Impact of beta-blockers on cardiopulmonary exercise testing in patients with advanced liver disease

BACKGROUND

Patients with advanced liver disease may develop portal hypertension that can result in variceal haemorrhage. Beta-blockers reduce portal pressure and minimise haemorrhage risk. These medications may attenuate measures of cardiopulmonary performance, such as the ventilatory threshold and peak oxygen uptake measured via cardiopulmonary exercise testing.

AIM

To determine the effect of beta-blockers on cardiopulmonary exercise testing variables in patients with advanced liver disease.

METHODS

This was a cross-sectional analysis of 72 participants who completed a cardiopulmonary exercise test before liver transplantation. All participants remained on their usual beta-blocker dose and timing prior to the test. Variables measured during cardiopulmonary exercise testing included the ventilatory threshold, peak oxygen uptake, heart rate, oxygen pulse, the oxygen uptake efficiency slope and the ventilatory equivalents for carbon dioxide slope.

RESULTS

Participants taking beta-blockers (n = 28) had a lower ventilatory threshold (P <.01) and peak oxygen uptake (P = .02), compared to participants not taking beta-blockers. After adjusting for age, the model of end-stage liver-disease score, liver-disease aetiology, presence of refractory ascites and ventilatory threshold remained significantly lower in the beta-blocker group (P = .04). The oxygen uptake efficiency slope was not impacted by beta-blocker use.

CONCLUSIONS

Ventilatory threshold is reduced in patients with advanced liver disease taking beta-blockers compared to those not taking the medication. This may incorrectly risk stratify patients on beta-blockers and has implications for patient management before and after liver transplantation. The oxygen uptake efficiency slope was not influenced by beta-blockers and may therefore be a better measure of cardiopulmonary performance in this patient population.

A Comparison of Bone Mineral Density in Amateur Male Boxers and Active Non-boxers

To examine the site-specific osteogenic effect of upper limb impact-loading activity we compared the forearm and arm bone mineral density (BMD) of male boxers to that of active controls. A cross-sectional study was performed with 30 amateur male boxers (aged 18-44 years) and 32 age-matched, non-boxing, active controls. Participants had their regional and whole body BMD and bone mineral content (BMC) assessed by dual-energy X-ray absorptiometry. Hand grip strength, testosterone, oestradiol, sex hormone-binding globulin, vitamin D, lean and fat mass, and past and current physical activity were also assessed. Forearm and arm BMD were 1.5-2.2% higher in boxers than the control group although this was not statistically significant (p>0.05), with no significant difference for BMC (p>0.05). There were no differences between groups for spine, hip, or whole body BMD or BMC, or for body composition or hormone status. Within the arms, lean mass was associated with BMD and BMC in both boxers and the control group (BMD, r=0.60-0.76, p<0.001; BMC, r=0.67-0.82, p<0.001). There were no significant differences between amateur boxers and the control group for upper limb BMD and BMC. However, muscle mass appears to be particularly important to bone health of the upper limbs.

The relationship between BPAQ-derived physical activity and bone density of middle-aged and older men

The bone-specific physical activity questionnaire (BPAQ) accounts for activities that affect bone but has not been used in studies with older adults. Relationships exist between the BPAQ-derived physical activity and bone density in healthy middle-aged and older men but not men with prostate cancer. Disease-related treatments detrimental to bone should be considered when administering the BPAQ.

INTRODUCTION

The bone-specific physical activity questionnaire (BPAQ) was developed to account for bone-specific loading. In this retrospective study, we examined the relationship between BPAQ-derived physical activity and bone mineral density (BMD) in middle-aged and older men with and without prostate cancer.

METHODS

Two groups, 36 healthy men and 69 men with prostate cancer receiving androgen suppression therapy (AST), completed the BPAQ and had whole body, total hip, femoral (FN) and lumbar spine BMD assessed by dual-energy X-ray absorptiometry.

