The effect of cardiac contraction on collateral resistance in the canine heart.
We determined whether the coronary collateral vessels develop an increased resistance to blood flow during systole as does the cognate vascular bed. Collateral resistance was estimated by measuring retrograde flow rate from a distal branch of the left anterior descending coronary artery while the main left coronary artery was perfused at a constant pressure. Retrograde flow rate was measured before and during vagal arrest. We found that in 10 dogs the prolonged diastole experienced when the heart was stopped caused no significant change in the retrograde flow rate, which indicated that systole has little effect on the collateral resistance. However, when left ventricular end-diastolic pressure was altered by changing afterload or contractility, a direct relationship between end-diastolic pressure and collateral resistance was noted. (+info
Effect of tumor necrosis factor alpha on vascular resistance, nitric oxide production, and glucose and oxygen consumption in perfused tissue-isolated human melanoma xenografts.
The effect of tumor necrosis factor alpha (TNF-alpha) on vascular resistance, nitric oxide production, and consumption of oxygen and glucose was examined in a perfused tissue-isolated tumor model in nude mice. One experimental group was perfused with heparinized Krebs-Henseleit buffer, a second one was perfused with TNF-alpha (500 microgram/kg) 5 h before perfusion. The vascular resistance increased significantly 5 h after TNF-alpha injection. The increase in vascular resistance did not seem to be mediated by a decrease in tumor nitric oxide production, as determined by perfusate nitrate/nitrite concentrations, but may be due to aggregation of leukocytes, platelets, and erythrocytes and/or endothelial consumption among the three experimental groups. The oxygen consumption was linearly dependent on the amount of available oxygen in the perfusate, whereas the glucose consumption was constant and independent of the glucose delivery rate. The present experiments provide new insights into physiological and metabolic mechanisms of action of TNF- alpha for optimization of future treatment schedules involving TNF-alpha. (+info
Drug-protein binding and blood-brain barrier permeability.
The permeability surface area (PS) product, an index of permeability of the blood-brain barrier (BBB), was measured by using the in situ perfusion method. In the cerebral circulation, the fraction of drug that permeates into the brain through the BBB is not only the unbound fraction but also the fraction dissociated from the protein in the perfusate. The sum of these two fractions, the apparent exchangeable fraction, was estimated by fitting the parameters of the BBB permeability under the condition of varying BSA concentrations in the perfusate. The unbound fraction of drugs in a buffer containing 0.5 mM BSA was measured by using the ultrafiltration method in vitro, and the apparent exchangeable fraction was measured in vivo by using the intracarotid artery injection method. The apparent exchange fraction was 100% for S-8510, 96.5% for diazepam, 90.9% for caffeine, 38.3% for S-312-d, 33.1% for propranolol, and 6.68% for (+)-S-145 Na, and each of these was higher than the corresponding unbound fraction in vitro in all drugs. The apparent exchangeable fractions, for example, were 8 times higher for diazepam and 38 times for S-312-d than the unbound fractions in vitro. The apparent exchangeable fraction of drugs was also estimated from the parameters obtained with the perfusion method. Because drugs can be infused for an arbitrary length of time in the perfusion method, substances with low permeability can be measured. The apparent exchangeable fractions obtained with this method were almost the same as those obtained with the intracarotid artery injection method. (+info
Effects of inhibitors and substitutes for chloride in lumen on p-aminohippurate transport by isolated perfused rabbit renal proximal tubules.
The transport step for p-aminohippurate (PAH) from cell to lumen across the luminal membrane of rabbit proximal tubules has not been adequately defined. To examine this process more closely, we determined the effects of possible transport inhibitors and substitutes for chloride on PAH secretion in isolated perfused S2 segments of rabbit proximal tubules. The addition of 4-acetamido-4'-isothiocyano-2,2' disulfonic stilbene (10(-4) M) to the perfusate irreversibly inhibited PAH secretion, whereas the addition of probenecid (10(-4) M) to the perfusate reversibly inhibited PAH secretion. PAH secretion was unaffected by thiocyanate replacement of chloride in the luminal perfusate, reversibly inhibited by 15 to 20% by methyl sulfate replacement, and irreversibly inhibited by isethionate replacement. Because the luminal membrane is at least as permeable to thiocyanate as to chloride, less permeable to methyl sulfate, and much less permeable to isethionate, these data suggest that the PAH transport step from cells to lumen does not require chloride in the lumen but does require a highly permeant anion. During inhibition of PAH transport from cells to lumen, PAH uptake across the basolateral membrane was also reduced, suggesting some type of feedback inhibition. The data are compatible with PAH transport across the luminal membrane by an anion exchanger, a potential-driven uniporter, both carriers, or a carrier that can function in both modes. (+info
The mechanism of the increasing action of TA-993, a new 1,5- benzothiazepine derivative, on limb blood flow in anesthetized dogs: selective suppression of sympathetic nerve activity.
