Beta-agonist-induced alterations in organ weights and protein content: comparison of racemic clenbuterol and its enantiomers

A LC-MS/MS method for determination of clenbuterol enantiomers in animal tissues and its application to the enantioselective distribution in Bama mini-pigs

OBJECTIVES

To establish and validate a simple and reliable analytical method for separation and determination of clenbuterol enantiomers (R-(-)-clenbuterol & S-(+)-clenbuterol) in animal tissues, and apply it to the enantioselective distribution of clenbuterol in Bama mini-pigs.

METHODS

A LC-MS/MS analytical method was developed and validated in positive multiple reaction monitoring mode with electrospray ionization. After perchloric acid deproteinization, samples were pretreated only by one step liquid-liquid extraction using tert-butyl methyl ether under strong alkaline condition. Teicoplanin was used as chiral selector and 10 mM ammonium formate methanol solution was used as mobile phase. The optimized chromatographic separation conditions were completed in 8 min. Two chiral isomers in 11 edible tissues from Bama mini-pigs were investigated.

RESULTS

R-(-)-clenbuterol and S-(+)-clenbuterol can be baseline separated and accurately analyzed with a linear range of 5-500 ng/g. Accuracies ranged from -11.9-13.0% for R-(-)-clenbuterol and -10.2-13.2% for S-(+)-clenbuterol, intra-day and inter-day precisions were between 0.7 and 6.1% for R-(-)-clenbuterol and 1.6-5.9% for S-(+)-clenbuterol. R/S ratios in edible tissues of pigs were all significantly lower than 1.

CONCLUSIONS

The analytical method has good specificity and robustness in determination of R-(-)-clenbuterol and S-(+)-clenbuterol in animal tissues, and can be used as a routine analysis method for food safety and doping control. There is a significant difference in R/S ratio between pig feeding tissues and pharmaceutical preparations (racemate with R/S ratio of 1), which makes it possible to identify the source of clenbuterol in doping control and investigation.

Determination of Salbutamol Residues in Goat Various Tissues After Exposure to Growth-promoting Doses

In order to monitor salbutamol (SAL) use in goats as a repartitioning, we determined SAL residues in various tissues of goats after repeated oral SAL administration at a dose of 0.15 mg/kg daily for 21 days. SAL concentrations were measured by ultra performance liquid chromatography tandem mass spectrometry in extracts of tissues from goats sacrificed 0.25, 1, 3, 7, 14, 21 and 28 days after the last dose. Our results showed that on Day 0.25 of the withdrawal period, the residual proportions of SAL (expressed as percentage) in liver, kidney, lung, hair, stomachs and muscle were 19.5%, 15.3%, 3.3%, 9.6%, 28.2% and 0.8%, respectively. As the withdrawal time increased, the SAL concentrations in most tissues (except hair) decreased rapidly over the first 3 days and more slowly in the following 25 days. After a 28-day withdrawal period, hair, lung, muscle, liver, fat, eyes, rumen, kidney and abomasum still contained ~32.3%, 15.3%, 7.1%, 6.5%, 5.6%, 1.5%, 0.8% and 0.5% compared to the initial residual concentrations determined on Day 0.25, respectively. On withdrawal Day 28, the highest concentrations of SAL were found in hair (16.58 ± 9.48 μg/kg), followed by liver (7.01 ± 0.94 μg/kg), lung (2.81 ± 1.23 μg/kg), kidney (0.64 ± 0.56 μg/kg), whereas the concentrations in other tissues were lower than limit of quantification (0.50 μg/kg). SAL residues were not detected in bile, plasma and brain on Days 7, 7 and 3 after discontinuation of dosing. These findings indicated that the distribution and depletion rates of SAL differed between tissues. It should be noted that SAL residues in stomach were higher than those in muscles during the early withdrawal. We conclude that hair is the preferred tissue to monitor the administration of SAL to living goats, whereas liver can be used to monitor SAL in the carcass for determination of compliance with food safety regulation.

Distribution and Depletion of Ractopamine in Goat Plasma, Urine and Various Muscle Tissues

This study investigated the ractopamine (RAC) distribution and depletion process in goat plasma, urine and various muscle tissues which were associated with a potential risk for consumer health. The experiment was carried out in 21 goats (18 treated and 3 controls). Treated animals were administered orally a dose of 1 mg/kg body mass per day for 28 consecutive days and randomly sacrificed on Days 0.25, 1, 3, 7, 14 and 21 of the withdrawal period. RAC in goat samples was analyzed by using ultra-high performance liquid chromatography-quadrupole-orbitrap high-resolution mass spectrometry. RAC was below the limits of detection (LOD = 0.15 ng/mL) in plasma while which was higher than the LOD in urine on withdrawal day 21. The residues in goat longissimus dorsi muscle, biceps femoris muscle and triceps surae muscle were differed significantly. These findings demonstrated that urine can be used as the target matrix for monitoring RAC abuse in goat.

