Effects and mechanism of action of aminophylline on cardiac function and regional blood flow distribution in conscious dogs

Microwave-assisted reactions: Efficient and versatile one-step synthesis of 8-substituted xanthines and substituted pyrimidopteridine-2,4,6,8-tetraones under controlled microwave heating

We report herein a simple and efficient one-step synthesis of 8-substituted xanthines and substituted pyrimidopteridine-2,4,6,8-tetraones via reaction of 1,3-dimethyl-5,6-diaminouracil 1 with activated double bond systems 2 assisted by controlled microwave irradiation. The obtained heterocycles are privileged biologically relevant scaffolds.

Elucidating the interaction of aminophylline with calf thymus DNA using multispectroscopic and molecular docking approach

Aminophylline (Am) is a methylxanthine compound clinically applied for chronic lung diseases like asthma, bronchitis or emphysema. Chemically, it comprises theophylline and ethylenediamine in a ratio 2:1. For the widening of the therapeutic window of any class of drug or for the designing of the newer therapeutic compound, an insight into the binding mechanics of available drugs with DNA is quite imperative. In view of that, here in this study we have investigated binding mechanics of aminophylline molecule with calf thymus DNA (Ct-DNA) using various spectroscopic techniques as well as molecular docking approach. Spectral analysis employing UV-visible and fluorescence approach confirmed the formation of aminophylline-Ct-DNA complex. The binding constant was calculated as 3.5 × 10⁴ M^-1 with 0.90 as the value of binding site suggestive of minor groove binding mode of aminophylline. The groove binding mode was further confirmed through spectrofluorimetric experiments like competitive displacement assay employing ethidium bromide, hoechst and rhodamine 6 G dyes as well as iodide quenching studies. The circular dichroic spectral evaluation and molecular docking study finally validated the minor groove binding mode of aminophylline with binding energy calculated as -4.5 Kcal/mol.

Xanthine scaffold: scope and potential in drug development

Medicinal plants have been the basis for discovery of various important marketed drugs. Xanthine is one such lead molecule. Xanthines in various forms (caffeine, theophylline, theobromine, etc) are abode in tea, coffee, cocoa, chocolate etc. giving them popular recognition. These compounds are best known for their diverse pharmaceutical applications as cyclic nucleotide phosphodiesterase inhibition, antagonization of adenosine receptor, anti-inflammatory, anti-microbial, anti-oxidant and anti-tumor activities. These properties incentivize to use xanthine as scaffold to develop new derivatives. Chemical synthesis contributes greater diversity in xanthine based derivatisation. With highlighting the existing challenges in chemical synthesis, the present review focuses the probable solution to fill existing lacuna. The review summarizes the available knowledge of xanthine based drugs development along with exploring new xanthine led chemical synthesis path for bringing diversification in xanthine based research. The main objective of this review is to explore the immense potential of xanthine as scaffold in drug development.

A Double-Blinded, Randomized, Placebo-Controlled Clinical Trial of Aminophylline to Prevent Acute Kidney Injury in Children Following Congenital Heart Surgery With Cardiopulmonary Bypass

OBJECTIVES

Acute kidney injury occurs commonly in children following congenital cardiac surgery with cardiopulmonary bypass and has been associated with increased morbidity and mortality. Aminophylline, a methylxanthine nonselective adenosine receptor antagonist, has been effective in the management of acute kidney injury in certain populations. This study sought to determine whether postoperative administration of aminophylline attenuates acute kidney injury in children undergoing congenital cardiac surgery with cardiopulmonary bypass.

DESIGN

Single-center, double-blinded, placebo-controlled, randomized clinical trial.

SETTING

Tertiary center, pediatric cardiovascular ICU.

PATIENTS

A total of 144 children after congenital heart surgery with cardiopulmonary bypass.

INTERVENTIONS

Seventy-two patients were randomized to receive aminophylline and 72 patients received placebo. Study drug was administered every 6 hours for 72 hours.

MEASUREMENTS AND MAIN RESULTS

The primary outcome variable was the development of any acute kidney injury, defined by the serum creatinine criteria of the Kidney Diseases: Improving Global Outcomes. Secondary outcomes included the development of severe acute kidney injury, time between cardiovascular ICU admission and first successful extubation, percent fluid overload, total fluid balance, urine output, bioelectrical impedance, and serum neutrophil gelatinase-associated lipocalin. The unadjusted rate and severity of acute kidney injury were not different between groups; 43 of 72 (60%) of the treatment group and 36 of 72 (50%) of the placebo group developed acute kidney injury (p = 0.32). Stage 2/3 acute kidney injury occurred in 23 of 72 (32%) of the treatment group and 15 of 72 (21%) of the placebo group (p = 0.18). Secondary outcome measures also demonstrated no significant difference between treatment and placebo groups. Aminophylline administration was safe; no deaths occurred in either group, and rates of adverse events were similar (14% in the treatment group vs 18% in the placebo group; p = 0.30).

CONCLUSIONS

In this placebo-controlled randomized clinical trial, we found no effect of aminophylline to prevent acute kidney injury in children recovering from cardiac surgery performed with cardiopulmonary bypass. Future study of preoperative aminophylline administration to prevent acute kidney injury may be warranted.

Impact of aminophylline on the pharmacodynamics of propofol in beagle dogs

This study aimed to characterize pharmacodynamic interaction between propofol and aminophylline. Nine beagle dogs were randomly allocated at the propofol rates of 0.75 (group A), 1.00 (group B), and 1.25 (group C) mg/kg/min. During period 1, propofol only was infused, while during period 2, aminophylline only, at the rate of 0.69 (group A), 1.37 (group B), and 2.62 (group C) mg/kg/h. During periods 3-5, the two drugs were co-administered. The aminophylline infusion rate was 0.69 (period 3), 1.37 (period 4), and 2.62 (period 5) mg/kg/h. The aminophylline was infused from 0 to 30 h, and the propofol was infused at 24 h for 20 min. Blood samples and electroencephalograms were obtained at preset intervals. In the linear regression between log-transformed doses of aminophylline and AUC inf, the slope was 0.6976 (95% CI 0.5242-0.8710). Pharmacokinetics of aminophylline was best described by a one-compartment, with enzyme auto-induction, model. Pharmacokinetics and pharmacodynamics of propofol were best described by a three-compartment model and a sigmoid Emax model, respectively. Pharmacodynamic parameter estimates of propofol were: k(e0) = 0.805/min, E0 = 0.76, Emax = 0.398, Ce(50 na) = 2.38 μg/mL (without aminophylline-exposure), C(e50 wa) = 4.49 μg/mL (with aminophylline-exposure), and γ = 2.21. Propofol becomes less potent when exposed to aminophylline. Pharmacodynamic antagonistic interaction of aminophylline with propofol sedation, may occur, not in a dose-dependent manner, but in an all-or-none response.

Comparison of the recovery and respiratory effects of aminophylline and doxapram following total intravenous anesthesia with propofol and remifentanil

STUDY OBJECTIVE

To compare the effects of aminophylline and doxapram on recovery, respiration, and bispectral index (BIS) values in patients after total intravenous anesthesia (TIVA) with propofol and remifentanil.