RESULTS

Past (pBPAQ), current (cBPAQ) and total BPAQ (tBPAQ) scores for the healthy men were related to FN BMD (pBPAQ r = 0.36, p = 0.030; cBPAQ r s = 0.35, p = 0.034; tBPAQ r = 0.41, p = 0.014), and pBPAQ and tBPAQ were related to total hip (r s = 0.35, p = 0.035 and r s = 0.36, p = 0.029, respectively) and whole body BMD (r s = 0.44, p = 0.007 and r s = 0.45, p = 0.006, respectively). In men with prostate cancer, the BPAQ was not significantly associated with BMD. In stepwise regression analyses, body mass and tBPAQ predicted 30 % of the variance in total hip BMD (p = 0.003), cBPAQ predicted 14 % of the variance in FN BMD (p = 0.002), and body mass, age and tBPAQ predicted 47% of the variance in whole body BMD (p < 0.001) in healthy men. In men with prostate cancer, the BPAQ was not an independent predictor of BMD.

CONCLUSIONS

Although BPAQ-derived estimates of physical activity are related to bone status in healthy middle-aged and older men, the adverse effect of AST on bone appears to obscure this relationship in men with prostate cancer.

Short-term oral 3-hydroxypyridin-4-one dosing increases aluminum excretion and partially reverses aluminum-induced toxicity in the rabbit independent of chelator lipophilicity

The objectives of the present study were to determine the efficacy and toxicity of repeated oral administration of 3-hydroxypyridin-4-one (HP) chelators in a rabbit model of aluminum (Al) accumulation and toxicity, and the influence of chelator lipophilicity on these effects. Efficacy was assessed as chelator-induced Al mobilization and excretion and reversal of Al accumulation and Al-induced toxicity. Chelator-induced toxicity was assessed by multiple measures. Six HPs were given orally 12 times over 1 month to Al-loaded rabbits, which had significant elevation of Al in most tissues and evidence of Al-induced nephrotoxicity, osteomalacia, and anemia. Intravenous desferrioxamine (DFO), the current chelator of choice for the treatment of Al-overload and toxicity, was included as a positive control. All six HPs and DFO demonstrated efficacy evidenced by significantly greater urinary and biliary Al elimination after the twelfth dose than seen in saline-treated controls. All of the HPs were more effective than DFO. Chelator-induced urinary Al excretion accounted for 58-98% of total (urinary plus biliary) Al excretion. Chelator-facilitated Al excretion was nearly complete within 12 hr, demonstrating a fairly short duration of action in rabbits with intact renal function. HP treatments did not consistently affect tissue concentrations of Al or other metals. However, there was a trend toward chelator-induced reduction of Al-induced nephrotoxicity. The influence of HP lipophilicity was limited to a positive correlation between HP x Al lipophilicity and biliary Al output and a negative correlation between HP and HP x Al lipophilicity and reduction of Kupffer cell Al. Little toxicity was evident after repeated oral HP dosing. Adrenal weight increased after treatment with several HPs. There was a decrease in testes weight after several HPs, which is consistent with an antiproliferative effect. More frequent dosing and/or a longer duration of HP treatment might produce greater reversal of the Al-induced toxicity and perhaps reveal more adverse effects than seen in this study. There was a lack of profound toxicity during this short-term study. The 1,2-dimethyl (CP20) and 1,2-diethyl (CP94) HPs, which have been the most extensively studied HPs, were the least effective of the HPs examined. These results encourage the further investigation of other HPs as oral alternatives to DFO for the treatment of Al accumulation and toxicity.

Oxidative metabolism of 1-(2-chloroethyl)-3-alkyl-3- (methylcarbamoyl)triazenes: formation of chloroacetaldehyde and relevance to biological activity