Clenbuterol Distribution and Residues in Goat Tissues After the Repeated Administration of a Growth-Promoting Dose

This study was conducted to investigate the deposition and depletion process of clenbuterol (CL) in goat tissues, plasma and urine after the repeated administration of a growth-promoting dose. The experiment was conducted in 24 goats (21 treated and 3 controls). Treated animals were administered orally in a dose of 16 µg/kg body mass once daily for 21 consecutive days and randomly sacrificed on days 0.25, 1, 3, 7, 14, 21 and 28 of the withdrawal period. CL in goat tissues was extracted with organic solvents and determined using liquid chromatography tandem mass spectrometry. The depletion rates of tissue differed significantly. The highest concentrations of CL in all tissues are detected on day 0.25 of treatment discontinuation. After administration had been discontinued for 28 days, CL still residues in all tissues, especially, in whole eye, where the concentrations reach 363.29 ± 31.60 μg/kg. These findings confirmed that the whole eye, which are rich in pigment, showed a much higher concentration than any other studied tissue during the withdrawal period.

Enantioselective disposition of clenbuterol in rats

Clenbuterol is a long-acting β2-adrenoceptor agonist and bronchodilator that is used for the treatment of asthma, but the desired activities reside almost exclusively in the (-)-R-enantiomer. This study examined enantioselectivity in the disposition of clenbuterol following administration of clenbuterol racemate to rats. Concentrations of clenbuterol enantiomers in plasma, urine and bile were determined by LC-MS/MS assay with a Chirobiotic T column. This method was confirmed to show high sensitivity, specificity and precision, and clenbuterol enantiomers in 0.1 ml volumes of plasma were precisely quantified at concentrations as low as 0.25 ng/ml. The pharmacokinetic profiles of clenbuterol enantiomers following intravenous and intraduodenal administration of clenbuterol racemate (2 mg/kg) in rats were significantly different. The distribution volume of (-)-R-clenbuterol (9.17 l/kg) was significantly higher than that of (+)-S-clenbuterol (4.14 l/kg). The total body clearance of (-)-R-clenbuterol (13.5 ml/min/kg) was significantly higher than that of the (+)-S-enantiomer (11.5 ml/min/kg). An in situ absorption study in jejunal loops showed no difference in the residual amount between the (-)-R- and (+)-S-enantiomers. Urinary clearance was the same for the two enantiomers, but biliary excretion of (-)-R-clenbuterol was higher than that of the (+)-S-enantiomer. The fractions of free (non-protein-bound) (-)-R- and (+)-S-clenbuterol in rat plasma were 48.8% and 33.1%, respectively. These results indicated that there are differences in the distribution and excretion of the clenbuterol enantiomers, and these may be predominantly due to enantioselective protein binding.

Enantioselective disposition of (R/S)-albuterol in skeletal and cardiac muscle

Significant enhancement of skeletal muscle function has been observed with racemic albuterol (salbutamol). There is now general acceptance that the R-albuterol enantiomer elicits the pharmacological response, both in the lungs and extrapulmonary, while S-albuterol is pharmacologically inert. The objective of this study was to investigate the distribution of (R/S)-albuterol enantiomers into skeletal and cardiac muscle. Initially oral dosing was undertaken in neonatal mice administered a maximum tolerable dose of racemic albuterol. An in vivo infusion rat model was employed for the investigation of albuterol uptake into skeletal and cardiac muscle over 4 h. Tissue concentrations were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). From the oral dosing model, mean (±SD) levels of racemic albuterol after 5 days were 915 (±293) ng/mL in plasma, 2574 (±196) ng/g in muscle, and 53 (±6.6) ng/g in brain with enantioselective partitioning (muscle:plasma ratio of 5.7 and 1.7 for R- and S-albuterol, respectively). In the infusion model, enantioselective disposition was observed in skeletal muscle (muscle:plasma ratio of 1.2-1.7 and 0.6-0.7 for R- and S-albuterol, respectively) and in cardiac muscle (4.1 and 0.5, respectively). In conclusion, there is greater partitioning of active (R)-albuterol than inactive (S)-albuterol into both skeletal and cardiac muscle compared to plasma. These findings have relevance for albuterol sports doping, cardiac effects, and therapeutic use in muscle wasting diseases. Furthermore, the greater muscle partitioning of the active R-albuterol, and the availability of pure R-albuterol formulations highlight shortcomings in doping control measures using non-enantioselective assays.