DESIGN

Prospective, randomized, blinded clinical trial.

SETTING

Operating room of a university hospital.

PATIENTS

90 adult, ASA physical status 1 and 2 patients scheduled for elective laparoscopic vaginal hysterectomy.

INTERVENTIONS

TIVA was performed with the induction target of remifentanil 3 ng/mL and propofol 6 μg/mL, followed by the maintenance target of remifentanil 1-3 ng/mL and propofol 3-5 μg/mL at the effect site, and with BIS scores in 40-50 range. Patients were randomized to three groups to receive intravenous (IV) aminophylline 3 mg/kg (n = 30), IV doxapram 1 mg/kg (n = 30), or normal IV saline (control; n = 30).

MEASUREMENTS AND MAIN RESULTS

After administration of the study drugs, return to spontaneous ventilation differed significantly among the three groups. The times to eye opening and hand squeezing on verbal command were similar. The time to extubation was shortened in both the doxapram and aminophylline groups (P < 0.05). Tidal volumes were increased in the doxapram group at 5-14 minutes and the aminophylline group at 5-12 minutes (P < 0.05). Respiratory rates were increased at 2 to 8 minutes and then showed a decrease at the 12 to 14-minute mark in both the doxapram and aminophylline groups (P < 0.05). No difference was noted between the two groups. BIS values were increased in both the doxapram and aminophylline groups at 4-10 minutes (P < 0.05). Heart rates were increased in the doxapram group for the first 8 minutes and at 1-2 minutes in the aminophylline group (P < 0.05).

CONCLUSION

Aminophylline 3 mg/kg or doxapram 1 mg/kg shortened the time to spontaneous ventilation and improved early recovery from TIVA without appreciable side effects. The more rapid emergence correlates with higher BIS values when compared with the saline control group. The arousal and respiratory effects of aminophylline were comparable to those of doxapram.

The cardiovascular effects of methylxanthines

In the concentration range that is normally achieved in humans, e.g., after the drinking of coffee or in patients treated with theophylline, the cardiovascular effects of methylxanthines are primarily due to antagonism of adenosine A(1) and A(2) receptors. Inhibition of phosphodiesterases or mobilization of intracellular calcium requires much higher concentrations. In conscious humans, acute exposure to caffeine results in an increase in blood pressure by an increased total peripheral resistance, and a slight decrease in heart rate. This overall hemodynamic response is composed of direct effects of caffeine on vascular tone, on myocardial contractility and conduction, and on the sympathetic nervous system. Caffeine is the most widely consumed methylxanthine, mainly derived from coffee intake. Regular coffee consumption can affect various traditional cardiovascular risk factors, including a slight increase in blood pressure, an increase in plasma cholesterol and homocysteine levels, and a reduced incidence of type 2 diabetes mellitus. Although most prospective studies have not reported an association between coffee consumption and coronary heart disease, these findings do not exclude that the acute hemodynamic and neurohumoral effects of coffee consumption could have an adverse effect in selected patient groups who are more vulnerable for these effects, based on their genetic profile or medication use.

The effect of aminophylline on loss of consciousness, bispectral index, propofol requirement, and minimum alveolar concentration of desflurane in volunteers

BACKGROUND

Adenosine is a soporific neuromodulator; aminophylline, which is clinically used as a bronchodilator, antagonizes the action of adenosine in the central nervous system. Thus, we tested the hypothesis that aminophylline delays loss of consciousness (LOC) and speeds recovery of consciousness (ROC) with propofol anesthesia, and that aminophylline increases the minimum alveolar concentration (MAC) of desflurane.

METHODS

In this double-blind crossover study, volunteers were randomized to either aminophylline or saline on different days. Aminophylline 6 mg/kg was given IV, followed by 1.5 mg x kg(-1) x h(-1) throughout the study day. After 1 h of aminophylline or saline administration, propofol 200 mg was given at a rate of 20 mg/min. The bispectral index was continuously monitored, as were times to LOC and ROC. After recovery from propofol, general anesthesia was induced with sevoflurane and subsequently maintained with desflurane. The Dixon "up-and-down" method was used to determine MAC in each volunteer after repeated tetanic electrical stimulation.

RESULTS

Eight volunteers completed both study days. Time to LOC was prolonged by aminophylline compared with saline (mean +/- SD) (7.7 +/- 2.03 min vs 5.1 +/- 0.75 s, respectively, P = 0.011). The total propofol dose at LOC was larger with aminophylline (2.2 +/- 0.9 vs 1.4 +/- 0.4 mg/kg, P = 0.01), and the time to ROC was shorter (6.18 +/- 3.96 vs 12.2 +/- 4.73 min, P = 0.035). The minimum bispectral index was greater with aminophylline (51 +/- 15 vs 38 +/- 9, P = 0.034). There was no difference in MAC.

CONCLUSION

Aminophylline decreases the sedative effects of propofol but does not affect MAC of desflurane as determined by tetanic electrical stimulation.

Effect of aminophylline on bispectral index

BACKGROUND

The aim of the present study was to investigate the effects of aminophylline on BIS as well as clinical recovery in patients anesthetized with sevoflurane.

METHODS

Sixty patients with status of ASA I-II scheduled for elective surgery were enrolled in this study. Anesthesia was induced by 2 mg kg(-1) of propofol and 0.5 mg kg(-1) of atracurium, maintained with 1:1 ratio of oxygen and nitrous oxide and 2-2.5% sevoflurane, keeping BIS values at 50 +/- 5. During the last 30 min of the operation no muscle relaxant was given and anesthesia was continued without decreasing anesthetic concentration. After sevoflurane discontinuation, saline was given to Group P, and 5 mg kg(-1) of aminophylline was given to Group A. Bispectral index values, heart rate, blood pressure and oxygen saturation were determined in all the patients before and every min after injection of the test drug for 15 min. The following variables were measured in both groups: eye opening, extubation time, response to command, Aldrete scores, and performing three simple arithmetic calculations.

RESULTS

Between groups there was no statistically significant difference in mean arterial blood pressure, SpO2 and anesthesia time. Heart rate was found to be statistically higher (P < 0.001) at 2 to 6 min in Group A when compared with group P. Eye opening, verbal response, extubation and arithmetic calculation times were significantly shorter (P < 0.001) in Group A. Bispectral index scores were significantly higher in Group A at 1 to 12 min after aminophylline injection when compared with placebo (P < 0.001).

CONCLUSION

Recovery from sevoflurane anesthesia and BIS scores are improved in early period when aminophylline is given at emerging from anesthesia.

Myocardial perfusion imaging findings and the role of adenosine in the warm-up angina phenomenon

OBJECTIVES

This study examined the roles of myocardial perfusion and adenosine in warm-up angina.

BACKGROUND

In warm-up angina, neither the role of an adenosine-mediated mechanism, as is found in experimental ischemic preconditioning, nor of increased myocardial perfusion is well defined.

