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D L Roerig

Publications and source records attributed to D L Roerig.

At least 37 records · Page 2Linked to original sources
PubMed1996

Impact of angiotensin-converting enzyme substrate conformation on fractional hydrolysis in lung.

We examined the hydrolysis kinetics of benzoyl-phenylalanyl-glycyl-proline (BPGP) in the isolated perfused lung and in vitro for evidence of preferential hydrolysis of the trans isomer by angiotensin-converting enzyme (ACE). Nuclear magnetic resonance spectroscopy showed that BPGP exists as cis and trans isomers in a ratio of 44:56. After a single pass through the perfused rabbit lung over a wide range of infused BPGP concentrations, 42% of the BPGP was not hydrolyzed. In single-pass bolus-injection studies, 41% of the injected BPGP was not hydrolyzed, and very little further hydrolysis occurred in a second passage of the bolus through the lungs. In rat lung recirculation and in vitro studies of BPGP hydrolysis by ACE, approximately 60% of the substrate was hydrolyzed rapidly compared with the remaining approximately 40%, and the peptidyl-prolyl cis-trans isomerase cyclophilin increased the rate of the slower phase of the reaction in both kinds of experiments. We conclude that the rapid hydrolysis phase represents primarily the hydrolysis rate of the trans isomer and the slower phase the cis-trans isomerization rate, suggesting that the trans isomer of BPGP is preferentially hydrolyzed by ACE in the perfused lung and in vitro.

Animals↗
PubMed1995

Reduction of thiazine dyes by bovine pulmonary arterial endothelial cells in culture.

The uptake of methylene blue (MB), and toluidine blue O (TBO) by bovine pulmonary arterial endothelial cells grown on microcarrier beads was detected as a decrease in the concentration of dye in the medium after these thiazine dyes were added to the medium surrounding the cells. Because the reduced forms of these dyes are much more lipophilic than the oxidized forms, we considered the possibility that reduction of the dyes at the cell surface might have preceded the uptake by the cells. Therefore, we studied the ability of the cells to reduce a toluidine blue O-polyacrylamide polymer (TBOP), which was too large to enter the cells in either the oxidized or reduced form. The TBO moieties of the polymer were reduced by the cells, indicating that the dyes did not have to enter the cells to be reduced and that reduction can occur at, or near, the cell surface. The rate of TBOP reduction was about the same as the rate of uptake of the monomeric dyes, indicating that the cell surface reduction mechanism had a sufficient capacity to account for the monomer uptake by the cells. We also found that ferricyanide ion, which also did not permeate the cells, was reduced by the cells and that external ferricyanide inhibited the monomeric MB uptake. Thus the results with ferricyanide were also consistent with the concept that the monomeric thiazine dyes are reduced at the cell surface before the more lipophilic reduced forms are taken up by the endothelial cells.

Acrylic Resins↗
PubMed1995

Estimation of the pulmonary capillary transport function in isolated rabbit lungs.

Recently, we presented a method for estimating the pulmonary capillary volume and transport function based on the use of a reference indicator and two or more indicators that rapidly equilibrate (radially) with the tissue (i.e., the concentrations in the vascular and extravascular spaces at a given axial location are in equilibrium) during transit through the capillaries in a bolus-injection indicator dilution method (S. H. Audi, G. S. Krenz, J. H. Linehan, D. A. Rickaby, and C. A. Dawson. J. Appl. Physiol. 77:332-351, 1994). The objectives of the present study were 1) to determine whether [14C]diazepam and [3H]alfentanil equilibrate sufficiently rapidly between the vascular space and tissue and with sufficiently different pulmonary extra-vascular mean residence times to be used in a single bolus to estimate the pulmonary capillary volume and transport function using this method and 2) to estimate the pulmonary capillary volume and transit time distribution in isolated perfused rabbit lungs. Both [14C]diazepam and [3H]alfentanil were found to be rapidly equilibrating indicators by the criteria that, over a wide range of flow rates, their respective venous effluent concentration curves were nearly congruent on a time scale normalized to the lung mean transit time for the reference indicator (fluorescein isothiocyanate dextran). In addition, at a given plasma albumin concentration, [14C]diazepam had a significantly longer extravascular mean residence time than [3H]alfentanil, e.g., at 6% plasma albumin concentration, the extravascular mean residence time of [14C]diazepam was more than twice that of [3H]alfentanil. On average, the estimated pulmonary capillary volume for a 2.7-kg was approximately 4.2 ml or approximately 44% of the total pulmonary vascular volume (9.5 ml). The relative dispersion of the pulmonary capillary transport function of the rabbit was approximately 90%.

