Henle's loop in the isolated perfused rat kidney.

In the isolated rat kidney perfused without erythrocytes, the medullary thick ascending limb shows extensive injury. Damage to the thin limbs of Henle's loop has been mentioned only briefly. Thin limbs were examined in the isolated perfused kidney under a variety of conditions that alter oxygenation and active transport in the medulla and are known to affect injury to the medullary thick ascending limb. The thin descending limbs of short loops were preserved in all experimental groups, but those of the long loop showed necrosis that was restricted to the proximal portion, where the epithelium is more complex. In oxygenated kidneys, necrosis involved 41% +/- 5% (mean +/- SE) of the medullary thick ascending limbs and 10% +/- 3% of the proximal portion of long loops of thin descending limbs. Under hypoxic conditions, necrosis involved 90% +/- 3% of the medullary thick ascending limbs and 70% +/- 5% of the proximal portion of long loops of thin descending limbs (P less than 0.0001 compared with oxygenated kidneys). Ouabain and absence of filtration completely prevented necrosis of both nephron segments. Thus, the proximal portions of long loops of thin descending limbs, in resemblance to medullary thick ascending limbs, are especially susceptible to transport-dependent hypoxic injury.

Animals↗

PubMed1989

Renal medullary Na-K-ATPase and hypoxic injury in perfused rat kidneys.

We wished to see if chronic alterations in Na-K-ATPase activity in the medullary thick ascending limb would modify the susceptibility of its cells to the hypoxic injury produced by perfusion of the isolated kidney. Rats were fed a diet high (64%) or low (8%) in protein for three weeks. Renal medullary Na-K-ATPase was 75 +/- 12 U/mg protein/hr (mean +/- SE) in the high protein group and 44 +/- 3 in rats given low protein. After 90 minutes of perfusion, the kidneys of rats fed a high protein diet showed almost all mTAL cells near the inner medulla with severe damage (93 +/- 4.8%), whereas the same zone in perfused kidneys of rats on a low protein diet showed only 47 +/- 7.7% injury. In a similar fashion, damage to mTAL cells seen in perfused kidneys was greatly augmented by compensatory renal hypertrophy produced by removal of the contralateral kidney two weeks earlier, and by a diet high in potassium given for two weeks, procedures which also increased the activity of medullary Na-K-ATPase. The results suggest that the level of transport work of medullary cells mediated by Na-K-ATPase is a determinant of the vulnerability of mTAL cells to hypoxic injury.

Animals↗

PubMed1987

Role of alpha-adrenergic hormones in potassium homeostasis in the rat.

To determine whether alpha-adrenergic stimulation impairs extrarenal potassium disposal in the rat, we studied the effect of an alpha-agonist and antagonist on the rise in plasma potassium concentration produced by a potassium infusion of 3 mEq KCl/kg over a 90-minute period to nephrectomized rats. Compared with KCl alone, the alpha-agonist phenylephrine caused more than a 25% increment in the peak plasma potassium, and reduced the volume of distribution of the potassium load. Addition of the alpha-blocker, phentolamine, to phenylephrine completely abolished the increment in potassium caused by KCl infusion. There were no differences in plasma bicarbonate, arterial pH, or plasma glucose levels among the groups. When an identical protocol was performed in nephrectomized rats also prepared by adrenalectomy, induction of diabetes, and chemical sympathectomy, the rise in plasma potassium level after KCl infusion was again augmented by phenylephrine. Addition of phentolamine also markedly blunted the increment in potassium in this group. These results show that alpha-adrenergics impair extrarenal potassium disposal in the rat. The effect does not depend on endogenous insulin or other potassium-regulatory factors. alpha-Adrenergics appear to play an important role in extrarenal potassium homeostasis.

Adrenalectomy↗

PubMed1986

Mitochondrial activity: a possible determinant of anoxic injury in renal medulla.

In brain, heart and kidney, cell work in the absence of oxygen has been thought to precipitate anoxic damage by increasing the rate of depletion of cellular energy stores. In the medullary thick ascending limb of isolated perfused rat kidneys, however, reduction of ATP synthesis by a variety of mitochondrial or metabolic inhibitors caused ATP depletion comparable to that produced by oxygen deprivation but did not reproduce the lesions of anoxia. In these cells, unrestrained mitochondrial activity may be an important source of anoxic injury.

Adenosine Triphosphate↗

PubMed1986

Differential responsiveness of proximal tubule segments to metabolic inhibitors in the isolated perfused rat kidney.

Rat kidneys were perfused for 90 minutes with cyanide, rotenone, antimycin, 2-deoxyglucose, or combinations of rotenone or antimycin with 2-deoxyglucose in oxygenated Krebs-albumin medium. Following perfusion, proximal tubule injury was evaluated by light microscopy. The types of lesions seen were similar to those previously reported after hypoxic perfusion and included brush border clubbing/mitochondrial swelling in S1 and S2 and cytoplasmic edema or cell fragmentation in S3. This finding supports the contention that these lesions represent characteristic responses of these segment types and that the S3 response differs from that in S1 and S2. S1 appeared most vulnerable to low dose cyanide or inhibition of mitochondrial electron transport (rotenone, antimycin). Inhibition of glycolysis (2-deoxyglucose) only produced injury in S2 tubules. With high dose cyanide or a combination of 2-deoxyglucose with either rotenone or antimycin, there was diffuse proximal tubule damage. Thus S3 appeared more resistant than the convoluted tubular segments to both inhibition of glycolysis and to inhibition of mitochondrial electron transport. This finding stands in contrast to the selective vulnerability of the S3 segment in ischemic renal injury.

Animals↗