Babu P. Mathew

Resuscitation with hypertonic saline dextran improves cardiac function in vivo and ex vivo after burn injury in sheep

ABSTRACT In a 24 h, double-blind, prospective trial, we tested the hypothesis that two 4 mL/kg doses of hypertonic saline dextran (HSD; 7.5% NaCl/6% dextran 70) given in addition to isotonic fluid treatment would produce both immediate and sustained benefit for the heart after large burn injury. 12 instrumented sheep were subjected to a 40% total body surface area full-thickness flame burn under halothane anesthesia. 1 h after burn, when the animals had recovered from anesthesia, the first dose of either HSD (n = 6) or normal saline (NaCl .9%; n = 6) was infused over 30 min. The test solution was immediately followed by lactated Ringers solution infused to maintain a urine output of 1–2 mL/kg-h throughout the study. The second dose of test solution was started at 12 h and was infused over 5 h. The initial dose of HSD corrected the burn-induced reduction in cardiac output, cardiac work, an index of myocardial contractility, and restored myocardial blood flow, as measured by the colored micro sphere technique, to preburn values. Plasma concentrations of troponin I, creatine kinase (CK), and CK iso enzyme CKMB were increased 1 h after burn, but were not altered after HSD treatment. After euthanasia at 24 h, myocardial glutathione concentrations were higher in HSD-treated animals, whereas other markers of oxidative injury in heart or in plasma did not show systematic differences. The maximum contraction force measured in isolated right papillary muscles ex vivo was significantly greater in HSD-treated than normal saline-treated animals. In conclusion, the first dose of 4 mL/kg HSD infused 1 h after burn improved cardiac function, whereas the second dose of HSD infused at 12 h was without apparent effect on dynamic variables. An overall effect of the HSD treatments was a lasting increase in papillary muscle contraction force.

Peroxynitrite reduces vasodilatory responses to reduced intravascular pressure, calcitonin gene-related peptide, and cromakalim in isolated middle cerebral arteries.

Vasodilatory responses to progressive reductions in intravascular pressure or to calcitonin gene-related peptide (CGRP) or cromakalim were determined in rodent middle cerebral arteries (MCAs) before and after treatment with peroxynitrite (ONOO−). Middle cerebral artery diameters in isolated, pressurized MCAs were measured as intravascular pressure was reduced from 100 to 20 mm Hg in 20-mm Hg increments before and after inactive ONOO−, pH-adjusted ONOO−, or 10, 20, or 40 μmol/L ONOO− was added to the bath. In other MCAs, responses to CGRP (1 × 10−9 −5 × 10−8) or cromakalim (3 × 10−8 −8 × 10−7) were measured before and after the addition of 25 μmol/L ONOO−. Inactive ONOO− (n = 6, P = 0.40), pH-adjusted ONOO− (n = 6, P = 0.29), and 10 μmol/L ONOO− (n = 6, P = 0.88) did not reduce vasodilatory responses to reduced intravascular pressure. Middle cerebral arteries treated with 20 (n = 6, P < 0.0001) and 40 (n = 6, P > 0.0001) μmol/L ONOO− constricted significantly when intravascular pressure was reduced. Vasodilatory responses to CGRP or cromakalim were reduced by ONOO− (P > 0.02, n = 6 and P > 0.01, n = 7, respectively). ONOO− had no effect on vasoconstriction in response to serotonin or vasodilation in response to KCl. These studies demonstrate that ONOO− reduces multiple cerebral vasodilatory responses.