Alfentanil↗
PubMed1994

Reduction and accumulation of methylene blue by the lung.

We studied the disposition of methylene blue added to the perfusate passing through isolated perfused rabbit lungs. Experiments were carried out in a recirculating or single-pass mode, the latter with either a steady infusion or bolus injection of the dye in its blue oxidized form (MB+) or in its colorless reduced leukomethylene blue form (MBH). The recirculation experiments revealed that the dye was taken up by the lungs and that a substantial fraction (approximately 16%) of the MB+ entering the pulmonary artery was reduced before it emerged from the pulmonary veins. Sequestration of the dye by the lungs was a relatively slow process, and the blue color of the lungs at a time when there was little dye left in the perfusate suggests that much of the sequestered dye was in the oxidized form. The results from the single-pass bolus and steady infusion experiments suggest that MBH diffuses rapidly between perfusate and tissue and that it is more soluble in the tissue than in the perfusates used in the study. In this context, the concept of "solubility" includes the impact of the rapidly equilibrating associations of the dye with the perfusate albumin and tissue components. The observed characteristics of the disposition of the methylene blue within the lungs and the rapid rate of its reduction on passage through the lungs suggest that it may be useful to evaluate the possibility that changes in reduction, uptake, and/or sequestration rates may reflect alterations in the metabolic function of the lungs.

Animals↗
PubMed1993

Dexmedetomidine alters the hemodynamic effects of desflurane and isoflurane in chronically instrumented dogs.

BACKGROUND: Previous studies have shown that desflurane and isoflurane produce similar hemodynamic actions. This investigation examined the cardiovascular effects of desflurane and isoflurane in the presence or absence of dexmedetomidine, a highly selective alpha 2-adrenergic agonist that may be clinically useful as a premedicant or anesthetic adjuvant. METHODS: Four groups, comprising 40 experiments, were performed using ten dogs that were chronically instrumented for measurement of aortic and left ventricular pressure, the maximum rate of increase of left ventricular pressure (dP/dtmax), diastolic coronary blood flow velocity, cardiac output, and subendocardial segment length. On separate experimental days, systemic and coronary hemodynamics were recorded, and plasma concentrations of catecholamines were measured with or without oral dexmedetomidine pretreatment (30 micrograms/kg) in the conscious state and after 15 min of equilibration at 1.0, 1.3, and 1.6 end-tidal MAC desflurane or isoflurane in a random fashion. RESULTS: In conscious dogs, dexmedetomidine significantly decreased heart rate, cardiac output, percent segment shortening (%SS), left ventricular dp/dtmax, myocardial oxygen consumption (as estimated by the pressure-work index), and plasma norepinephrine concentration. Concomitant increases in systemic and diastolic coronary vascular resistance were observed. Pretreatment with dexmedetomidine decreased peak increases in heart rate during desflurane and isoflurane anesthesia. Mean arterial pressure was reduced less by desflurane than by isoflurane in the absence of dexmedetomidine. This difference was abolished in dogs pretreated with dexmedetomidine. Desflurane, but not isoflurane, decreased cardiac output in dexmedetomidine-pretreated dogs when compared with untreated dogs. Concomitantly, systemic vascular resistance was greater in desflurane- versus isoflurane-anesthetized dogs pretreated with dexmedetomidine. No differences in myocardial contractility, as assessed by left ventricular dP/dtmax and %SS, were observed between desflurane and isoflurane groups in the absence or presence of dexmedetomidine. CONCLUSIONS: The results indicate that the cardiovascular actions of desflurane or isoflurane are similar in the absence or presence of dexmedetomidine; however, some differences between anesthetic groups were noted. In the presence of dexmedetomidine, systemic vascular resistance during desflurane anesthesia was higher when compared with that during isoflurane anesthesia, indicating that desflurane produces less pronounced direct effects on peripheral vascular tone. The concomitant greater reductions in cardiac output are consistent with greater impedance to left ventricular outflow in desflurane-anesthetized dogs pretreated with dexmedetomidine, because no differences in contractile function were observed between volatile anesthetics. In contrast, cardiac output during isoflurane anesthesia after pretreatment with oral dexmedetomidine is better maintained secondary to the peripheral vasodilator actions of this agent.

