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Biomedical subjects

K Brendel

Publications and source records attributed to K Brendel.

At least 73 records · Page 4Linked to original sources
PubMed1990

Toxicity of halothane in guinea pig liver slices.

Guinea pigs have proven to be a reliable model of halothane associated hepatotoxicity. An in vitro system with Hartley male guinea pig liver tissue was designed to assess the toxicity of halothane and other volatile anesthetics in the target organ. Precision-cut guinea pig liver slices (250-300 microns) were incubated in sealed roller vials containing Krebs-Henseleit buffer (plus vitamins, amino acids, glutamine, gentamycin) at 37 degrees C, under 95%, 21% and 5% O2/CO2 atmospheres. Halothane (10-15 microliters) was injected through a Teflon septa cap on a filter paper wick and vaporized. Viability of the slices was monitored by measuring intracellular K+ content which was maintained under 95% O2 up to 24 h. A dose- and time-related decrease in intracellular slice K+ by 1.9, 2.1, 2.7 mM halothane in the media was observed. At 2.7 mM halothane a direct physio-chemical effect may be occurring since incubating liver slices from allylisopropyl-acetamide-treated animals did not protect against the drop in intracellular K+. Concentration/time responses of halothane, d-halothane, enflurane, isoflurane and sevoflurane were compared. Sevoflurane had no effect on the liver slice K+ content up to 24 h while the other anesthetics caused the following rank-order decrease in intracellular K+ content: halothane greater than isoflurane and enflurane greater than d-halothane. Precision-cut cultured guinea pig liver slices offer a system where the target tissue for intoxication by anesthetics can be examined for its susceptibility and mechanism of intoxication.

Anesthetics↗
PubMed1990

Cocaine hepatotoxicity in cultured liver slices: a species comparison.

Studies were carried out in order to find a sensitive in vitro model with which to investigate cocaine-mediated hepatotoxicity. Precision-cut liver slices were prepared from: human, domestic pig, New Zealand white rabbit, Sprague-Dawley (S/D) rat, and two mouse strains (DBA/2Ha and ICR). The rationale for the choice of these species was that information on in vivo effects of cocaine was available in the literature. Slices were cultured for up to 6 h in the presence of 0-5 mM cocaine. Indices of toxicity consisted of K+ retention and Ca2+ uptake. Minimal effects and no clear dose-response relationships were observed. In addition to the studies with non-pretreated animals, liver slices were prepared from DBA/2Ha and ICR mice, both induced by housing on pine shavings, and phenobarbital pretreated Sprague-Dawley rats. The induced ICR mouse and rat were approximately 3 times more sensitive to cocaine-mediated hepatotoxicity. The following order of sensitivity to cocaine-mediated hepatotoxicity was established: induced rat = induced ICR mouse much greater than induced DBA/2Ha mouse = rabbit = uninduced ICR mouse = uninduced DBA/2Ha mouse = uninduced rat greater than pig = human.

Adolescent↗
PubMed1990

Morphological studies of cellular responses to experimental arterial grafts.

Cross-carotid microvascular bypass grafts 2-3 mm in diameter were implanted using microsurgical techniques for end-to-end anastomosis in four dogs. One autograft control and one of three denatured human umbilical artery xenografts (HUAG) were patent at 5 weeks. One of the other two denatured HUAGs had thrombosed at 1 week, and the other was occluded at 5 weeks. Host and graft vessel specimens were evaluated histologically as well as with transmission electron microscopy after sacrifice. Results indicate that failure of reconstitution of a true endothelial layer, presence of a subintimal myofibroblast population, increased collagen deposition of the muscularis, and occlusion of the adventitial and mural microcirculation were observed in both the early and late nonpatent vessels but not in the patent specimens. Evidence for myointimal cell proliferation was present in both patent and occluded grafts. A cohesive intimal layer was observed in both patent cases. Microvascular occlusion, due to an excess of endothelial cells, of new vasa vasorum in one case seems related to increased fibrosis, which could have resulted in graft stenosis. The surgical procedures and subsequent morphological analyses were adequate and sufficient for use in a long-term study of the possible causes of graft failure.

Anastomosis, Surgical↗
PubMed1990

Assessment of S-(1,2-dichlorovinyl)-L-cysteine induced toxic events in rabbit renal cortical slices. Biochemical and histological evaluation of uptake, covalent binding, and toxicity.