Role of calcitonin gene-related peptide (CGRP) in ovine burn and smoke inhalation injury

Concomitant smoke inhalation trauma in burn patients is a serious medical problem. Previous investigations in our sheep model revealed that these injuries lead to significant airway hyperemia, enhanced pulmonary fluid extravasation, and severely impaired pulmonary function. However, the pathophysiological mechanisms are still not fully understood. The lung is innervated by sensory nerves containing peptides such as substance P and calcitonin gene-related peptide. Noxious stimuli in the airways can induce a neurogenic inflammatory response, which has previously been implicated in several airway diseases. Calcitonin gene-related peptide is known to be a potent vasodilator. We hypothesized that calcitonin gene-related peptide is also a mediator of the pulmonary reaction to toxic smoke and planned experiments to evaluate its role in this model. We tested the effects of pretreatment with a specific antagonist of the major receptor for calcitonin gene-related peptide (BIBN4096BS; 32 microg/kg, followed by continuous infusion of 6.4 microg.kg(-1).h(-1)) until the animal was killed 48 h after injury in an established ovine model of burn (40% total body surface, third degree) and smoke inhalation (48 breaths, <40 degrees C) injury. In treated animals (n = 7), the injury-related increases in tracheal blood flow and lung lymph flow were significantly attenuated compared with untreated controls (n = 5). Furthermore, the treatment significantly attenuated abnormalities in respiratory gas exchange. The data suggest that calcitonin gene-related peptide contributes to early airway hyperemia, transvascular fluid flux, and respiratory malfunction following ovine burn and smoke inhalation injury. Future studies will be needed to clarify the potential therapeutic benefit for patients with this injury.

Traumatic Brain Injury In Vivo and In Vitro Contributes to Cerebral Vascular Dysfunction through Impaired Gap Junction Communication between Vascular Smooth Muscle Cells

Gap junctions (GJs) contribute to cerebral vasodilation, vasoconstriction, and, perhaps, to vascular compensatory mechanisms, such as autoregulation. To explore the effects of traumatic brain injury (TBI) on vascular GJ communication, we assessed GJ coupling in A7r5 vascular smooth muscle (VSM) cells subjected to rapid stretch injury (RSI) in vitro and VSM in middle cerebral arteries (MCAs) harvested from rats subjected to fluid percussion TBI in vivo. Intercellular communication was evaluated by measuring fluorescence recovery after photobleaching (FRAP). In VSM cells in vitro, FRAP increased significantly (p<0.05 vs. sham RSI) after mild RSI, but decreased significantly (p<0.05 vs. sham RSI) after moderate or severe RSI. FRAP decreased significantly (p<0.05 vs. sham RSI) 30 min and 2 h, but increased significantly (p<0.05 vs. sham RSI) 24 h after RSI. In MCAs harvested from rats 30 min after moderate TBI in vivo, FRAP was reduced significantly (p<0.05), compared to MCAs from rats after sham TBI. In VSM cells in vitro, pretreatment with the peroxynitrite (ONOO(-)) scavenger, 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron[III], prevented RSI-induced reductions in FRAP. In isolated MCAs from rats treated with the ONOO(-) scavenger, penicillamine, GJ coupling was not impaired by fluid percussion TBI. In addition, penicillamine treatment improved vasodilatory responses to reduced intravascular pressure in MCAs harvested from rats subjected to moderate fluid percussion TBI. These results indicate that TBI reduced GJ coupling in VSM cells in vitro and in vivo through mechanisms related to generation of the potent oxidant, ONOO(-).

Effect of quinidine on positive inotropic action of digoxin

To determine whether digoxin-quinidine interaction alters the inotropic effect of the glycoside, the response of peak isometric force and maximal rate of force development (dF/dt) in isolated feline right ventricular papillary muscles to digoxin and quinidine alone, and in various combinations, was examined. The administration of 1.3 or 2.6 x 10(-5) M of quinidine after 2 x 10(-7) M of digoxin resulted in an increase in contractile performance in each animal. Although 1.3 x 10(-5) M of quinidine alone produced a positive inotropic effect, 2.6 x 10(-5) M of quinidine produced no such effect. Because myocardial digoxin content has been reported to decline after administration of quinidine these results suggest that the increase in contractile performance when quinidine was administered after digoxin is due to displacement of digoxin from less to more active myocardial sites. The administration of 2 or 4 x 10(-7) M of digoxin after 2.6 x 10(-5) M of quinidine resulted in a minimal increase in force and rate of force development. A similar inhibition of the inotropic effect of digoxin was found in rabbit papillary muscles pretreated with quinidine. Inhibition was not limited to digoxin because pretreatment of muscles with quinidine also inhibited the inotropic effect of acetylstrophanthidin. Thus, quinidine has diametrically opposite effects on digitalis-induced inotropy dependent on the sequence with which the drugs are administered.