Adrenergic alpha-Agonists↗
PubMed1993

Angiotensin-converting enzyme preferentially hydrolyzes trans isomer of proline-containing substrate.

An analysis of the hydrolysis kinetics of the synthetic angiotensin-converting enzyme (ACE) substrate benzoyl-phenylalanyl-alanyl-proline (BPAP) in the intact lung suggested that 12-15% of the BPAP was in a form that could not be hydrolyzed by ACE in the time course of a single pass through the lungs [C. A. Dawson et al. Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H853-H865, 1989]. BPAP has been found to exist as a mixture of cis and trans isomers in a ratio of approximately 14:86 in aqueous solution at equilibrium. Thus, one possible explanation for the incomplete hydrolysis of BPAP on passage through the intact lung is that the trans form is the preferred substrate for ACE. To examine this hypothesis, we measured BPAP hydrolysis by ACE in vitro over a range of ACE concentrations and in the presence and absence of the peptidyl-prolyl cis-trans isomerase cyclophilin. In the presence of a sufficient concentration of ACE and in the absence of cyclophilin, hydrolysis of [3H]BPAP by ACE followed biexponential progress curves, consistent with the hypothesis that the rate of hydrolysis of the majority (approximately 87%) of the substrate is proportional to ACE concentration, whereas the hydrolysis rate of the remaining substrate fraction is independent of enzyme concentration. The addition of cyclophilin resulted in an increase in the ACE-independent rate constant, an effect that was reversed by the cyclophilin inhibitor cyclosporin A. These results suggest that the enzyme-independent rate constant represents the rate of cis-trans isomerization and that the enzyme-dependent rate constant represents the hydrolysis of the trans isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Isomerases↗
PubMed1993

Halothane reduces release of adenosine, inosine, and lactate with ischemia and reperfusion in isolated hearts.

We investigated the protective effects of halothane on cardiac function of isolated hearts during global hypoperfusion and reperfusion by examining halothane's effects on altering coronary flow, myocardial oxygen utilization (MVO2), and release of adenosine (ADE), inosine (INO), and lactate (LAC). Isolated perfused guinea pig hearts were divided into three groups of perfusion at 25% (14 mm Hg), 10% (5.5 mm Hg), and 0% (no perfusion) from control perfusion pressure (PP, 55 mm Hg). Each of these PP groups was subdivided into three subgroups and perfused without halothane (control), with 0.23 +/- 0.01 mM (0.74%) halothane, or with 0.51 +/- 0.01 mM (1.65%) halothane. Halothane was present 10 min before reducing PP, during reduced PP (30 min), and for 10 min after reducing PP. Hypoperfusion was followed by 40 min of reperfusion at the control (100%, 55 mm Hg) PP. An additional group of control hearts was followed for the same period without reducing PP or perfusing with halothane. Exposure to 0.74% and 1.65% halothane, before reducing PP, decreased MVO2 and percent oxygen extraction (% O2E), but produced no significant change in coronary flow or release of ADE, ISO, or LAC. During early hypoperfusion (10 min) at 25% PP, 1.65% halothane significantly reduced release of ADE, INO, and LAC. During late hypoperfusion (40 min) the differences in LAC release diminished, but release of ADE and INO remained lower in the 1.65% halothane group. With early reperfusion there was a large increase in release of these metabolites, that was dependent on the decrease in perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1992