METHODS

In substudy A, a single-photon emission computed tomography (SPECT)-thallium-201 exercise test was performed by 12 subjects with ischemic heart disease on three occasions one week apart. The third test was preceded by a warm-up test. The extent of the thallium deficit and its intensity on the third test were compared with the baseline tests controlling for the heart rate-systolic blood pressure product (RPP) at thallium injection. In substudy B, 12 similar subjects did two successive exercise tests at two separate sessions and received the adenosine antagonist, aminophylline (intravenous 5 mg/kg bolus and 0.9 mg/kg/h infusion) at one session, and equivalent saline at the other session. Change in ischemic threshold (RPP at 1 mm ST segment depression) and in maximum ST depression adjusted for RPP were analyzed.

RESULTS

In substudy A, despite a significant attenuation of electrocardiogram indexes of myocardial ischemia between the baseline and third (warmed-up) tests, the thallium extent deficits (20.8 +/- 15.1% and 16.8 +/- 12.4%) and intensity deficits (41.2 +/- 12.6% and 39.3 +/- 12.6%) did not differ significantly. In substudy B, the increase in ischemic threshold on re-exercise was unaffected by aminophylline. Adjusted maximum ST depression even decreased to a greater extent on re-exercise with aminophylline (by 51 +/- 21%) than with saline (by 32 +/- 19%) (p = 0.012).

CONCLUSIONS

While warm-up angina is associated with a significant attenuation of exercise electrocardiogram indexes of ischemia, it is unaccompanied by significant changes in SPECT perfusion and does not appear to be mediated by an adenosine-dependent mechanism since it is not blocked by aminophylline. Thus, its mechanism, which appears distinct from experimental ischemic preconditioning, remains unidentified.

Beneficial Effects of Aminophylline on Ischemia-Reperfusion in Isolated Rabbit Heart

Eighteen rabbit hearts were arrested for 3 hours with cardioplegic solution at 4°C, followed by reperfusion with oxygenated perfusion solution at 37°C for 2 hours. Six control hearts received no drug during arrest or reperfusion (group 1). Six hearts received 3 mg·L−1 aminophylline during the arrest period (group 2). Six hearts received 3 mg·L−1 aminophylline during the reperfusion period (group 3). Effects of aminophylline were evaluated in terms of the pressure-volume relationship, coronary flow, myocardial oxygen extraction, and lactate release before cardioplegic arrest and after 1 and 2 hours of reperfusion. End-diastolic pressure at constant volume after 2 hours of reperfusion was 19 ± 2.63 mm Hg in group 1, 14 ± 1.7 mm Hg in group 2, and 19 ± 2.55 mm Hg in group 3 (p < 0.05 for group 2 versus groups 1 and 3). End-systolic pressure at constant volume after 2 hours of reperfusion was 81 ± 3.55 mm Hg in group 1, 90 ± 2.95 mm Hg in group 2, and 84 ± 3.47 mm Hg in group 3 (p < 0.05 for group 2 versus groups 1 and 3). Oxygen extraction was significantly higher and release of lactate was significantly lower in group 2 compared to groups 1 and 3. The results indicate that aminophylline administration during cardioplegic arrest improved systolic and diastolic function and had a beneficial effect on metabolic recovery.

Effects of adrenergic and nitrergic blockade on theophylline-induced increase in peripheral blood flow in rat ear

A bolus injection of theophylline produced a significant increase in peripheral blood flow in anesthetized rat ear, monitored by laser-Doppler flowmetry, with increases in arterial blood pressure and heart rate. These effects were attenuated by previous treatment with reserpine, but reserpine had no effect on the blood flow increase produced by acetylcholine. A dose of propranolol, which caused attenuation of the theophylline-induced increase in heart rate, did not change the peripheral blood flow. The higher dose of propranolol, which nearly canceled the increases in blood pressure and heart rate, caused attenuation of the blood flow increase but did not cancel it. However, the theophylline-induced flow increase was completely reversed by a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, which alone had no effect, without any change in arterial blood pressure and heart rate. Treatment of the rats with the dose of inhibitor slightly and significantly reduced the response of peripheral blood flow to acetylcholine. The other isomer, NG-nitro-D-arginine methyl ester, and the other inhibitor, NG-monomethyl-L-arginine, did not have such an effect. These results suggest that the flow increase is due to an independent effect on the heart with modification by autonomic reflexes and involves the adrenergic and nitrergic pathways.

Role of adenosine in pathogenesis of syndrome X: assessment with coronary hemodynamic measurements and thallium-201 myocardial single-photon emission computed tomography

OBJECTIVES

This study was performed 1) to examine the role of adenosine in the pathogenesis of syndrome X in patients with this syndrome and abnormal results on myocardial scintigrams during exercise, and 2) to determine the susceptibility to myocardial ischemia in this subset of patients with syndrome X.

BACKGROUND

A role for adenosine in the pathogenesis of syndrome X has recently been postulated, but there are few clinical data supporting this hypothesis.

METHODS

Exercise thallium-201 myocardial scintigraphy after intravenous administration of aminophylline, an adenosine receptor blocking agent, or saline solution and adenosine thallium-201 scintigraphy were performed in 26 patients with syndrome X. Hemodynamic variables during exercise and perfusion defect size after aminophylline and saline infusions were compared. At cardiac catheterization, coronary hemodynamic variables during separate infusions of adenosine and doubutamine were also examined and were compared among patients with abnormal or normal scintigrams and 10 control subjects.

RESULTS

Perfusion abnormalities on exercise-thallium-201 scintigraphy occurred in 14 of 26 patients with syndrome X. Intravenous infusion of aminophylline suppressed the scintigraphic perfusion defect and prolonged the time to 1-mm ST segment depression in patients with syndrome X with abnormal exercise scintigrams. Intravenous infusion of adenosine induced a perfusion defect in the same myocardial area where the perfusion defect was observed at exercise in 7 of the 14 patients with syndrome X. At cardiac catheterization, patients with syndrome X with abnormal exercise scintigrams had lower coronary flow reserve and a greater frequency of myocardial lactate production and ST segment depression in response to the infusions of adenosine and doubtamine than did the other two groups. During adenosine infusion, great cardiac vein blood flow and oxygen content were significantly increased and myocardial oxygen consumption and lactate extraction were significantly reduced from baseline without a significant increase in rate-pressure product in this subset of patients with syndrome X.

CONCLUSIONS

Patients with syndrome X with abnormal exercise scintigrams have high susceptibility to myocardial ischemia during exercise or pharmacologic stress tests, probably owing to reduced coronary flow reserve. A heterogeneous response to endogenous adenosine may contribute to scintigraphic perfusion abnormalities and myocardial ischemia during exercise in this subset of patients with syndrome X.

