Ervin E. Bagwell

Stereoselective delivery and actions of beta receptor antagonists

These studies have revealed that the delivery and actions of beta receptor antagonist drugs are controlled by a cascade of stereoselective processes involving multiple enzymes, transport proteins and receptors. In essence, the free concentration of the pharmacologically active (-)-enantiomer species of these drugs presented to cell surface beta receptors appears to be a function of the stereoselective clearance by hepatic cytochrome P-450 isoenzymes, enantiomer selective binding to alpha 1-acid glycoprotein and albumin and perhaps predominantly by stereoselective sequestration (and release) by the vesicular amine transport protein within adrenergic neurons. Stereoselectivity in the clearance of beta blocking drugs, which can favor either the (+)- or (-)-enantiomer, only appears to be important for the lipophilic drugs which are cleared by hepatic metabolism. Such stereoselectivity is due to differential stereochemical substrate requirements of individual hepatic cytochrome P-450 isoenzymes. Interindividual variations in the stereoselectivity can occur as a result of differences in the amount and expression of cytochrome P-450 isoenzymes due to genetic predisposition or other factors. In the same context, we have observed a significant correlation between the extent and stereoselectivity of binding of beta blocking drugs to plasma proteins. This is another finding which suggests that variability in the expression of individual proteins involved in the beta blocking drug-protein cascade determines the free concentration of the pharmacologically active enantiomer. However, since most observations have been made in young normal subjects, the extent of stereoselectivity in metabolism, binding and other processes is unknown in the general population where steady-state plasma concentrations can vary widely due to multiple biological factors. The observations from neural studies support the concept that adrenergic nerve endings provide a depot for the stereoselective storage and release of the active enantiomer of beta receptor antagonists. The mechanism of this release appears to involve exocytotic secretion of drug that has been stereoselectively accumulated by the neurotransmitter storage vesicles. In terms of this idea, beta receptor antagonists released during nerve stimulation may achieve concentrations of the (-)-enantiomer within the adrenergic synapse greatly in excess of those found in plasma. Such a mechanism could significantly influence both the intensity and duration of beta receptor blockade in the heart, blood vessels, brain and other target tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Circulating epinephrine and norepinephrine in coronary occlusion

Abstract 1. 1. Following experimental coronary occlusion in thirty-nine dogs, mean values of norepinephrine increased maximally from 1.6 to 10.5 μg-/L. of plasma in thirty-three surviving animals. Serum transaminase increments paralleled norepinephrine elevations in most instances. No changes occurred in circulating levels of epinephrine. Recordings of fluorescence emission spectrums aided in the identification and quantitation of the catecholamines. 2. 2. Essentially the same results occurred in four chronically adrenalectomized dogs. 3. 3. Following coronary occlusion and the administration of a sympatholytic agent (tri-methyl-2-2,6 xylyloxy-propyl ammonium chloride monohydrate), elevated circulating levels of norepinephrine declined progressively to pre-occlusion figures. 4. 4. Of eighteen dogs treated with reserpine, eleven survived the occlusive procedure and showed increments in norepinephrine and transaminase similar to those of the untreated animals, 5. 5. The catecholamine content of the infarct and the adjacent area was not elevated above the values found in normal tissue.

Limitation of Myocardial Function by Reduced Coronary Blood Flow during Isoproterenol Action

The interpolated decrease in heart force or isometric systolic tension that occurs during isoproterenol stimulation has been examined in terms of changes in coronary flow and myocardial metabolism. In 67 open-chest dogs under pentobarbital anesthesia, determinations were made of lactate, pyruvate, Po2 and Pco2 in arterial and coronary sinus blood; coronary flow was measured with an electromagnetic flow transducer and ventricular force with a strain gauge arch. Although the characteristic, uncomplicated effect of isoproterenol is a marked increase in coronary flow and contractile force, this is briefly interrupted by a sharp decrease in these functions, and the decrease is associated with evidence of anaerobic metabolism. This decrease is concomitant with decreased coronary perfusion pressure and is intensified by sustained infusion of isoproterenol or by lowered oxygen concentrations in the inspired air. The stage of depressed function is counteracted by mechanical maintenance of high aortic pressure or by slow, controlled heart rate. When uncontrolled, tachycardia due to isoproterenol continues without phasic interruption. The intermediate period of depressed function is interpreted in terms of sharply decreased oxygen delivery when both cardiac rate and force are increased. The hemodynamic and metabolic values for these acutely occurring, reversible extremes have been specified.