Hydroxyproline and passive stiffness of pressure-induced hypertrophied kitten myocardium.

Passive stiffness and hydroxyproline content of myocardium hypertrophied by pressure-loading were determined in kittens 2, 8-16, and 24-52 wk after pulmonary artery banding, which initially elevated right ventricular systolic pressure by 10-15 mm Hg. Right ventricular mass increased by approximately 75%, three-quarters of which occurred during the first 2 wk after banding. Passive stiffness was assessed from resting length-tension relations of isometrically contracting isolated right ventricular papillary muscles. Stiffness constants, alpha and beta were determined from the relationship sigma = alpha (e beta epsilon - 1) where sigma = stress and epsilon = Lagrangian strain. Elastic stiffness (d sigma/d epsilon) was derived from: d sigma/d epsilon = beta sigma + beta alpha. Right ventricular hydroxyproline increased in proportion to muscle mass so that hydroxyproline concentration remained unchanged after banding. Both alpha, beta, and elastic stiffness-stress relations were similar to values in nonbanded controls. Thus, we did not observe an increase in passive stiffness or hydroxyproline concentration of pressure-stiffness or hydroxyproline concentration of pressure-induced hypertrophied myocardium in contrast to most previous studies.

Myocardial hydroxyproline and mechanical response to prolonged pressure loading followed by unloading in the cat.

To determine the myocardial response to prolonged pressure-loading and unloading, kittens weighing 0.8-1.2 kg underwent pulmonary artery banding, which initially elevated right ventricular (RV) systolic pressure by 10-15 mm Hg. 52 and 76 wk later; RV weight/body weight had increased by approximately 80%. Total RV hydroxyproline had increased significantly, whereas hydroxyproline concentration was unchanged from that of nonbanded animals of comparable age. In isometrically contracting RV papillary muscles, peak active force was significantly less at 76 wk (3.3 +/- 0.8 [SD] g/mm2 than at 52 wk (5.1 +/- 0.8 g/mm2) or in nonbanded animals (4.8 +/- 0.8 g/mm2). Velocity of muscle shortening at comparable loads was unchanged after 52 wk but was significantly less after 76 wk. In nonstimulated, slowly stretched muscles, passive stiffness constants, alpha and beta, derived from delta = alpha(e beta epsilon - 1), where delta is instantaneous stress and epsilon is Lagrangian strain, were unchanged by banding. The band was removed after 52 wk in additional animals that were studied 24 wk later. In those animals with normal RV pressures at death, hypertrophy had regressed and hydroxyproline concentration was comparable to that of nonbanded and banded animals; Active and passive mechanical function remained normal. In this model, changes in hydroxyproline parallel changes in muscle mass, and passive stiffness remains normal during development and regression of hypertrophy. Removal of the pressure load after prolonged hypertrophy prevents or retards the late development of myocardial dysfunction.