A role for adenosine in coronary vasoregulation in man. Effects of theophylline and enprofylline

Adenosine has been suggested to have a role in regulation of the tone of the cardiac resistance vessels. To elucidate the coronary vasoregulatory role of endogenous adenosine in man, we studied the effects of adenosine receptor antagonism by theophylline on coronary blood flow at rest and during light exercise. However, theophylline may also exert pharmacological effects not related to adenosine antagonism. To clarify the contribution of endogenous adenosine in coronary hyperaemia, the effect of theophylline was compared to that of enprofylline, a xanthine which exerts similar pharmacological effects as theophylline while lacking antagonistic action at adenosine receptors. Twenty healthy subjects (10 males) aged 22-39 years were examined. Coronary sinus (CS) blood flow and blood oxygen content were determined at rest and during supine bicycle exercise, at a load of 50 watts, for 10 min. Thereafter, stepwise infusion of adenosine (30 to 60 micrograms/kg/min into the subclavian vein) was performed. Theophylline or enprofylline treatment was instituted randomly and double-blind (10 in each group), and the procedures (i.e. determinations at rest, during exercise and during infusion of adenosine) were repeated. In all 20 subjects, basal CS flow was 70 +/- 6 ml/min and the cardiac oxygen extraction ((A-CS)O2D) was 123 +/- 3 ml/l. During exercise, CS flow and (A-CS)O2D increased to 135 +/- 17 ml/min and 132 +/- 3 ml/l, respectively. Adenosine increased CS flow dose dependently to 161 +/- 27 ml/min, while (A-CS)O2D decreased to 66 +/- 7 ml/l. The vasodilatory effect of adenosine was readily counteracted by theophylline, the increase in CS flow being 33% vs. 133% in the control situation. Enprofylline, on the other hand, enhanced the response to exogenous adenosine. Theophylline, at a dose lacking effect on heart rate and blood pressure, decreased CS flow at rest by 14% (P < 0.05) and during exercise by 18% (P < 0.05). ((A-CS)O2D increased by 14% at rest and during exercise (P < 0.001). Enprofylline, on the other hand, was without effect. The differences in responses between theophylline and enprofylline with respect to coronary flow and oxygen extraction were significant both at rest and during exercise. It is concluded that theophylline increases coronary vascular resistance, while enprofylline, lacking adenosine antagonistic properties, was without such effect. This indicates a physiological role of adenosine in regulation of coronary flow.

Theophylline increases coronary vascular tone in humans: evidence for a role of endogenous adenosine in flow regulation

To elucidate the role of adenosine in coronary vasoregulation, we studied the effects of adenosine antagonism (by theophylline) on coronary blood flow at different levels of adenosine formation (stimulated by hypoxia and exercise). Six healthy subjects were studied. Coronary sinus (CS) blood flow (thermodilution) and cardiac oxygen extraction [(A-CS)O2D] were determined while breathing room air at rest, and 12% oxygen, both at rest and during light exercise, on two occasions. One of the experiments was performed during infusion of theophylline. The basal CS flow was 118 (67-168) mL min-1 (mean and 95% confidence interval), and the (A-CS)O2D was 125 (111-142) mL L-1. Inhalation of 12% O2 decreased the arterial haemoglobin oxygen saturation to 83 (80-86)% at rest and to 77 (73-81)% during exercise. CS flow increased to 167 (93-214) and 261 (179-343) mL min-1, respectively, and (A-CS)O2D decreased to 102 (85-119) and 94 (77-111) mL L-1, respectively. Theophylline, at a dose lacking effects on myocardial work, markedly attenuated the coronary flow response to exogenous adenosine, and decreased CS flow to 89 (58-119), 120 (79-161) and 190 (162-218) mL min-1 at normoxic rest, hypoxic rest and hypoxic exercise, respectively. The overall decrease amounted to 23% (P < 0.05). The calculated coronary vascular conductance also decreased by 23% (P < 0.05) and (A-CS)O2D increased by 15% (P < 0.001). In conclusion, the data support the hypothesis that endogenous adenosine is involved in regulation of human coronary tone.

Effects of short-term aminophylline administration on cardiac functional reserve in patients with syndrome X

OBJECTIVES

This study sought to evaluate the effect of adenosine receptor blockade by aminophylline on cardiac functional reserve in patients with syndrome X.

BACKGROUND

Aminophylline may have a potentially antiischemic effect through the inhibition of adenosine and, thus, the coronary steal phenomenon in patients with syndrome X.

METHODS

A single-blind, placebo-controlled study of an intravenous infusion of aminophylline (6 mg/kg body weight over 15 min) or placebo (20 ml of saline solution over 15 min) was performed during continuous radionuclide monitoring of left ventricular ejection fraction in 12 patients performing supine bicycle ergometric exercise.

RESULTS

Aminophylline increased exercise time (aminophylline 400 s vs. placebo 355 s, p < 0.01), decreased degree of ST segment depression (aminophylline 1.6 mm vs. placebo 2.4 mm, p < 0.01) and either abolished (seven patients) or diminished (five patients) chest pain during exercise. Aminophylline also increased left ventricular ejection fraction at rest (aminophylline 66.5% vs. placebo 62.3%, p < 0.05) but did not improve its deterioration at peak exercise (aminophylline 60.1% vs. placebo 56.6%, p = NS) or shorten the abnormally prolonged interval between the end of exercise and the overshoot (aminophylline 115 s vs. placebo 130 s, p = NS).

CONCLUSIONS

Aminophylline infusion increases ischemic threshold and prolongs exercise duration in patients with syndrome X. It is hypothesized that aminophylline acts by inhibiting the coronary steal phenomenon through adenosine receptor blockade. It does not improve the deterioration in left ventricular function at peak exercise or the delayed response in ejection fraction in the recovery period, presumably because the beneficial effects of aminophylline that result from the redistribution of coronary blood flow are limited.

Effects of aminophylline on cardiac function and regional myocardial perfusion: implications regarding its antiischemic action

Aminophylline improves exercise capacity in patients with angina. Because this drug does not dilate epicardial coronary vessels, its beneficial effect is from either a reduction of myocardial oxygen consumption or an improvement of myocardial blood flow distribution. This study was performed to assess the effects of aminophylline on cardiac function and on regional myocardial perfusion to establish the mechanisms of its antiischemic action. In 10 patients during cardiac catheterization hemodynamic parameters and cardiac volumes were obtained during baseline and after intravenous infusion of aminophylline. Aminophylline decreased left ventricular end-diastolic pressure (from 11 +/- 4 to 4 +/- 2 mmHg, p < 0.001), mean right atrial pressure (from 5 +/- 2 to 2 +/- 1 mmHg, p < 0.01), and left ventricular end-diastolic volume (from 117 +/- 36 to 88 +/- 36 ml, p < 0.01); it increased peak dp/dt (from 1931 +/- 329 to 2430 +/- 540 mmHg/sec, p < 0.001) and heart rate (from 69 +/- 9 to 76 +/- 14 beats/min, p < 0.05) and did not modify systolic aortic pressure (138 +/- 14 vs 137 +/- 16 mmHg, p = not significant [NS]). Estimated oxygen consumption during aminophylline (6.7 +/- 1.3 ml/min/gm) was similar to that during baseline (6.7 +/- 1.4 ml/min/gm). In another study in nine anesthetized dogs with a critical stenosis of the left anterior descending artery, myocardial perfusion was assessed by microspheres during control atrial pacing and during atrial pacing after aminophylline; left atrial pressure was kept constant throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Bamiphylline improves exercise-induced myocardial ischemia through a novel mechanism of action

BACKGROUND

In patients with stable angina pectoris aminophylline, a nonselective antagonist of adenosine receptors, markedly improves exercise capacity. To establish the role played by A1 adenosine receptors in the anti-ischemic action of aminophylline, the effects of bamiphylline, a selective A1 antagonist, on exercise-induced ischemia were investigated in patients with stable angina pectoris.