Clonidine reduces sympathetic activity but maintains baroreflex responses in normotensive humans.

Clonidine, an alpha 2-adrenergic agonist, has been shown to modify the hemodynamic responses to surgery. To examine further the mechanism underlying this action, we evaluated the neurocirculatory effects of oral clonidine and the ability of clonidine to alter the hemodynamic and sympathetic responses to a noxious stimulus (cold pressor test) and to baroreceptor perturbations in nine healthy men (ages 20-29 yr). Heart rate (ECG), blood pressure (radial artery catheter), central venous pressure (jugular vein), and cardiac output (impedance cardiography) were monitored before and after oral clonidine (0.3 mg) or placebo. Plasma norepinephrine was measured with high-performance liquid chromatography. Sympathetic nerve activity (SNA) to skeletal muscle blood vessels was recorded from a Tungsten needle positioned within the peroneal nerve. Baroreceptor testing was carried out by intravenous bolus injections of nitroprusside (100 micrograms) followed 60 s later by intravenous phenylephrine (150 micrograms). The slope of the linear relationship between the change in R-R interval versus the change in mean pressure (cardiac baroslope) or change in SNA versus change in diastolic pressure (sympathetic baroslope) was determined at baseline and 75 min after clonidine or placebo. In addition, peak responses to the cold pressor test (60-s hand immersion in ice water) were determined at the same intervals. Clonidine progressively decreased blood pressure and muscle SNA over the 75-min session. Clonidine subtly reduced the sympathoexcitation produced by the cold pressor test but did not alter the gain of the baroreceptor reflex regulating cardiac interval or peripheral SNA; baroslope relationships were simply shifted leftward (to operate at lower pressures).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1992

Use of blue dextran for measuring changes in perfused vascular surface area in lungs.

We investigated the uptake and efflux of Blue Dextran in the isolated perfused rabbit lung. Blue Dextran is a high-molecular-weight glucose polymer (original mol wt 2 x 10(6) g/mol) containing covalently bonded Reactive Blue 2 dye (approximately mmol/g dextran). This blue dye is known for its high binding affinity to a wide variety of proteins, with a particularly high affinity for serum albumin. In isolated rabbit lungs perfused with a protein-free perfusate, both bolus injection and recirculation of Blue Dextran revealed a rapid saturable uptake. Once the lungs were loaded with Blue Dextran, efflux of the Blue Dextran accumulated in the lungs could be induced by addition of bovine serum albumin (BSA) to the recirculating perfusate. The amount of BSA-induced efflux of Blue Dextran from the lung was independent of perfusate flow. When the left pulmonary artery was ligated after the lungs had been loaded with Blue Dextran, the dye-induced BSA efflux was only about 50% of normal. Release of the ligature so that both lungs were perfused resulted in efflux of the remaining Blue Dextran. The combination of high airway pressure and low flow also reduced the dye efflux, and the effect was reversed by reducing the airway pressure. With the assumption that the high average molecular weight of Blue Dextran confines this molecule to interaction with proteins on the vascular surface, the results of this study suggest that Blue Dextran uptake and its BSA-induced efflux are proportional to the perfused vascular surface area in the lung.

Animals↗
PubMed1992

Use of diazepam for interpreting changes in extravascular lung water.