Does the analysis of the enantiomeric composition of clenbuterol in human urine enable the differentiation of illicit clenbuterol administration from food contamination in sports drug testing?

RATIONALE

Clenbuterol (4-amino-α-[(tert-butylamino)methyl]-3,5-dichlorobenzyl alcohol) is approved for human and veterinary use primarily for the treatment of pulmonary afflictions. Despite the authorized administration in cases of medical indications, the misuse of clenbuterol in animal husbandry as well as elite and amateur sport has frequently been reported, arguably due to growth-promoting properties. Due to various recent incidences of doping control specimens containing clenbuterol, strategies towards the discrimination of a surreptitious application from unintended intake via animal-derived edibles or dietary supplements were required.

METHODS

The enantiomeric compositions of clenbuterol in human urine samples derived from administration studies with therapeutic amounts of the β(2)-agonist and authentic doping control specimens were determined. Due to the facts that therapeutic clenbuterol consists of a racemic mixture of (+)- and (-)-stereoisomers and that the first mentioned (dextrorotatory) stereoisomer is retained to a greater extent in edible animal tissue, the differentiation of a recent administration of therapeutic (and thus racemic) clenbuterol from food contamination (stereoisomerically depleted clenbuterol) was considered. Employing deuterated clenbuterol as internal standard, the target analytes were extracted from human urine by means of concerted liquid-liquid and solid-phase extractions and subjected to chiral liquid chromatography hyphenated to high resolution/high accuracy mass spectrometry with electrospray ionization.

RESULTS

Both enantiomers of clenbuterol were baseline separated and relative abundances of corresponding labeled and unlabeled stereoisomers were determined, demonstrating that the therapeutic use of clenbuterol results in racemic mixtures in urine for at least 24 h while adverse analytical findings presumably originating from food contaminations can yield (-)-clenbuterol-depleted pairs of analytes.

CONCLUSIONS

The determination of relative abundances of clenbuterol enantiomers can indicate the ingestion of clenbuterol via contaminated food; however, depletion of (-)-clenbuterol in edible animal tissue is time-dependent and thus results can still be inconclusive as to the inadvertent ingestion of clenbuterol when clenbuterol administration to animals was conducted until slaughter.

The effects of R-salbutamol on growth, carcass measures, and health of finishing pigs

A pure form of salbutamol has the potential to deliver positive production benefits to the swine industry. The aim of this experiment was to determine the effects of salbutamol on growth, carcass measures, and health of finishing pigs. The study used 192 pigs (89 ± 1 kg BW) housed in groups of 6 in 32 pens and assigned to 1 of 4 treatments: 1) control (CTL), 0 mg/kg salbutamol; 2) 2R, control diet with 2 mg/kg of the pure R-enantiomer of salbutamol; 3) 4R, control diet with 4 mg/kg of pure R-salbutamol; or 4) 8RS, control diet with 8 mg/kg of a 50:50 mixture of the R- and S-enantiomers. All diets were offered ad libitum for 4 wk. All pigs were weighed and pen feed intakes were recorded weekly. At slaughter, individual HCW and measurements of the 10th-rib loin muscle area (LMA), color, marbling, firmness, and back fat, last lumbar, and midline back fat depths were collected. Data were analyzed using Proc GLM of SAS, with pen as the experimental unit. Overall, 2R and 4R pigs had greater ADG than CTL pigs (P < 0.05) and, at slaughter, were heavier than CTL pigs (P < 0.01). Overall, 8RS pigs had decreased ADFI (P < 0.05), and CTL pigs had poorer G:F (P < 0.001) than the other 3 treatments. All salbutamol-fed pigs had 5 to 6 kg greater HCW (P < 0.001), 2% to 3% increased carcass yield (P < 0.001), 5.6 cm(2) larger LMA (P < 0.01), 3 to 4 mm less 10th-rib back fat (P < 0.01), and 2 mm less lumbar back fat (P < 0.05) than CTL pigs. However, control pigs had greater loin muscle color scores (P < 0.05) and marbling scores (P < 0.001) than all salbutamol-treated pigs. Taken together, these data indicate that as little as 2 mg/kg R-salbutamol has a positive effect on pig growth and carcass composition. However, the effects of salbutamol on meat quality require further research.