Thiopentone inhibits beta-adrenergic responses in myocardial tissue

The purpose of this study was to determine the importance of inhibition of beta-adrenergic function in thiopentone-induced myocardial depression. Using an isolated, electrically stimulated rat left atria model, contractile dose-response curves to thiopentone (200 μM, 400 μM, 600 μM, 800 μM) were shifted to the right in preparations treated with 10− 3 M dibutyryl cyclic adenosine monophosphate (cAMP) compared with atria stimulated with 10− 6 M isoprenaline, demonstrating that inhibition of beta-adrenergic mechanisms by thiopentone is physiologically important. Depression by thiopentone was similar in atria treated with 10− 5 M forskolin compared with preparations stimulated with 10− 6 M isoprenaline, indicating that thiopentone does not block beta-adrenergic receptors. It is concluded that thiopentone depresses myocardial function by several mechanisms, one of which involves inhibition of the adenyl cyclase cascade. The adenyl cyclase enzyme is a likely site where thiopentone inhibits the system; however, other components of the cascade may also be involved.RésuméL’objectif de cette étude consiste à déterminer l’influence de l’inhibition de l’activité β-adrenergique sur la dépression myocardique induite par le thiopentone. A l’aide d’un modèle constitué d’une oreillette gauche de rat stimulée électriquement, la relation dose-effet du thiopentone sur la contractilité (200 μM, 400 μM, 600 μM, 800 μM) se déplace vers la droite dans des préparations traitées avec de l’adénosine monophosphorique cyclique (cAMP) 10− 3 M comparativement à des oreillettes stimulées avec de l’isoprénaline 10− 6 M, ce qui démontre que l’inhibition β-adrénergique provoquée par le thiopentone est physiologiquement importante. La dépression de l’oreillette provoquée par le thiopentone est identique à celle que produit la forskoline 10− 5 M comparativement à celle de l’isoprénaline 10− 6 M, ce qui indique que le thiopentone n’inhibe pas les récepteurs β-adrénergiques. Les auteurs concluent que le thiopentone déprime la fonction myocardique par plusieurs mécanismes qui impliquent l’inhibition de la cascade de l’adényl cyclase. L’inhibition du système se produit vraisemblablement au niveau de l’enzyme adényl cyclase; cependant, il est possible que d’autres éléments de la cascade de l’adényl cyclase soient impliqués.

Acidosis accentuates thiopental-induced myocardial depression in vitro

T he sensitivity pentobarbital suggests that of squid giant axons to blockade by is potentiated by acidosis, which the uncharged, membrane permeable for;is responsible for the pharmacologic effects (1). Since the pK, of thiopental is 7.6, minor changes in the blood pH of an animal or human patient could greatly alter the un-ionized fraction of thiopental available for pharmacologic action. The purpose of this study was to determine whether myocardial depression by thiopental is influenced by pH.

Relationship of cardiac muscle tension to Na+,K+-adenosine triphosphatase activity after chronic digitoxin administration in cats

Summary: To obtain a better understanding of the mechanism of action of the cardiac glycosides, we examined inotropic and biochemical effects of digitoxin in myocardium from cats chronically exposed to the drug. The mechanical function of papillary muscles was tested isometrically and left ventricular tissue was analyzed for Na+,K+-dependent adenosine triphosphatase ATPase activity. Muscles from control cat hearts developed tension at 2.5 ± 0.7 g/mm2; muscles from cats that received subcutaneous digitoxin—100 μg/kg on day 1, followed by 40 μg/kg/day for 4 days (group A), and 75 μg/kg on day 1, followed by 25 μg/kg/day for 9 days (group B)—developed significantly greater (p < 0.05) tension of 4.8 ± 0.3 and 3.6 ± 0.6 g/mm2, respectively. Further, in vitro maximal responsiveness to digitoxin was greater in the muscles from digitalized groups than in controls (p < 0.05): Muscles from control cats had a maximal response to in vitro addition of digitoxin of 3.5 ± 0.1 g/mm2; muscles from cats in group A reached 4.9 ± 0.3 g/mm2, and those from group B, 4.5 ± 0.7 g/mm2. Specific activity of microsomal Na+, K+ -ATPase from hearts of digitalized groups A and B was inhibited by 50–70% (p < 0.01). Developed tension, specific Na+,K+ -ATPase activity, and in vitro maximal responsiveness to digitoxin in a third group (C) of cats receiving the least daily digitoxin (75 μg/kg on day 1, followed by 15 μg/kg/day for 29 days) were not different from controls. Mean plasma digitoxin concentrations were 33, 16, and 3 ng/ml in groups A, B, and C, respectively. This report describes the simultaneous inhibition of Na+,K+ -ATPase activity and positive inotropic effect in hearts of animals chronically treated with a cardiac glycoside. It also shows that chronic in vivo administration of digitoxin has a greater effect on muscle tension than an acute in vitro addition of the drug.