Estimates of extravascular lung water volume (Qew) by use of the multiple indicator-dilution method with a hydrophilic indicator such as tritiated water, along with a vascular reference indicator, depend not only on tissue hydration but also on tissue perfusion. Separation of these effects might be facilitated if both hydrophilic and lipophilic indicators were used, with the assumption that the extravascular volume accessible to the lipophilic indicator would be independent of hydration. We found that in isolated perfused dog lung lobes the extravascular volume accessible to the lipophilic amine [14C]diazepam (Qed) was inversely proportional to the albumin concentration of the perfusate. This suggested that while the bolus was in the lungs, only a small fraction of the diazepam was in the aqueous phase of either lung tissue or perfusate. Changing the flow rate over a fairly wide range had little influence on the pattern of the tritiated water or [14C]diazepam effluent concentration curves when time was normalized to the lobar mean transit time. This suggests that the association of the diazepam with both the plasma albumin and the lipoid fraction of the tissue was in very rapid equilibrium on the time scale of a single pass through the lung lobe and that there was little barrier to its diffusion to and from the tissue. When the extravascular water volume was increased by either raising the hydrostatic pressure or instilling saline into the airways, both Qew and Qew/Qed increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1992

Influence of flow on pulmonary vascular surface area inferred from blue dextran efflux data.

Blue dextran (BD), which binds to proteins on the pulmonary endothelial surface and to plasma albumin, was used in isolated perfused dog lung lobe experiments to address the question: do changes in perfusate flow rate cause changes in perfused vascular surface area? When BD was added to a protein-free perfusate under zone 3 conditions at a high flow rate (15.8 +/- 0.7 ml/s), it was adsorbed by the endothelial surface. Then by changing the perfusate entering the lobe to an albumin-containing perfusate, the BD was eluted from the perfused surface by competitive binding to the perfusate albumin. The amount of BD eluted was measured in three experiments. In experiment 1, elution of the BD by the perfusate albumin was initiated after a balloon had been inflated within the lobar arterial tree to occlude a portion of the lobar vascular bed containing BD. Then the balloon was deflated, permitting albumin perfusate to perfuse the previously occluded part of the lobe. In experiment 2, BD elution began at a flow rate of 3 +/- 0.1 ml/s under zone 3 conditions and continued after the high-flow zone 3 conditions were reestablished. In experiment 3, the BD elution began at a flow rate of 4.2 +/- 0.7 ml/s under zone 2 conditions and continued after the high-flow zone 3 conditions were reestablished. Balloon inflation reduced the amount of BD recovered by 43%, demonstrating that a decrease in perfused vascular surface area could decrease BD recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The effects of the stereoisomers of the alpha 2-adrenergic agonist medetomidine on systemic and coronary hemodynamics in conscious dogs.

The alpha 2-adrenergic agonist medetomidine produces systemic hemodynamic effects that are mediated by both peripheral and central nervous system actions. The current investigation was designed to characterize coronary and systemic hemodynamic effects of the D- and L-stereoisomers of medetomidine in conscious, chronically instrumented dogs with and without autonomic nervous system blockade. Dogs were instrumented for measurement of aortic pressure, coronary blood flow velocity, cardiac output, left ventricular pressure, rate of change in pressure (dP/dt), and subendocardial systolic shortening. Administration of the D-isomer of medetomidine (doses of 1.25, 2.5, and 5.0 micrograms/kg, each administered over 10 min, with 60 min between doses) significantly altered systemic hemodynamics, in a biphasic fashion. A decrease in respiratory rate without change in arterial blood gas tensions occurred. With the 5 micrograms/kg dose of D-medetomidine, an initial pressor response was followed by secondary, significant (P less than 0.05), and dose-related decreases in heart rate (74 +/- 3 to 57 +/- 4 beats per min), mean arterial pressure (109 +/- 2 to 100 +/- 3 mmHg) and the rate-pressure product (10.5 +/- 0.4 to 7.0 +/- 0.5 beats.min-1.mmHg.10(3] accompanied by a reduction in plasma concentrations of norepinephrine. No changes in left ventricular end diastolic pressure or coronary blood flow velocity occurred. In contrast to the D-isomer, the L-isomer (1.25, 2.5 and 5.0 micrograms/kg) produced no changes in hemodynamics or plasma concentrations of norepinephrine. In dogs pretreated with hexamethonium (20 mg/kg), propranolol (2 mg/kg), and atropine methylnitrate (3 mg/kg) to produce autonomic nervous system blockade, D-medetomidine also produced an initial pressor response, but no secondary reduction in heart rate or arterial pressure occurred. The results indicate that the D-isomer of medetomidine is stereospecific for alterations in hemodynamics: the active D-isomer produces decreases in heart rate, arterial pressure, and the rate-pressure product via diminished sympathetic and/or augmented parasympathetic tone. This conclusion is supported by the absence of these changes after pharmacologic blockade of the autonomic nervous system.