A renal cortical slice system was utilized to investigate the events leading to site-specific nephrotoxicity induced by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). DCVC uptake into renal cortical slices was shown to be rapid (5-15 min) as well as time- and concentration-dependent. Of the total amount taken up at 1 h, 40% was subsequently covalently bound. These observations were confirmed by autoradiography, illustrating uptake and binding in the proximal tubule cells. Following these events, toxicity was evidenced by alterations in ATP content and O2 consumption between 4 and 8 h as well as leakage of the brush border enzymes (gamma glutamyl transpeptidase and alkaline phosphatase) as early as 4 h. Light microscopy provided a sequence of histopathological changes from an initial S3 lesion between 4 and 8 h to a lesion encompassing all proximal tubule segments (by 12 h). Electron microscopy demonstrated not only the specificity of DCVC toxicity (at 6 h) but also illustrated mitochondrial damage and loss of brush borders. A comparison of continuous versus short-term exposure to DCVC indicated that an irreversible sequence of events was initiated as early as 30 min. By utilizing an in vitro model which allows correlation of biochemical and histological changes, a sequence of events leading to DCVC induced toxicity was established.

Animals↗
PubMed1990

Determination and metabolism of dithiol chelating agents. VII. Biliary excretion of dithiols and their interactions with cadmium and metallothionein.

N-(2,3-Dimercaptopropyl) phthalamidic acid (DMPA), meso-dimercaptosuccinic acid (DMSA), and 2,3-dimercapto-1-propanesulfonic acid (DMPS) are dithiol chelating agents with antidotal activity for lead, mercury, arsenic, and other heavy metals. The biliary excretion of these compounds was studied in male Sprague-Dawley rats. After iv administration of DMPA, 72% of the injected dose was recovered in the bile. Half of the recovered DMPA was in the unaltered form (parent compound) and the other half was in the altered form (parent compound recovered after chemical reduction by DTT). An altered, presumably disulfide, form of DMPS was found in the bile. Neither unaltered nor altered DMSA was detected in the bile. DMPA (0.10 mmol/kg), given to rats 3 days after exposure to Cd, elicited within 30 min a 20-fold increase in biliary Cd excretion. The increase of biliary Cd by DMPA was dose-related and not due to an increase of bile flow rate. DMSA and DMPS did not significantly affect the biliary excretion of Cd. Incubation of DMPA or DMSA with Cd-saturated metallothionein (MT) resulted in the removal of Cd from MT. DMPA was more active than DMSA in this respect. The evidence strongly supports the mechanism that the increase of biliary cadmium following DMPA administration is the result of DMPA entering cells and mobilizing and removing the cadmium from MT. The removal of cadmium from metallothionein by dithiol chelating agents provides another dimension to their mechanisms of action and may provide an important new tool for the study of cadmium as well as metallothionein.

Animals↗
PubMed1990

Neuropeptide processing in regional brain slices: effect of conformation and sequence.

The central enzymatic stability of des-enkephalin-gamma-endorphin and its synthetic analogs [cycloN alpha 6, C delta 11]beta-endorphin-[6-17] and [Pro7, Lys(Ac)9]-beta-endorphin[6-17] was studied in vitro using a newly developed, regionally dissected rat brain slice, time course incubation procedure. Tissue slice viability was estimated as the ability of the brain slice to take up or release gamma-[3H]aminobutyric acid after high K+ stimulation. Results demonstrated stability of uptake/release up to 5 hr of incubation, suggesting tissue viability over this period. The estimated half-life of peptides based on the results obtained in our incubation protocol suggest that the peptides studied are metabolized at different rates in the individual brain regions tested. A good correlation exists between the high enzyme activity of neutral endopeptidase (EC 3.4.24.11) and the rapid degradation of des-enkephalin-gamma-endorphin and [cycloN alpha 6, C delata 11]beta-endorphin-[6-17] in caudate putamen. Proline substitution combined with lysine acetylation appears to improve resistance to enzymatic metabolism in caudate putamen and hypothalamus. However, cyclization of des-enkephalin-gamma-endorphin forming an amide bond between the alpha-NH2 of the N-terminal threonine and the gamma-COOH of glutamic acid did not improve peptide stability in any brain region tested. The present study has shown that the brain slice technique is a valid and unique approach to study neuropeptide metabolism in small, discrete regions of rat brain where peptides, peptidases and receptors are colocalized and that specific structural modifications can improve peptide stability.

Amino Acid Sequence↗
PubMed1989

N-acetyl S-(1,2-dichlorovinyl)-L-cysteine produces a similar toxicity to S-(1,2-dichlorovinyl)-L-cysteine in rabbit renal slices: differential transport and metabolism.