(Methylcarbamoyl)triazenes have been shown to be effective cancer chemotherapeutic agents in a number of biological systems. Because of their chemical stability, it is likely that their activity in vivo is the result of a metabolic activation process. Previous studies have shown that 1-(2-chloroethyl)-3-methyl-3-(methylcarbamoyl)triazene (CMM) and 1-(2-chloroethyl)-3-benzyl-3-(methylcarbamoyl)triazene (CBzM) are metabolized by rat liver microsomes in the presence of NADPH to yield the ((hydroxymethyl)carbamoyl)triazene analogs of the parent compounds. The present studies show that both compounds are also oxidized at the chloroethyl substituent to yield chloroacetaldehyde and a substituted urea. In the case of CBzM metabolism, 47% of the metabolized parent compound was recovered as benzylmethylurea, 8% was recovered as benzylurea, and 26% was recovered as the ((hydroxymethyl)carbamoyl)-triazene and carbamoyltriazene metabolites. These results suggest that the chloroethyl group is the favored initial site of metabolism. In reaction mixtures containing initial concentrations of 300 microM CBzM, 78 microM chloroacetaldehyde was produced, as compared to 58 microM chloroacetaldehyde produced from the metabolism of 300 microM CMM. The formation of chloroacetaldehyde, a known mutagenic DNA alkylating agent, may explain the biological activity of these compounds.

The 3-hydroxypyridin-4-ones more effectively chelate aluminum in a rabbit model of aluminum intoxication than does desferrioxamine

This study was conducted to assess the influence of lipophilicity on the in vivo aluminum (Al) chelation activity of 3-hydroxypyridin-4-ones (HPs). Chelation activity was evidenced as increased Al elimination in an animal model of Al accumulation and toxicity. The subjects were Al-loaded rabbits. A non-Al-loaded group was included to characterize the rabbit model of Al intoxication. Eight HPs and desferrioxamine (DFO), the drug currently used to treat Al intoxication, were studied. Chelation activity was determined from quantitative biliary and urinary Al excretion and serum Al determinations conducted for 24 hr after DFO or HP intravenous administration, compared with saline. Toxicity was evaluated by observation, blood biochemistry assays, hematological evaluation, gross necropsy, and histopathological assessment of the liver. Al loading produced nephrotoxicity, hepatotoxicity, and anemia. Each of the chelators mobilized Al into serum. The efficiency of Al chelation, calculated from 24-hr biliary plus urinary Al output, ranged from 2.8 to 11.7% for the HPs, compared with 2.1% for DFO. Urinary Al excretion accounted for 78-98% of total Al excretion. Nearly all of the chelator-facilitated Al excretion occurred within 8 hr of dosing. Al chelation efficacy did not correlate with HP or HP Al lipophilicity; however, increasing HP lipophilicity increased the biliary fraction of the excreted Al. There was no evidence for toxicity after HP dosing, other than the previously shown ability of one of the HPs to produce seizures. The greater chelation efficacy of the HPs than DFO provides advantages over DFO. The lack of toxicity after a single dose of all but the most lipophilic HP encourages their further evaluation as orally effective chelators.

HPLC quantitation of a very hydrophilic 3-hydroxypyridin-4-one chelator using a simple separation procedure and the baseline file subtraction method

The lack of a method to isolate very hydrophilic 3-hydroxypyridin-4-ones (HPs) from blood has prevented determination of their pharmacokinetics. The objective of this study is to develop method to quantitate these compounds. A simple sample preparation method coupled with high-performance liquid chromatography is used to quantitate 1-[ethan-1-ol]-2-methyl-3- hydroxypyridin-4-one, a very hydrophilic HP, in plasma. Plasma proteins are precipitated by trichloroacetic acid. The baseline file subtraction method is used to improve the resolution of this HP in the presence of interfering chromatographic peaks that could not be resolved from the HP by the methods investigated. The method is used to determine the pharmacokinetics of this HP in rabbits. The precision of the pharmacokinetic results is comparable or better than the results obtained from seven more lipophilic HPs that were separated by a published method. The new method is slightly modified and used in a study of the pharmacokinetics of this HP in the rat, and precision is comparable with results obtained with two more lipophilic HPs determined by the published method. Baseline file subtraction is useful when other methods cannot be used to adequately resolve a hydrophilic analyte from coeluting interfering substances.