METHODS AND RESULTS

In a single-blind, placebo-controlled, randomized cross-over trial in 18 patients, oral administration of 1200 mg bamiphylline increased both the time to 1-mm ST segment depression (from 524 +/- 177 to 664 +/- 192 seconds, P < .01) and the rate-pressure product at 1-mm ST segment depression (from 159 +/- 31 to 190 +/- 34 beats per minute per mm Hg/10(2) (P < .001). End-diastolic and end-systolic left ventricular volumes, left ventricular ejection fraction, and systolic septal and posterior wall thickening investigated by two-dimensional echocardiography in 12 of the 18 patients were not affected by oral administration of bamiphylline (124 +/- 22 versus 125 +/- 20 mL, P = NS; 49 +/- 12 versus 50 +/- 13 mL, P = NS; 60 +/- 8% versus 58 +/- 7%, P = NS; 35 +/- 6% versus 36 +/- 7%, P = NS; 32 +/- 6% versus 33 +/- 6%, P = NS, respectively). In 7 of the 18 patients, the intravenous infusion of bamiphylline (5 mg/kg in 15 minutes) during cardiac catheterization did not produce any significant change of heart rate (76 +/- 10 versus 75 +/- 13 beats per minute, P = NS), mean right atrial pressure (3.8 +/- 1.7 versus 3.7 +/- 1.7 mm Hg, P = NS), mean aortic pressure (102 +/- 12 versus 99 +/- 10 mm Hg, P = NS), or left ventricular end-diastolic pressure (14 +/- 3 versus 14 +/- 4 mm Hg, P = NS) compared with baseline. Furthermore, after intravenous infusion of bamiphylline, the diameter of seven proximal and distal normal segments and of seven stenotic segments were similar to those measured at baseline (3.1 +/- 0.5 versus 3.1 +/- 0.5 mm, P = NS; 1.6 +/- 0.2 versus 1.7 +/- 0.2 mm, P = NS; 1.6 +/- 0.5 versus 1.6 +/- 0.5 mm, P = NS, respectively).

CONCLUSIONS

In patients with stable angina pectoris, oral administration of bamiphylline improves exercise capacity. Its anti-ischemic action does not appear to be mediated by systemic hemodynamic effects or by stenosis dilation. Therefore, the improvement of myocardial ischemia caused by bamiphylline is probably due to redistribution of coronary blood flow toward the underperfused subendocardium. This novel anti-ischemic action would appear to be mediated by antagonism of A1 receptors.

Dose dependency of aminophylline effects on hemodynamic and ventricular function in patients with chronic obstructive pulmonary disease

The effects of aminophylline on pulmonary vascular tone, systemic hemodynamics, and ventricular ejection fractions reported in the literature show some discrepancies. We therefore studied in COPD patients the effects of aminophylline on hemodynamics, on ventricular ejection fractions, and on systolic and diastolic functions of each ventricle, and we measured simultaneously the blood level of the drug. The analysis of the data revealed a relationship between the blood level of aminophylline and the variations of right ventricular ejection fraction (RVEF) (r = 0.83, p = 0.005), left ventricular ejection fraction (LVEF) (r = 0.76, p = 0.017), pulmonary vascular resistance index (PVRI) (r = -0.58, p = 0.096), systemic vascular resistance index (SVRI) (r = -0.60, p = 0.08), and right ventricular peak systolic pressure/end-systolic volume index (RVPSP/ESVI) (r = -0.75, p = 0.02). Modifications of ejection fractions and vascular resistance indices were correlated for both ventricles (RVEF vs PVRI, r = -0.77, p = 0.01; LVEF vs SVRI, r = -0.76, p = 0.02). Finally, RVEF modifications was also correlated to RVPSP/ESVI variation (r = 0.78, p = 0.01). These results suggest that even within the therapeutic range (10 to 20 mg/L), the effects of aminophylline seemed to depend on its blood level. This dose dependency could explain the contradictory data reported in the literature concerning the effects of aminophylline on pulmonary and systemic hemodynamics and on ventricular function.

Effects of intravenous theophylline on exercise-induced myocardial ischemia. I. Impact on the ischemic threshold

OBJECTIVES

Theophylline has been shown to delay the onset of myocardial ischemia and to prolong exercise duration. The present study was done to evaluate the mechanisms and actions of intravenous theophylline on the onset of ischemia and exercise duration.

BACKGROUND

The ischemic threshold may be altered by the differential coronary vasodilation induced by endogenous adenosine. Theophylline is a competitive receptor antagonist of adenosine and may have a potential as an anti-ischemic medication.

METHODS

A double-blind, placebo-controlled crossover trial using an infusion of intravenous theophylline (8.0 +/- 2.0 mg/liter) or placebo before exercise in 12 patients was done. Oxygen uptake, heart rate, blood pressure and heart rate-blood pressure product were determined at the onset of > or = 0.1-mV ST segment depression and angina pectoris, as well as at peak exercise. The extent of myocardial ischemia was evaluated by electrocardiographic criteria and quantitation of thallium-201 images at peak exercise.

RESULTS

When compared with placebo, theophylline significantly delayed time to the onset of exercise-induced ischemia. Ischemia occurred at a higher heart rate-blood pressure product and oxygen uptake. Exercise duration was prolonged but was not associated with greater ischemia, as determined by oxygen uptake, ST segment depression, angina pectoris and size of thallium-201 defect.

CONCLUSIONS

It is concluded that theophylline favorably alters myocardial ischemia not only by delaying its onset but also by enabling it to occur at a higher threshold without causing deleterious effects during exercise. The mechanism for the increased ischemic threshold may be through the inhibition of adenosine and the coronary steal phenomenon.

Microvascular sites and mechanisms responsible for reactive hyperemia in the coronary circulation of the beating canine heart

Our aim was to elucidate the site and mechanism responsible for reactive hyperemia in coronary circulation. In in vivo beating canine hearts, microvessels of the left anterior descending coronary artery (LAD) were observed through a microscope equipped with a floating objective. Flow velocity of the LAD was measured with a suction-type Doppler probe. The LAD was occluded for 20 or 30 seconds and then released, and reactive hyperemia was observed before and after 8-phenyltheophylline (7.5 mg/kg i.v.) or glibenclamide (200 micrograms/kg into the LAD) infusion. During the occlusion, only arterial microvessels smaller than 100 microns in diameter dilated. Dilation of those vessels was partially attenuated by 8-phenyltheophylline and completely abolished with glibenclamide. In the early phase of reactive hyperemia, all arterial microvessels dilated, and the magnitude of peak dilation was greater in vessels smaller than 100 microns compared with those larger than 100 microns. Vasodilation during reactive hyperemia ceased within 60 seconds in vessels smaller than 100 microns but was sustained for more than 120 seconds in those larger than 100 microns. 8-Phenyltheophylline did not change peak dilation of arterial microvessels but reduced dilation after the peak. Glibenclamide remarkably attenuated dilation of all arterial microvessels in the whole phase of reactive hyperemia. These results indicate that all arterial microvessels are responsible for reactive hyperemia after coronary artery occlusions of 20-30 seconds, but there is greater participation of vessels smaller than 100 microns in the early phase of reactive hyperemia. Dilation of vessels larger than 100 microns assumes an important role in the later phase. ATP-sensitive K+ channels mediate dilation of arterial microvessels both in brief ischemia and reactive hyperemia.