TA-993, (-)-cis-3-acetoxy-5-(2-(dimethylamino)ethyl)-2, 3-di-hydro-8-methyl-2-(4-methylphenyl)-1,5-benzothiazepin-4(5H)one maleate, a new 1,5-benzothiazepine derivative with l-cis configuration, has a unique and selective increasing action on limb blood flow with little influence on arterial pressure besides an antiplatelet action. We studied the mechanism of increasing action of TA-993 on limb blood flow in anesthetized dogs. In a canine blood-perfused hindlimb preparation with a donor dog, TA-993 (100 microg/kg i.v.) did not increase femoral blood flow when administered to the donor dog, but did when administered to a recipient dog. TA-993 did not show the increasing action on femoral blood flow in the presence of hexamethonium or phentolamine, whereas it did in the presence of propranolol or atropine. TA-993 also showed a weak increasing effect on heart rate, which was inhibited by any one of these blockers. TA-993 (300 microg/kg i.v.) did not alter the phenylephrine (1-100 ng/kg i.a.)- or the talipexole (3-100 ng/kg i.a.)-induced increase in perfusion pressure in an autoperfused hindlimb. These results suggest that the increasing action of TA-993 on limb blood flow is mediated by the sympathetic nervous system but that the adrenergic receptors are not likely to be the central point of action of this new agent. There is a possibility that the mechanism of the increasing action on heart rate is different from that of its increasing action on limb blood flow. (+info
Activation of the kallikrein-kinin system in hemodialysis: role of membrane electronegativity, blood dilution, and pH.
BACKGROUND: The kallikrein-kinin system activation by contact with a negatively charged surface has been promulgated to be responsible for hypersensitivity reactions. However, to explain the low frequency and heterogeneity of hypersensitivity reactions, we hypothesized that not only the electronegativity of the membrane, but also other physicochemical parameters could influence the activation of the contact phase system of plasma assessed by the measurement of kallikrein activity and bradykinin concentration. METHODS: Plasma kallikrein activity using chromogenic substrate (S2302) and plasma bradykinin concentration (enzyme immuno assay) were measured during the perfusion of human plasma (2.5 ml/min) through minidialyzers mounted with six different membranes [polyacrylonitrile (PAN) from Asahi (PANDX) and from Hospal (AN69), polymethylmethacrylate (PMMA) from Toray, cellulose triacetate (CT) from Baxter, cuprophane (CUP) from Akzo and polysulfone (PS) from Fresenius]. RESULTS: A direct relationship was shown between the electronegativity of the membrane assessed by its zeta potential and the activation of plasma during the first five minutes of plasma circulation. With the AN69 membrane, the detection of a kallikrein activity in diluted plasma but not in undiluted samples confirmed the importance of a protease-antiprotease imbalance leading to bradykinin release during the first five minutes of dialysis. With PAN membranes, the use of citrated versus heparinized plasma and the use of various rinsing solutions clearly show a dramatic effect of pH on the kallikrein activity and the bradykinin concentration measured in plasma. Finally, increasing the zeta potential of the membrane leads to a significant increase of plasma kallikrein activity and bradykinin concentration. CONCLUSIONS: Our in vitro experimental approach evidences the importance of the control of these physicochemical factors to decrease the activation of the contact system. (+info
Three-independent-compartment chamber to study in vitro commissural synapses.
We describe a novel chamber in which the two intact neonatal rat hippocampi and the commissural fibers are placed in three independent compartments separated by latex membranes and perfused selectively with different solutions. A set of control tests showed that the compartments are well isolated: 1) methylene blue or eosin applied to one compartment did not diffuse to other compartments when verified via the microscope, and spectrophotometry revealed that <1/10.000th of the dye diffuses to other compartments; 2) tetrodotoxin (1 microM) applied to the commissural compartment blocked the synaptic responses evoked contralaterally without affecting those evoked on the ipsilateral side. This chamber enables a wide range of experiments that cannot be performed in conventional chambers, e.g., to study the maturation and plasticity of the commissural connections, bilateral synchronization of the rhythmic activities in the limbic system, commissural propagation of the epileptiform activities, etc. (+info
Influence of renal failure on intestinal clearance of ciprofloxacin in rats.
Following intravenous doses, ciprofloxacin pharmacokinetics in control and nephrectomized rats were studied. There were no differences between control and nephrectomized rats for area under the concentration-time curve in plasma or biliary clearance. The intestinal clearance of ciprofloxacin was increased in nephrectomized rats. Intestinal elimination seems to compensate partially for the decrease in urinary excretion of ciprofloxacin in nephrectomized rats. (+info