Three different calmodulin-encoding cDNAs isolated by a modified 5'-RACE using degenerate oligodeoxyribonucleotides

In order to obtain the 5' ends of the three mouse calmodulin (CaM) cDNAs, we modified the standard 5' RACE (rapid amplification of cDNA ends) method to use degenerate synthetic oligodeoxyribonucleotides to prime cDNA synthesis of all three CaM mRNAs. In this modified method, the degenerate primers were annealed to mRNAs in an incubation step prior to the reverse transcription reaction. Separating the annealing step from the reverse transcription reaction allowed for greater stringency by using higher temperatures than could be tolerated if the reverse transcriptase were present. Annealing was also done with lower primer concentration and was driven by a longer incubation time. After the annealing step, cDNA synthesis was initiated by diluting the annealing mixture into a 42 degrees C buffer with reverse transcriptase. The synthesized cDNA was poly(dA)-tailed to allow PCR amplification of the first-strand cDNA with an anchor-dT17 primer and the degenerate primers. The CaM cDNAs were evident after this PCR. A second PCR, with nested gene-specific primers, was used to isolate the individual CaM cDNAs from the products of the first PCR. Three distinct CaM cDNAs were cloned and sequenced. By comparison of the 5' untranslated sequences between the mouse CaM DNAs and rat CaM cDNAs, the corresponding homologs were assigned. The results suggest that application of this modified RACE method could improve the success of isolating specific cDNAs in cases where use of a nested primer is not possible or when amino-acid sequence information is available and only degenerate primers can be designed for cloning cDNAs by the 5'-RACE method.

An unexpected pathway for the metabolic degradation of 1,3-dialkyl-3-acyltriazenes

In the presence of NADPH, rat liver microsomes catalyzed the degradation of a series of 1,3-dialkyl-3-acyltriazenes, and the extent of the reaction was correlated with compound lipophilicity. In the case of two methylcarbamoyltriazenes, 1-(2-chloroethyl)-3-benzyl-3- (methylcarbamoyl)triazene (CBzM) and 1-(2-chloroethyl)-3-methyl-3-(methylcarbamoyl)triazene (CMM), microsomal metabolites were isolated. Identification of the CBzM metabolites as 1-(2-chloroethyl)-3-benzyl-3-(hydroxymethylcarbamoyl)triazene and 1-(2-chloroethyl-3-benzyl-3-carbamoyltriazine, and the CMM metabolite as 1-(2-chloroethyl)-3-methyl-3-(hydroxymethylcarbamoyl)triazene indicated that the first metabolic step involves hydroxylation of the methylcarbamoyl substituent. Detailed studies of the metabolism of CBzM indicated that the Km for the reaction was 84 microM, and that metabolism was more efficient if microsomes were prepared from male than from female rats. During prolonged incubation, the metabolites of CBzM were also degraded. The degradation of CBzM and its metabolites was inhibited by SKF-525A and metyrapone, suggesting the involvement of a cytochrome P450 isozyme, and supporting the hypothesis that the process is oxidative rather than hydrolytic in both cases. Metabolic oxidation represents an alternative pathway to chemical or enzymatic hydrolysis for the in vivo decomposition of (methylcarbamoyl)triazenes. This mechanism may ultimately explain the antitumor efficacy and low acute toxicity of selected compounds.

Pharmacokinetics of representative 3-hydroxypyridin-4-ones in rabbits: CP20 and CP94

Selected 3-hydroxypyridin-4-ones (HPs) are under clinical investigation as iron chelators. Representative HPs have been shown to be potential aluminum chelators by use of in vitro test systems. This study was conducted to determine systemic availability of representative HPs in rabbits prior to studies of their oral efficacy as aluminum chelators. Each of 12 rabbits was administered 0.45 mmol/kg 1,2-dimethyl- (CP20; L1) and of 1,2-diethyl-3-hydroxypyridin-4-one (CP94; EL1NEt) by gastric lavage and by injection into a lateral ear vein. Each rabbit received both compounds via both routes with at least 7 days between doses. Blood samples (1.5 ml) were collected up to 24 hr after dosing. The HPs were extracted, then analyzed by HPLC with a column packed with graphitized carbon. The mean (+/- SD) systemic clearance, steady-state volume of distribution, mean residence time, mean oral absorption time, and systemic availability for CP20 and CP94 were 0.8 +/- 0.3 and 2.1 +/- 1.4 liter/hr/kg; 1.2 +/- 0.5 and 1.2 +/- 0.5 liter/kg; 1.7 +/- 0.7 and 0.7 +/- 0.3 hr; 0.9 +/- 1.6 and 0.6 +/- 0.5 hr; and 72 +/- 20 and 57 +/- 27%, respectively. Rabbits demonstrated fairly good absorption and rapid elimination of 1,2-dimethyl- and 1,2-diethyl-3-hydroxypyridin-4-one.