Improved working capacity in patients with ischaemic heart disease during a 10-day treatment with oral theophylline

The objective of this study was to assess whether a 10-d treatment with oral theophylline improves the working capacity in patients with ischaemic heart disease, and to compare theophylline with conventional anti-anginal therapy. Twenty-four patients with stable effort-induced angina were included in the study. The patients received double-blind treatment in randomized order during 4 consecutive 10-d periods, separated by a 4-d wash-out period, with (a) metoprolol durules 200 mg once daily + theophylline durules 300 mg b.i.d., (b) theophylline + placebo, (c) metoprolol + placebo, and (d) placebo alone. At the end of each period a supine exercise stress test was performed. Maximal workload increased to 111 +/- 6 W during treatment with theophylline, compared to 106 +/- 6 W during placebo treatment (P = 0.01). Metoprolol increased the maximal workload to 117 +/- 6 W (P less than 0.001). The effects of metoprolol and theophylline were additive, and the working capacity increased to 123 +/- 7 W during combined therapy. Neither the degree of ST-depression nor the scoring of chest pain at maximal workload differed between the four treatment regimens. An improved working capacity was shown in patients with stable effort-induced angina pectoris during long-term theophylline treatment. The effect was additive to that of beta-blockade.

Increase in ocular blood flow induced by isobutylmethylxanthine and epinephrine

Alterations in regional blood flow of the eye were studied in rabbits using the radioactively labelled microsphere technique. The animals were topically treated with 1% IBMX, 0.1% epinephrine in combination with 1% isobutylmethyl-xanthine (IBMX), or with 0.1% epinephrine alone. After IBMX there was a tendency towards an increase in blood flow in the iris, ciliary processes and sclera, whereas the choroidal blood flow tended to decrease. After epinephrine the iridial blood flow increased about 50% at 6 hr. After IBMX combined with epinephrine a biphasic response was obtained: an initial decrease in blood flow of the iris, the ciliary processes and to some extent the choroid was followed by a marked and long lasting increase in blood flow from 2.5 to 7.5 hr in the iris (up to 220%), ciliary processes (123%) and sclera (115%). The choroidal blood flow was not increased. The marked increase in blood flow of the iris and the ciliary processes indicates that the reduction of intraocular pressure seen after topical treatment with a combination of epinephrine and IBMX, is not based on a vascular mechanism. The increase of ocular blood flow after a combination of IBMX and epinephrine is probably based on increased cAMP secondary to inhibition of phosphodiesterases. This may indicate the presence of beta-adrenergic receptors in the ocular vasculature.

Effects of theophylline, atenolol and their combination on myocardial ischemia in stable angina pectoris

The effects of theophylline (400 mg twice a day), atenolol (50 mg twice a day) and their combination on myocardial ischemia were studied in 9 patients with stable angina pectoris in a randomized, single-blind, triple crossover trial. Placebo was administered to the patients during the run-in and the run-off periods. A treadmill exercise test and 24-hour ambulatory electrocardiographic monitoring were obtained at the end of each treatment period. Compared with placebo, theophylline significantly improved the time to onset of myocardial ischemia (1 mm of ST-segment depression) from 7.8 +/- 3.7 to 9.5 +/- 3.7 minutes (p less than 0.03) and the exercise duration from 9 +/- 3.4 to 10.1 +/- 3.5 minutes (p less than 0.04). During atenolol and during combination treatment, the time to the onset of ischemia and the exercise duration were similar (10.8 +/- 4.2 and 11.2 +/- 3.2 minutes, 11.2 +/- 3.6 and 11.5 +/- 3.2 minutes, respectively) and longer than during theophylline administration (p less than 0.05). Ambulatory electrocardiographic monitoring showed that, during theophylline administration, the heart rate was higher than during placebo throughout the 24 hours (p less than 0.05). During atenolol and during combination treatment the heart rate was similar and in both cases lower than during placebo (p less than 0.05). Compared with placebo, theophylline decreased the total ischemic time from 97 +/- 110 to 70 +/- 103 minutes (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine is not essential for exercise hyperaemia in the hindlimb in conscious dogs

1. The contribution of endogenous adenosine to the increase in hindlimb blood flow that occurs during treadmill exercise was evaluated in conscious dogs. We postulated that if adenosine is essential for the hindlimb hyperaemic response, then pharmacological treatment of the animals with adenosine receptor antagonists should decrease hindlimb blood flow during treadmill exercise. 2. A total of twenty-three dogs were chronically instrumented for measurement of aortic blood pressure and hindlimb blood flow using electromagnetic or Doppler flow probes on the left external iliac artery. Measurements of arterial blood pressure, hindlimb blood flow and heart rate were made during steady-state treadmill exercise in both the presence and the absence of adenosine receptor antagonists. Four different protocols were performed using different routes of administration of two adenosine receptor antagonists. Aminophylline was used in most of the experiments, and the effects of the more potent antagonist, 8-phenyltheophylline, were also evaluated. In addition, the dogs exercised at varying intensities ranging from a low level of 5.5 km h-1 at 0% gradient to a high intensity of 5.5 km h-1 at 21% gradient. 3. Aminophylline given as a single intravenous dose, or as a constant infusion either intravenously or directly into the hindlimb artery, did not decrease hindlimb blood flow at low, moderate or high intensities of exercise. Likewise, the blockade of adenosine receptors with 8-phenyltheophylline, given systemically or as a bolus injection administered directly into the hindlimb circulation during moderate exercise, did not attenuate the hindlimb blood flow response. 4. Our data demonstrate that exercise hyperaemia of the hindlimb is not reduced by antagonism of adenosine receptors. These findings are consistent with the hypothesis that adenosine is not an essential mediator of hindlimb vasodilatation during exercise.

Cardiovascular-pulmonary interaction in chronic obstructive pulmonary disease with special reference to the pathogenesis and management of cor pulmonale

Chronic obstructive pulmonary disease (COPD), which here refers to a group of diseases that have in common the physiologic defect of airway obstruction, is often associated with severe hemodynamic consequences. This article provides an overview of cardiovascular function in COPD with emphasis on recent advances in detecting, quantifying, and treating pulmonary hypertension and its major cardiac complication, cor pulmonale.