Determination of blood halothane levels by gas chromatography

SummaryA method of isolation by distillation of halothane from blood and its subsequent Chromatographic detection and quantitation have been described. The method is simple, rapid, and inexpensive. It lends itself well to incorporation into anaesthetic investigations when blood (and tissue) anaesthetic levels must be obtained In serial manner.The accuracy of the method, based on tests of reproducibility and recovery, is within ±5 per cent. These data are not of a selected nature and represent a testing of the isolation and Chromatographic techniques for quantitative analytical adequacy.Some data obtained from animal experiments are presented. Detailed correlation of these data with cardiovascular and acid-base investigations will appear elsewhere.13RésuméNous avons décrit une méthode d’identification de l’halothane par sa distillation du sang et sa détection chromatographique subséquente et son titrage. La méthode est simple, rapide, peu coûteuse. Elle peut être entreprise aussi bien avec d’autres investigations anesthésiques quand les niveaux d’anesthésie dans le sang et dans les tissus doivent être obtenus en série.La précision de cette méthode basée sur des tests de reproduction et de réveil est de +5 pour cent. Ces valeurs ne sont pas de nature sélective et elles représentent un test d’identification et de technique chromatographique pour une analyse quantitative adéquate.Nous avons présenté quelques données obtenjues des expériences sur des animaux. Nous publierons ailleurs la corrélation detaillée entre ces notions et des investigations sur l’équilibre acide-base et sur le système cardiovasculaire.

Sequential use of detergents for solubilization and reconstitution of a membrane ion transporter

Solubilization and reconstitution of the cardiac sarcolemmal Na+/Ca2+ exchanger by use of the anionic detergent cholate and its application for reconstitution of the exchanger following solubilization with zwitterionic or nonionic detergents is described. Solubilization and reconstitution with cholate provided a 32.6-fold enrichment of Na+/Ca2+ exchange activity over sarcolemmal vesicles (5.2 to 170 nmol/mg/s) with 202% recovery of total activity. In combination with asolectin, the cholate dilution technique (H. Miyamoto and E. Racker, J. Biol. Chem. 255, 2656, 1980) offers a rapid and simple means for reconstitution and provides good recovery of total and specific Na+/Ca2+ exchange activity. However, the use of anionic detergents for solubilization precludes the use of certain chromatographic procedures for protein purification. Conversely, nonionic and zwitterionic detergents permit effective use of available chromatographic techniques, but can be troublesome during reconstitution. We have combined the advantages of solubilization with nonionic and zwitterionic detergents with the advantages of reconstitution by cholate dilution. Reconstitution of the exchanger, after solubilization with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate (Chaps) or n-octyl-beta-D-glucoside, was accomplished by the addition of a cholate/asolectin medium followed by dilution. Na+/Ca2+ exchange activity was enriched 30.7-fold with 196% recovery with Chaps and 34.1-fold with 204% recovery with n-octyl-beta-D-glucoside. The presence of Chaps was found to shift the optimal asolectin concentration for reconstitution from 15 mg/ml (cholate alone) to 25 mg/ml. In addition, pelleting of proteoliposomes subsequent to reconstitution resulted in greatest recovery of total activity when volumes were kept below 1.0 ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium and potassium permeability of membrane vesicles in a sarcolemma-enriched preparation from canine ventricle

SummaryVesicles in a highly enriched sarcolemma preparation from canine ventricle were found to develop membrane potentials in response to outwardly directed potassium and inwardly directed sodium concentration gradients. The magnitude of the potential measured by the fluorescent dye diS−C3-(5) suggested a sodium-to-potassium permeability ratio between 0.2 and 1.0 which is one to two orders of magnitude greater than values obtained for the myocardial cell. Radiotracer techniques were employed to evaluate the permeability coefficients of the isolated cardiac sarcolemma membrane for sodium and potassium under equilibrium conditions (i.e., equal salt concentrations in the intravesicular and extravesicular spaces). The uptake of sodium and potassium was best described by two exponential processes which followed an increment of uptake that occurred prior to the earliest assay time (i.e., 17 sec). The compartment sizes were linear, nonsaturable functions of the cation activity. Evaluation of the rate coefficients of cation uptake by the two exponential processes versus cation activity revealed that sodium influx via the slow process and potassium influx via the fast process varied linearly with cation activity, suggesting that the permeability coefficients were concentration independent for these compartments. Conversely, sodium influx via the fast process exhibited a nonlinear increase with increasing sodium activity, and potassium influx via the slow process appeared to saturate with increasing potassium activity. In general, the permeabilities of the sarcolemma-enriched preparation for sodium and potassium were of equal magnitude. The permeability coefficients were lower than that for the potassium coefficient reported for cardiac cells but are in the range of that reported for sodium.