Renal cortical slices were used to determine the toxicity of N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (N-acetyl-DCVC) as well as to investigate the transport and metabolism of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and the N-acetyl derivative. N-Acetyl-DCVC produced dose- and time-dependent decreases in intracellular K+ content and lactate dehydrogenase activity. Histopathology demonstrated an initial S3 lesion followed by a lesion inclusive of all proximal tubules. N-Acetyl-DCVC was shown to be transported via the organic anion system by its ability to inhibit PAH transport by the cells and the ability of probenecid to decrease uptake (80%) and toxicity of N-acetyl-DCVC. DCVC, in contrast, was not transported by the organic anion system, but may be transported by one or more amino acid systems. N-Acetyl-DCVC must be deacetylated before undergoing metabolism by beta-lyase. This process must occur since covalent binding of a 35S-labeled reactive product from N-acetyl [35S]DCVC is observed within 1 hr. Both the uptake inhibitor, probenecid, and aminooxyacetic acid (AOAA), a beta-lyase inhibitor, decreased the covalent binding from N-acetyl [35S]DCVC (80 and 50%, respectively), but only AOAA inhibited the covalent binding of DCVC. AOAA also partially inhibited the toxicity of DCVC and N-acetyl-DCVC as determined by intracellular K+ content, lactate dehydrogenase activity, and histopathology. Despite the fact that a separate transport system and an additional enzymatic step (deacetylation) are required, N-acetyl-DCVC produces a lesion with similar intratubular specificity to that seen with DCVC. Therefore, the S3 specificity seen in vivo could be produced by either compound.

Acetylation↗
PubMed1989

In vitro and in vivo nephrotoxicity of the L and D isomers of S-(1,2-dichlorovinyl)-cysteine.

The toxicity of the optical isomers S-(1,2-dichlorovinyl)-L-cysteine (L-DCVC) and S-(1,2-dichlorovinyl)-D-cysteine (D-DCVC) was investigated in vivo and in vitro. In vitro studies, utilizing a rabbit renal cortical slice system, demonstrated toxicity due to both forms with the L-form being more toxic. Dose- and time-dependent decreases in intracellular K+ and LDH were observed. Both compounds produced an initial S3 lesion, L-DCVC at 10(-5) M (12 h), D-DCVC at 10(-4) M (8 h), followed by a lesion encompassing all proximal tubules. In vivo studies demonstrated elevated blood urea nitrogen values at 24 and 48 h with 25 mg/kg of either isomer. Histopathology indicated both D and L-DCVC produced a straight proximal tubular lesion by 48 h, the lesion produced by L-DCVC being more severe. The D and L isomers of DCVC were both shown to be toxic, the toxicity assessed in vitro corresponded well with the toxicity in vivo.

Animals↗
PubMed1988

Changes in the fatty acid profile of lung, liver and serum of rats intratracheally given silica.

The esterified (E) and nonesterified (NE) fatty acid level and profile in the lung, serum, and liver of rats are significantly altered after intratracheal administration of silica. The changes include a silica-specific increase of the total long chain (C16-C20:4) fatty acid content in the lung, and a decrease in the serum and liver of both groups of rats intratracheally given silica and/or saline. In the silicotic lung, arachidonate and palmitate accumulated at the highest rate. A heat-labile, high-molecular weight component from lung homogenates increases lipogenesis in isolated hepatocytes in vitro. These findings, taken together with evidence indicating increased lipogenesis in the liver of rats treated with silica under identical conditions, suggest a lung-liver communication mechanism which coordinates lipid uptake by the lung and lipid synthesis and release by the liver. The stimulatory factor identified in lung homogenates might play an important regulatory role-for hepatic lipogenesis in rats developing silicotic lungs.

Animals↗
PubMed1988

Perifused precision-cut liver slice system for the study of hormone-regulated hepatic glucose metabolism.

A nonrecirculatory perfusion system for precision-cut rat liver slices has been developed and utilized for investigating hormone-regulated hepatic glucose metabolism. In this system, slices are cultured in a highly controlled environment and exhibit excellent retention of viability as judged by their maintenance of intracellular potassium and glycogen contents. Using this system, the complex physiological phenomenon of hormone-regulated glycogenolysis was investigated at both extra- and intracellular sites. Specifically, the sensitive responses of intracellular cyclic AMP (cAMP) production, activation of cyclic AMP-dependent protein kinase, and production of glucose upon glucagon stimulation have been measured. The maximal responses observed for these parameters were either equal to or greater than those previously reported for either isolated hepatocytes or perfused livers, demonstrating the sensitivity of this technique. Upon dose-response examination of glucagon challenge, it was observed that high doses of glucagon (greater than 16 nM) stimulate glucose production by activating the cAMP-second messenger cascade. In contrast, low doses (less than 4 nM) stimulate this process without production of intracellular cAMP or activation of cAMP-dependent protein kinase, suggesting the operation of cAMP-independent messenger. Since this system permits measurements of parameters common to many cellular processes, this methodology is suitable for addressing both pharmacological and toxicological questions.

Animals↗
PubMed1988

Rat liver slices and diazepam metabolism: in vitro interactions with volatile anaesthetic drugs and albumin.