Comparative effects of theophylline and isosorbide dinitrate on exercise capacity in stable angina pectoris, and their mechanisms of action

While the role of nitrates in the prevention and treatment of myocardial ischemia is well established, the use of theophylline, proposed almost a century ago, is still controversial. Also controversial is its mechanism of action, initially thought to be coronary dilation. In this randomized, single-blind study, the acute effects on exercise capacity of sublingual isosorbide dinitrate (10 mg) and of intravenous theophylline ethylenediamine (7 mg/kg) were assessed in 10 patients with chronic stable angina and positive exercise test. After the administration of theophylline, the time to onset of angina, the heart rate-blood pressure product at 1-mm ST-segment depression and the exercise duration were similar to that after isosorbide dinitrate administration (9.8 +/- 2.3 vs 9.3 +/- 1.7 minutes, 207 +/- 41 vs 207 +/- 48 beats/min.mm Hg.10(-2) and 10.8 +/- 2 vs 10.4 +/- 2 minutes, respectively). Both drugs significantly (p less than 0.001) improved all these parameters compared to the baseline exercise test. The effect of the 2 drugs on the diameters of angiographically normal segments of large epicardial coronary arteries was then assessed using computerized quantitative angiography in 10 other patients with stable angina. Whereas theophylline failed to increase the coronary diameters compared to that in the baseline angiogram (2.9 +/- 0.6 vs 2.9 +/- 0.6 mm, respectively), the subsequent administration of isosorbide dinitrate resulted in an increase up to 3.2 +/- 0.7 mm (p less than 0.02). Thus, in patients with stable angina, theophylline delays the onset of angina, increases the ischemic threshold and prolongs the exercise duration to the same degree as isosorbide dinitrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of myocardial oxygen consumption in dipyridamole-induced ischemia

The aim of this study was to assess whether myocardial oxygen consumption can be responsible for aminophylline resistance in dipyridamole-induced ischemia. We analyzed 163 consecutive patients who had a positive low-dose (0.56 mg/kg over 4 minutes) dipyridamole-echocardiography test, requiring intravenous aminophylline as an antidote. All patients also performed an exercise stress test. In 141 of these patients, the signs of ischemia were reversed by administration of intravenous aminophylline (group I), while the remaining 22 patients were resistant to aminophylline (240 mg/kg over 3 minutes) and received additional treatment with nitrates to relieve ischemia (group II). The increase in rate-pressure product (RPP = mm Hg x beats/min x 100) measured during the exercise stress test in the patients in group I was significantly greater than that determined during dipyridamole-induced ischemia (204 +/- 41 versus 145 +/- 33, p less than 0.01). However, the increases in RPP under both conditions were similar for the patients in group II (147 +/- 24 versus 150 +/- 20, p = ns). In patients with dipyridamole-induced ischemia who were resistant to aminophylline, the rise in myocardial oxygen consumption--probably linked to reflex sympathetic activation--might maintain ischemia independently from flow maldistribution, which should be reversed by aminophylline.

Effect of theophylline on exercise-induced myocardial ischaemia

In a single-blind, placebo-controlled, randomised trial in 20 patients with stable angina pectoris, intravenous theophylline ethylenediamine (aminophylline), 7 mg/kg, increased the time to onset of angina by 46%, the heart-rate/blood-pressure product (an index of myocardial oxygen consumption) at 1 mm ST segment depression by 22%, and exercise duration by 24%. In a subsequent double-blind placebo-controlled trial in 8 patients a single oral dose of theophylline (375 mg) increased the time to onset of angina by 56%, the heart-rate/blood-pressure product at 1 mm ST segment depression by 22%, and the exercise duration by 35%. Infusion of theophylline ethylenediamine during angiography (10 patients) did not affect the diameter of epicardial coronary arteries. The beneficial effects of theophylline may be due to redistribution of coronary blood flow from non-ischaemic to ischaemic myocardium.

Exercise capacity after acute aminophylline administration in angina pectoris

Exercise-induced ischemia is generally attributed to an increase in myocardial demand in the presence of coronary stenosis limiting flow supply. An additional mechanism--the occurrence of coronary steal due to excessive endogenous adenosine release--has also been hypothesized. The effect of adenosine receptor blocking by aminophylline in effort ischemia was tested in 8 patients with stable effort-induced angina pectoris, reproducible positive exercise stress tests and angiographically assessed coronary artery disease. Following double-blind, randomized intravenous infusion of aminophylline (3 mg/kg over 3 minutes) or placebo (20 ml of saline over 3 minutes), the patients underwent upright bicycle exercise stress tests on 2 consecutive days. After aminophylline, there was an increase in work tolerance (aminophylline 7.5 +/- 1.8 minutes of exercise vs placebo 5.4 +/- 1.5 minutes; p less than 0.05). There was a parallel increase in the ischemic threshold, evaluated with the rate-pressure product (mm Hg X beats/min X 100(-2)) at 0.1 mV of ST-segment depression (221 +/- 35 vs 184 +/- 20; p less than 0.01). Thus, at a dosage that should effectively inhibit adenosine receptors, aminophylline infusion exerts a beneficial effect on exercise-induced ischemia, possibly through the prevention of myocardial flow maldistribution elicited by excessive adenosine release during effort.

Improved working capacity following theophylline infusion in patients with ischaemic heart disease

The effect of theophylline on the working capacity of patients with ischaemic heart disease was evaluated in a double-blind, randomized cross-over study. Eight patients, receiving no medication, with stable effort-provoked angina pectoris and typical exercise-induced ST depressions were studied. Following intravenous administration of theophylline or placebo, the patients did a supine leg exercise limited by intolerable chest pain. The workload was continuously increased by 10 W/min. Following theophylline treatment the workload at the onset of chest pain increased from 71 +/- 9 to 114 +/- 14 W (P less than 0.002). The ST depression was less pronounced following theophylline at submaximal exercise (-0.01 +/- 0.00 vs. -0.09 +/- 0.02 mV, P less than 0.005, at 70 W). The maximum tolerable workload increased from 129 +/- 15 after placebo infusion to 153 +/- 12 W after theophylline infusion P less than 0.01). It is speculated that this beneficial effect of the adenosine receptor antagonist theophylline may possibly be due to inhibition of a pathophysiological coronary steal induced by elevated levels of adenosine during ischaemia.

Pharmacodynamics and pharmacokinetics of enprofylline and theophylline in the isolated rabbit heart

The direct effects of theophylline and enprofylline, a new anti-asthma xanthine derivative without adenosine receptor blocking action, were studied in the isolated, spontaneously beating rabbit heart. At increasing concentrations from 2 x 10(-5)-5 x 10(-4) M both drugs produced increases in heart rate up to 143% and 162% and in contractility up to 135% and 147% from control values (100%), respectively. At concentrations higher than 10(-3) M contractures and heart block occured. Enprofylline showed a potency about 2.3 times higher than theophylline. Coronary flowrate did not increase. Myocardial oxygen consumption was moderately increased by the drugs. The myocardial pharmacokinetics showed two-compartment characteristics for both drugs. Half-times of the two phases of accumulation were for theophylline 0.28 and 0.98 min. and for enprofylline 0.31 and 0.78 min. The terminal disposition half-time for enprofylline was, however, 2.7 times higher than that of 0.91 min. for theophylline, apparently due to a stronger binding of the former drug intracellularly. Both xanthines accumulated against a concentration gradient showing myocardial tissue-perfusion liquid ratios of about 2.9 for theophylline and 3.7 for enprofylline. The drugs seem to exert their primary action on sarcolemmal binding sites which probably are unrelated to adenosine receptors.