Adrenergic alpha-Agonists↗
PubMed1991

Perfusate cytochrome c reduction in isolated rabbit lungs.

The reduction of ferricytochrome c within the perfusate in isolated lung perfusion systems has been demonstrated previously. We carried out the present study 1) to determine what reducing agents might be responsible for this reduction and 2) to determine whether the cytochrome c (cyto c) reduction within the recirculating perfusion system can be accounted for by relatively stable reducing agents released into the perfusate or whether some of the reduction is dependent on short-lived agents and/or proximity to the source of the agents within the lungs. Experiments were carried out with the use of isolated rabbit lungs perfused for 1 h in a recirculating system. In one group of experiments, ferricytochrome c was included in the recirculating perfusion system. In another group, the cyto c was added to produce the same concentration in samples after they were removed from a cyto c-free recirculating system. The recirculating cyto c was reduced at a rate of approximately 1.76 mumol/h, and approximately 22% was inhibitable by superoxide dismutase. Most of the rest could be inhibited by ascorbate oxidase within the recirculating perfusate. When the ferricytochrome c was added to the samples removed from the cyto c-free perfusion system, virtually the entire cyto c reducing capacity was inhibitable by ascorbate oxidase. Although reduced glutathione did accumulate in the recirculating perfusate, the quantity was not sufficient to have an important role in the cyto c reduction. We conclude that most of the cyto c reducing capacity within the lung perfusate could be accounted for by ascorbate released from the lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Chronic verapamil treatment depresses automaticity and contractility in isolated cardiac tissues.

Chronically administered verapamil can accumulate in cardiac tissues and may depress cardiac function despite low plasma concentration. To examine this, two groups of rabbits were injected intraperitoneally twice a day with either 1 mg/kg verapamil or saline for 28 days. Fourteen hours after the last dose, right atrial tissue and right ventricular papillary muscle were isolated. Plasma and myocardial tissue concentrations of verapamil were determined. Plasma samples contained no detectable amounts of verapamil, but the myocardium contained 2.1 +/- 0.6 (mean +/- SE) ng of verapamil per gram of wet tissue. Spontaneous action potentials recorded from the sinoatrial node in the verapamil-treated group showed decreases in the phase 0 and phase 4 depolarization rates, a slower pacemaker rate, and an attenuated response to epinephrine compared with the saline-treated group. Papillary muscle in the verapamil-treated group exhibited a significantly lower force of contraction and a depressed contractile response to epinephrine compared with the control group. There were no differences in rate or contractile responses the day after single injection with 2 mg/kg verapamil or saline twice a day. Myocardial verapamil concentration increased with the duration of treatment and with the doses given; myocardial verapamil concentration was 3.0 +/- 0.6 ng/g wet tissue in the group treated for 28 days with 2 mg/kg verapamil. Our study shows that chronic treatment of rabbits with verapamil decreases cardiac chronotropic and inotropic responses to adrenergic stimuli despite no detectable verapamil in plasma, and that accumulation of verapamil in the myocardium is probably associated with these effects.