The influence of the volatile anaesthetic agents enflurane, isoflurane, halothane and the halothane metabolite trifluoroacetic acid was studied on the hepatic elimination of diazepam, by incubating precision-cut slices of rat liver in a closed system. The impact of anaesthetic-induced action on enzyme activity and diazepam binding to human serum albumin (HSA) was assessed in protein free and protein containing buffers, respectively. Human serum albumin reduced the elimination of diazepam by 12 and 50% at concentrations of 1 and 10 mg ml-1, respectively. In the absence of albumin, halothane 1 mmol litre-1 reduced the elimination of diazepam by 13%, whereas enflurane at 1.5 mmol litre-1 caused a reduction of 8%. No effect was seen from isoflurane 1 mmol litre-1 and trifluoroacetic acid 4 mmol litre-1. In the presence of the highest concentration of albumin, however, an increased elimination of diazepam of 24% resulted from exposure to enflurane and trifluoroacetic acid, while no statistically significant changes were seen for isoflurane and halothane. The present work supports the view that volatile anaesthetic agents may cause pharmacokinetic drug interactions by interference with both enzyme activity and drug protein binding.

Anesthetics↗
PubMed1987

Cisplatin nephrotoxicity: in vitro studies with precision-cut rabbit renal cortical slices.

Severe nephrotoxic side effects limit the use of cisplatin, a potent anticancer drug. In this study, precision-cut renal cortical slices from rabbits were evaluated as a cisplatin nephrotoxicity model. Cortical slices accumulated approximately 180 ppm (195 ppm Pt = 10(-3) M) of platinum(II) after 18 hr of incubation in medium containing 10(-3) M cisplatin. Dose- and time-dependent toxic responses for clinically relevant concentrations of cisplatin (10(-3)-10(-5) M) were apparent using leakage of intracellular K+, ATP, and lactate dehydrogenase (LDH) to determine cell damage. Histopathologic changes were also produced. Intracellular ATP levels dropped significantly after 6 hr of incubation in 10(-3) M cisplatin, and after 12 hr with 10(-4) M cisplatin. Similarly, intracellular K+ levels decreased significantly by 6 hr of incubation with 10(-3) M cisplatin but remained at control levels for 18 hr in the presence of 10(-4) M cisplatin. Decrements in intracellular LDH levels were not seen until after 12 hr of incubation in 10(-3) M cisplatin. The noncytotoxic isomer transplatin at 10(-3) M was not accumulated by slices; however, intracellular ATP levels were depressed. Of the viability parameters evaluated, intracellular K+ and ATP were found to be optimal indicators. Other active platinum analogs, carboplatin and iproplatin, also caused dose- and time-dependent leakage of intracellular K+ and ATP from renal cortical slices. The ranking of nephrotoxicity of the platinate compounds within this system at concentrations adjusted to approximate equivalent therapeutic activity was similar to that observed in vivo (cisplatin = iproplatin greater than carboplatin greater than transplatin). These results suggest that precision-cut renal cortical slices comprise a viable in vitro model for platinum-induced nephrotoxicity studies.

Adenosine Triphosphate↗
PubMed1987

Differential patterns of injury to the proximal tubule of renal cortical slices following in vitro exposure to mercuric chloride, potassium dichromate, or hypoxic conditions.

The innate susceptibility of renal cell types to these agents was investigated using precision-cut rabbit renal cortical slices made perpendicular to the cortical-papillary axis. Slices were incubated in DME/F12 medium containing 10 microM, 100 microM, or 1 mM concentrations of either metal for 12 hr or in Krebs-Hepes buffer gassed with nitrogen (100%) for 0.75 to 5 hr of hypoxic exposure. To simulate postischemic reperfusion, some slices were transferred to vessels gassed with oxygen after an initial hypoxic period. Mercuric chloride (100 microM) exposure resulted in damage to the straight regions of proximal tubules by 12 hr leaving convoluted regions unaffected. Hypoxia (2.25 hr) and potassium dichromate (100 microM for 12 hr) both caused injury to the convoluted proximal tubules without affecting straight proximal tubular regions. Mercury concentrations of 10 microM and 1 mM had no effect or injured all cell types within the slice, respectively. Similar results were observed for hypoxic periods less than 1.5 hr or greater than 3 hr of exposure. Potassium dichromate had no measurable affect at 10 microM, but at 1 mM focal lesions were observed after 4 hr of exposure, and by 12 hr all cell types within the slice were affected. Intracellular potassium content normalized to DNA correlated well, but always preceded the pathological lesions observed. These results demonstrate that injury to specific regions of the proximal tubule by these agents relates to an innate susceptibility of the intoxicated cell type independent of physiologic feedback or blood delivery patterns proposed as mechanisms of selective injury from in vivo studies.

Animals↗