Aminophylline has little positive inotropic effect and a slightly negative diastolic effect on the left ventricle during hypoxic conditions in dogs

We examined the effect of aminophylline on left ventricular (LV) mechanics and central hemodynamics under normoxic and hypoxic conditions in respective groups of dogs. In an open-chest preparation, LV end-systolic and diastolic dimensions were measured with ultrasonic crystal transducers seated subendocardially along the anterior to posterior and apex to base axes. In the group studied during hypoxia, measurements were obtained during 3 conditions: normoxia; hypoxia to a PO2 of 30 mm Hg; and during hypoxia when aminophylline was infused to a blood level of about 15 mg/L. In the group studied under normoxic conditions, measurements were initially obtained during normoxia after which aminophylline was also infused to a blood level of 15 mg/L. Intravascular volume was given or removed to maintain LV filling pressures at about 10 mm Hg during all conditions. In the normoxic group, aminophylline caused an increase in stroke volume (SV) and had a positive inotropic effect on the LV. End-systolic dimensions were reduced, while end-diastolic dimensions did not change with aminophylline. On the other hand, under hypoxic conditions, aminophylline did not have a positive inotropic effect: SV did not increase and end-systolic dimensions remained unchanged. Under hypoxic conditions, moreover, aminophylline caused a slight decrease in end-diastolic dimensions by augmenting hypoxia-induced increases in myocardial resting tension. Our results indicate that unlike normoxic conditions, aminophylline may have little beneficial effect on LV performance during hypoxic conditions.

Cardiac output changes secondary to theophylline therapy in preterm infants

The cardiovascular effects of theophylline were studied in 11 clinically stable preterm infants. Theophylline was given as aminophylline using a loading dose of 6.8 mg/kg and a maintenance dose of 2 mg/kg every 8 hours intravenously. Cardiac output, stroke volume, and heart rate were measured using a combination of pulsed Doppler ultrasound and M-mode echocardiography. Compared with day 0, an increase was found in both cardiac output (P less than 0.01) and stroke volume (P less than 0.02) on days 1, 2, and 3. By day 7, stroke volume was comparable to pretreatment values, whereas cardiac output was still increased. Heart rate was augmented significantly (P less than 0.01) throughout the treatment period. Mean arterial blood pressure did not change. All but one of the neonates had serum theophylline concentrations between 6 and 13 mg/L. We conclude that both inotropic and chronotropic effects are evident during the first days of theophylline therapy. The metabolic cost of the increased cardiac output in the preterm infant with theophylline therapy deserves further attention.

Theophylline poisoning. Pharmacological considerations and clinical management

The recent marketing of slow release preparations of theophylline and new indications for the use of the drug have resulted in a marked increase in the sale of theophylline products. This phenomenon combined with the drug's highly variable pharmacokinetics has led to an increase in the number of theophylline intoxications. The morbidity and mortality rates associated with theophylline intoxication are significant. Therefore it is essential that clinicians are aware of the pathophysiology, clinical presentation and treatment of this poisoning. Theophylline intoxication mainly affects the gastrointestinal, cardiovascular and central nervous systems. Signs and symptoms range from mild gastrointestinal upset to serious central nervous system manifestations such as seizures, a symptom often associated with a bad prognosis. Theophylline serum concentrations are very useful for making decisions regarding treatment. However, their interpretation should take into account several factors such as the age of the patient and the type of intoxication (acute versus chronic). Prevention of gastrointestinal absorption should be the principal objective of treatment of an oral theophylline poisoning. The repetitive administration of activated charcoal not only prevents theophylline absorption but also increases its rate of Once absorbed, external methods such as haemodialysis and haemoperfusion can significantly accelerate the elimination of the drug from the body. Finally, the rapid suppression of seizures and cardiac arrhythmias are essential to prevent severe neurological sequelae and death. Since theophylline intoxication can be potentially life-threatening, its administration should be monitored with regular measurements of the serum theophylline concentration, especially in the very young and the very old.

Some dynamic and toxic effects of theophylline in horses

A single intravenous administration of theophylline as aminophylline at 10 mg/kg to four mares induced a diuresis in which maximal urine production was more than seven times the control volume. The diuretic effect was maximal within the first hour post-administration, and lasted approximately 6 h. Theophylline resulted in dose-related tachycardia, polypnoea and nervous symptoms (tactile, visual and auditory hypersensitivity, muscle tremor, sweating) in normal mares, but had only minor effects on arterial and central venous blood pressures, intrapleural pressure, red blood cell variables and plasma proteins. The upper limit of safe plasma theophylline concentration in horses is approximately 15 micrograms/ml. Whenever feasible, the oral or intragastric route of administration should be used as it is safer than the intravenous route.

Cardiovascular effects of two different xanthines in healthy subjects. Studies at rest, during exercise and in combination with a beta-agonist, terbutaline

The haemodynamic response to two xanthines, enprofylline and theophylline, was studied in 6 healthy male volunteers at rest, during exercise and in combination with the beta 2-agonist, terbutaline. At rest the haemodynamic effects of both xanthines were small and were qualitatively different from each other. While theophylline exerted a "pressor" response, enprofylline seemed to have arterial dilating ability. During exercise both xanthines as compared to placebo were associated with a higher heart rate and in general with increased systolic blood pressure. In combination with terbutaline enprofylline and theophylline both increased systolic blood pressure more than placebo, i.e. they augmented the positive inotropic effect of terbutaline. The systolic blood pressure was higher after theophylline than enprofylline despite their equipotent bronchodilator activity. This may reflect different inotropic effects of the xanthines as well as a difference in their influence on the response to adenosine.

Dipyridamole dilates large coronary arteries in conscious dogs

The effects of 0.25 mg/kg dipyridamole on left ventricular (LV) pressures, LV dP/dt, heart rate, aortic pressures, left circumflex coronary blood flow, and left circumflex coronary arterial diameters and on calculations of late diastolic coronary resistance and large coronary cross-sectional area were studied in 15 conscious dogs. Injection of dipyridamole, a drug that has a mechanism of action dependent on myocardial adenosine production, caused sustained increases in mean coronary blood flow (244 +/- 28%), large coronary arterial cross-sectional area (28 +/- 3.2%), heart rate (32 +/- 3.6%), and LV dP/dt (23 +/- 3.0%) and reductions in late diastolic coronary resistance (73 +/- 2.4%) and mean arterial pressure (14 +/- 1.9%). Neither beta-adrenergic-receptor blockade alone nor in conjunction with constant heart rate affected the dilation of large coronary arteries to dipyridamole significantly. Ganglionic blockade with hexamethonium also had little effect on the response of large and small coronary vessels to dipyridamole. Surprisingly neither beta-adrenergic-receptor nor ganglionic blockade abolished the rise in LV dP/dt observed after dipyridamole. Aminophylline, however, effectively eliminated the dilation of large coronary arteries and resistance coronary vessels in response to dipyridamole. In summary, as long as dipyridamole does not induce severe sustained hypotension it exerts potent effects on both coronary arterial resistance and large coronary arteries in the conscious dog. The coronary dilation is independent of reflex adrenergic activation, but appears dependent on myocardial adenosine production.