Increased age affects properties characterizing behavioral plasticity in freely behaving Aplysia

In the marine mollusc Aplysia, in vitro studies showed that the gill withdrawal reflex (GWR) and its neuronal substrates were altered by age. In contrast, age minimally affected the gill respiratory pumping movements (GPM) and its neuronal substrates. Based on the respective properties of the GWR- and GPM-pathways in vitro, we proposed that the more pronounced the effect of age, the greater the expression of plasticity in a pathway. This conclusion may hold for in vitro preparations, but it remained to be demonstrated in intact animals. Based on this conclusion, the GWR should exhibit greater plasticity than the GPM in intact animals. Using freely behaving Aplysia, we tested for plasticity of the GWR and the GPM in three age groups (young, mature, and old). The tests for behavioral plasticity were: Graded responses to varying stimulus strength, response decrement (or habituation) to repetitive stimulation, enhanced response to dishabituating stimuli, and the effect of the GWR stimulus on the GPM and the GPM stimulus on the GWR. The GWR in mature animals exhibited all four properties, but in old animals, graded responses and habituation were significantly altered and in young animals habituation and dishabituation were absent. The GPM exhibited fewer of the properties than the GWR, only graded responses and response decrement, both of which were generally the same in the three groups. We found that behavioral plasticity and age-induced plasticity are related in freely behaving animals and are consistent with in vitro findings. The effect of age on properties characterizing plasticity at both the behavioral and pathway levels is discussed.

Age sensitivity of osmoregulation and of its neural correlates in Aplysia

Osmoregulation was studied in the marine mollusc Aplysia californica in young, mature, and old adults. To monitor volume and osmoregulation, we measured body weight, hemolymph osmolality, and chloride concentration. These parameters were measured at regular intervals with animals in 90% artificial seawater (90% ASW) for up to 36 h. They showed that the rates at which Aplysia osmo- and volume regulate were significantly slowed with increased age. However, no age effect was found in osmoregulation when the hemolymph was diluted to 90% of control in animals without an external stress, i.e., by injection of distilled H2O and keeping animals in 100% ASW. Because the dilution bypassed the sensory receptors that detect external changes of osmolality, this finding suggested that the slowed osmoregulation involved age-impaired functioning of the neural pathway mediating osmoregulation. Other evidence was from mature adults whose osmoreceptive organ, the osphradium, was lesioned; they mimicked osmoregulation measured in old adults. In preparations containing a portion of the osmoregulatory pathway, the osphradium was stimulated by 90% ASW, and the responsiveness of neuron R15, which putatively regulates antidiuresis, was tested. The stimulus inhibited spiking in R15 from mature adults but not in R15 from old adults or from osphradiallesioned mature ones. In old Aplysia the refractoriness of R15 to osphradial stimulation demonstrated that the effecacy of the pathway was impaired with increased age; it helped explain the slower rate of osmoregulation. Possible changes of osmoregulatory mechanisms and behavior compensating for the age sensitivity of osmoregulation are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the autonomic nervous control of the heart during classical aversive vs appetitive conditioning in dog