Myocardial contractility during induction and steady-state ketamine anesthesia.

ETAMIhE has been shown to be an effecK tive s hort-acting anes thes t ic agent without significant respiratory or cardiovascular depre3sive action.lS3 The cardiovascular response to anesthesia with this agent is usually characterized by increased arterial blood pressure, cardiac output, and heart rate.3 The increase in heart rate has been attributed t.1 a vagolytic action of ketamine, since it has been reported that atropine attenuates tb is response.3 Additionally, the increase in cardiac output and arterial pressure is reduced by pretreatment with atropine.3 These findings have led to the suggestion that ketamine does not produce myocardial depression. Further, studies in which the initial ventricular impulse or left ventricular dpldt maximum was measured indicated no myocardial depression.3.4 However, investigations using isolated cardiac muscle preparations have demonstrated a reduction of contractile activity following addition of ketamine to the bath.4-6 I t has been suggested that myocardial depression is due to the ketamine concentrations in the muscle bath being higher than those obtained in the blood of intact animals.

Blood levels and cardiovascular dynamics during fluroxene anaesthesia in dogs

SummaryA gas chromatographic technique has been described which allows the quantitative measurement of blood and vapour concentrations of trifluoroethylvinyl ether (fluroxene). Using this method, arterial and venous blood levels of fluroxene were measured during increasing inspired concentrations of the agent, and correlated with concurrent changes in circulatory dynamics.During light levels of anaesthesia (6.0 per cent) arterial and venous concentrations of fluroxene were 32 and 26 mg./100 ml. respectively. At this time there was minimal depression of the cardiovascular system. When the inspired concentration was increased there was progressive depression of aortic pressure, ventricular contractile force, aortic flow, and calculated stroke volume. Heart rate was not significantly altered until deep levels of anaesthesia were obtained. Calculated peripheral resistance was not significantly altered, and it is felt that this, along with the depression of contractile force, indicates that myocardial depression plays a primary role in the over-all circulatory depression occurring during deep levels of fluroxene anaesthesia.In the animals in which anaesthesia was induced with thiopental and maintained with fluroxene for two hours, there was only minimal depression of the cardiovascular system. Most of the observed depression occurred during the thiopental induction, and maintenance with fluroxene failed to produce any further depression.RésuméOn a utilisé une technique chromatographique pour l’analyse quantitative des concentrations de fluroxène (Fluoromar). On a mesuré les niveaux de fluroxène dans le sang artériel et dans le sang veineux durant différents degrés d’anesthésie, et on les a mis en corrélation avec les changements dans la dynamique circulatoire.Durant l’anesthésie légère, il y eut peu de dépression circulatoire (6.00%). En augmentant la concentration de mélange inspiré, une dépression progressive de la pression aortique, de la force de contraction ventriculaire, du courant aortique et du débit systolique s’est produite en même temps qu’augmentait le niveau sanguin de l’anesthésique. La vitesse du pouls n’a pas changé tant qu’on n’a pas atteint une anesthésie profonde. Quelle que fut la profondeur de l’anesthésie, la résistance périphérique n’a pas varié sensiblement. Ces observations, en plus de la dépression de la contractilité du myocarde, indiquent que la dépression du myocarde joue un rôle de premier plan dans la dépression circulatoire générale observée.

Effects of Reserpine on Adrenal Responses to Nicotine.

Summary Increments in plasma levels of epinephrine resulting from nicotine stimulation of the adrenal medulla are markedly reduced by reserpine. However, increments in heart contractile force and arterial blood pressure produced by adrenal stimulation, normally proportional to catechol amine levels, are not significantly altered following reserpine.

Evidence that phentolamine acts centrally to increase the contractile force of the heart

Abstract In an attempt to localize the site of phentolamines positive inotropic effect, the sympathetic nervous system was interrupted at the ganglia, entire spinal cord, or at the level of the first cervical vertebrae. In each case phentolamine failed to elicit a positive inotropic effect, and instead decreased heart force and rate. This indicates that the site of action is mediated in a supraspinal area. Preparations utilizing a cross-perfused technique in which the circulation to the recipient animals head was isolated were used to determined the actions of phentolamine on the brain. In the recipient animal heart force increased significantly with only minimal changes in heart rate and aortic blood pressure. This indication of a central site of action was further defined by removing the influences of all tissue anterior to the superior colliculus. This procedure had very little effect of phentolamines cardiovascular action which points to a brain stem site of action.