Action Potentials↗
PubMed1990

Suppression of clinical weakness in experimental autoimmune encephalomyelitis associated with weight changes, and post-decapitation convulsions after intracisternal-ventricular administration of 6-hydroxydopamine.

Selective depletion of central nervous system norepinephrine (NE) by the neurotoxin 6-hydroxydopamine (6-OHDA) in rats subsequently inoculated with myelin basic protein (MBP) and complete Freund's adjuvant (CFA) produced experimental autoimmune encephalomyelitis (EAE) without the usual expected degree of weakness. The preservation of strength occurred in spite of continued weight loss. Post-decapitation myoclonic convulsive kick latency and kick number, which are known to depend on spinal cord NE, agreed well with the degree of weakness through the clinical disease course. The only difference between EAE groups was that the stronger 6-OHDA pretreated EAE animals did not have an elevated pons-medulla NE compared to saline intracisternal-ventricular (i.c.v.) pretreated controls. We conclude that 6-OHDA can influence the clinical course of weakness by interfering with central noradrenergic activity independent of other features associated with disease in EAE. This effect of 6-OHDA may be exerted through alteration of the blood-spinal cord barrier function and/or central nervous system blood flow.

Animals↗
PubMed1990

Lung angiotensin-converting enzyme kinetics from indicator-dilution and constant-infusion methods.

We compared the results of three methods used to evaluate the kinetics of benzoyl-phenylalanyl-alanyl-proline (BPAP) hydrolysis by angiotensin-converting enzyme in the isolated rabbit lung. In method A, the arteriovenous concentration differences at each of four rates of BPAP infusion were used to determine the effect of concentration on the rate of BPAP hydrolysis. In methods B1 and B2, trace doses of [3H]BPAP were injected during each constant infusion of unlabeled BPAP so that the venous [3H]BPAP concentration could be used to estimate the venous BPAP concentration and the rate of hydrolysis at each background concentration. In method C, three boluses containing different amounts of unlabeled BPAP as well as tracer [3H]BPAP were injected such that each bolus resulted in a range of concentrations and hydrolysis rates that could be estimated from the venous concentrations of [3H]BPAP. Each method provided the data needed to calculate the maximum uptake rate (Vmax) and Km, the concentration at half Vmax, assuming that the hydrolysis can be represented by the Michaelis-Menten equation. However, the mathematical model underlying each method involved different assumptions about the effects of heterogeneity of capillary transit times and bolus dispersion. The mean values of Vmax were 180, 216, 217, and 200 nmol/s and for Km 7.8, 10.4, 8.6, and 10.0 microM for methods A, B1, B2, and C, respectively. The differences between methods were not statistically significant. These results suggest that theoretical differences between the methods did not have a quantitatively important impact relative to other factors contributing random errors to each of the methods. The choice between methods can therefore be made on practical grounds.

Animals↗
PubMed1990

Presynaptic modulation of ganglionic ACh release by muscarinic and nicotinic receptors.

The present experiments were undertaken to investigate the effects of atropine and d-tubocurarine on acetylcholine (ACh) release and ganglionic synaptic transmission in the isolated cat stellate ganglion. Ganglionic release of picomole amounts of ACh was measured by radioenzymatic assay, and ganglionic transmission was estimated on the basis of the compound action potential recorded from the postganglionic stellate cardiac nerve. Atropine (5 microM) produced a significant increase in both spontaneous and evoked ACh release from the ganglion while depressing synaptic transmission. d-Tubocurarine (20 microM) also caused a significant, though smaller, increase in spontaneous release of ACh but had little effect on evoked release of ACh. These results suggest that ACh release and synaptic transmission in the cat stellate ganglion are subject to cholinergic feedback regulation, which appears to be mediated predominantly via muscarinic presynaptic receptors.

Acetylcholine↗