Dogs were trained in either classical (i.e. Pavlovian) appetitive (n = 7) or aversive (n = 7) conditioning by presenting a tone (the conditional stimulus, CS +) that was followed by either food or shock delivery, respectively. In the first case, dog food was given to the animals during the last 30 s of a 1 min CS+. Aversive conditioning was accomplished by giving a 1 s shock at the end of a 30 s CS+. The control consisted of a different tone (CS-) which was never followed by food or shock. A chronically implanted transducer was used to record left ventricular pressure from which its first time derivative was calculated; d(LVP)/dt was used as an index of myocardial inotropic state. Heart rate (HR) was also determined. These data were averaged over the 30 s prior to the CS+, the 30 s of the conditional stimulus tone itself, and the 30 s following shock or during food delivery. Well-trained animals evidenced changes in cardiac inotropism and chronotropism during the CS+ and also in response to unconditional shock or food; these are referred to as the conditional and unconditional cardiovascular responses, respectively. No statistically significant HR or d(LVP)/dt changes were observed during the CS-. The conditional response to food was small: relative to the pre-CS+ interval, average HR increased 11 bpm (P less than 0.05) and average d(LVP)/dt increased 309 mm Hg/s (P less than 0.01). During food delivery, HR increased by additional 23 bpm (P less than 0.01) and d(LVP)/dt increased by another 232 mm Hg/s (P less than 0.01). Beta-adrenergic blockade virtually eliminated the conditional HR and d(LVP)/dt response to food, indicating that both the chronotropic and inotropic changes during CS+ were due to elevated sympathetic drive. beta-blockade did not eliminate the unconditional HR response (+17 bpm, P less than 0.01), indicating that parasympathetic withdrawal has a mediating role in this persisting tachycardia. The conditional response to shock consisted of a 26 bpm increase in HR (P less than 0.01), while d(LVP)/dt increased 998 mm Hg/s (P less than 0.01). The beta-blockade reduced the HR conditional response to +8 bpm (NS) and essentially eliminated the increase in d(LVP)/dt. These data indicate that increases in cardiac sympathetic tone play a primary role in mediating the conditional cardiovascular response for both paradigms. Parasympathetic withdrawal, on the other hand, figures critically in mediating the unconditional response to food.

Behaviorally conditioned changes in atrio-ventricular transmission in awake dog

The purpose of this study was to examine the effects of behaviorally conditioned changes in autonomic activity on atrio-ventricular (AV) transmission in dog. To produce consistent activation of the cardiac nerves in the awake animal (n = 7), a classical appetitive conditioning paradigm was used. A conditioning trial consisted of a 30 s control period followed by one of two differing situations: (1) a 60-s conditional stimulus (CS+) tone wherein food (i.e. 'UCS' or unconditioned stimulus) was given during the last 30 s; or (2) at 30-s discriminative stimulus (CS-) tone which was never followed by food reward. Eight of each type trial were given daily until a stereotypic cardiovascular response was developed for the CS+ but not the CS-. The hemodynamic conditional response (i.e. 'CR', the response to the CS+) consisted of a moderate tachycardia (+14.5%, P less than or equal to 0.05), a small pressor response (+6.7%, P less than or equal to 0.01), and a moderate increase in the first time derivative of left ventricular pressure (+14.9%, P less than or equal to 0.01) reflecting an increase in inotropic state. The unconditional response (i.e., 'UCR', the response to the food reward) consisted of a substantial increase in HR (25.7%, P less than or equal to 0.01) above CR values while left ventricular pressure (LVP) and d(LVP)/dt increased 5.0% and 10.0% (P less than or equal to 0.01 for both) above their CR values. The effect of the conditioned changes in neural activity on the AV node was observed by pacing the atrium from 110 to 180 bpm during the first 15 s of each trial period (i.e. control, CS+, UCS). The discrepancy between the atrial pace rate and the transmitted ventricular rate is expressed as a 'mean difference score' and serves as an index of the fidelity of the AV transmission process: the smaller the difference, the closer a 1:1 ratio of atrial vs ventricular beats is approached. The relatively large mean difference score for the control periods (46.0 +/- 9 bpm) indicates that the paced atrial impulse did not faithfully precede ventricular contraction during these periods. The mean difference significantly decreased (34.6%, P less than or equal to 0.05) during the CS+, and approached an almost 1:1 ratio (75.6% decrease from CS+ values, P less than or equal to 0.01) during food delivery. beta-Adrenergic blockade (propranolol, 1 mg/kg, i.v.) eliminated the changes in mean difference during the CS+ but not during food delivery. There were no statistically significant physiological changes during CS-.(ABSTRACT TRUNCATED AT 400 WORDS)