Effects of clenbuterol, a β₂-adrenergic agonist, on sizes of masseter, temporalis, digastric, and tongue muscles

We compared the hypertrophic effects of clenbuterol, a β₂-adrenergic agonist, on the masseter, digastric, and temporalis with those on the tongue, tibialis anterior, soleus, diaphragm, and heart. The weights of masseter, digastric and temporalis in the clenbuterol group were 36 ~ 56% greater than those in the control group, whereas those of the tibialis anterior, diaphragm, and heart weights in the clenbuterol group were 9 ~ 33% greater than those in the control group. No significant difference in the weights of the soleus and tongue was found between the control and clenbuterol groups. Taken together with our present and previously reported results, it is suggested that the hypertrophic effects of clenbuterol on the masseter, digastric, and temporalis are greater than those on the limb, trunk, and heart.

Comparison of enantiomers of SPFF, a novel beta2-Adrenoceptor agonist, in bronchodilating effect in guinea pigs

Previous study on racemic SPFF [2-(4-amino-3-chloro-5-trifluomethyl-phenyl)-2-tert-butylamino-ethanol hydrochloride], a novel beta2-adrenoceptor agonist, has validated that it is a potent, long-acting bronchodilator with relative higher beta2-adrenoceptor selectivity. On the basis of this study, we compared the pharmacological properties of SPFF and its enantiomers ((-)-SPFF and (+)-SPFF) in guinea pigs taking isoprenaline or salbutamol (SAB) as referenced drugs. For the relaxation of both normal and precontracted trachea strips in vitro, (-)-SPFF was found more potent than (+/-)-SPFF or (+)-SPFF. Moreover, we confirmed that the bronchodilator effect of (-)- and (+)-enantiomers were due to activation of the beta2-adrenoceptor because this effect was antagonized by a specific beta2-adrenoceptor antagonist, ICI-118551, with similar pA2 values to those of (+/-)-SPFF. Radioligand binding assay revealed that affinity of (-)-enantiomer to beta2-adrenoceptor was 6 and 164 fold greater than that of (+/-)- and (+)-SPFF, respectively. In addition, isomeric difference of overall selectivity between (-)-SPFF and (+)-SPFF was 10.7 fold for lung versus atria. (-)-SPFF displayed almost the same protective effect against bronchospasm induced by histamine-acetylcholine aerosol in conscious guinea pigs as (+/-)-SPFF did. However, the latent time of (+)-SPFF (1 mg.kg(-1)) was significantly shorter than that of (+/-)- and (-)-SPFF at the same doses. Finally, in the inhibition of histamine-induced increase of pulmonary resistance (RL) in anesthetized guinea pigs, (-)-SPFF was 1.3 and 3.5 times more potent than (+/-)- and (+)-SPFF. Correspondingly, in inhibiting the decrease of pulmonary compliance (CL) , the potencies of (-)- and (+)-enantiomers were approximately equivalent to that of (+/-)-SPFF. Furthermore, a study on the long-lasting action of the test drugs had shown that the effects of (-)-SPFF (30 microg.kg(-1)), (+/-)-SPFF (30 microg.kg(-1)) and (+)-SPFF (100 microg.kg(-1)) in inhibiting the increase of RL all lasted for 4 h. Nevertheless, the effects of (-)- and (+)-enantiomers were slightly lower 4 h after intraduodenal administration in inhibiting the decrease of CL. In conclusion, (-)-SPFF may be beneficial for the treatment of asthma because of its more potent efficacy and higher adrenoceptor affinity than (+/-)- or (+)-SPFF.

Enantio-selective effects of clenbuterol in cultured neurons and astrocytes, and in a mouse model of cerebral ischemia

Neuroprotective effects of the lipophilic beta(2)-adrenoceptor agonist clenbuterol have been established in neuronal cultures and in various rodent models of stroke. In previous studies, however, clenbuterol was always applied as a racemate, while it has not been established whether the enantiomers differ in their neuroprotective activities. Here, we demonstrate that R,S-clenbuterol and S(+)-clenbuterol, but not the R(-)-enantiomer protect cultured neurons against glutamate-mediated excitotoxicity and staurosporine-induced apoptosis. Similar to previous findings with clenbuterol racemate, the neuroprotective effect of S(+)-clenbuterol correlated well with morphological changes of astrocytes which transformed into dense stellate cells with dendritic processes indicating beta(2)-adrenoceptor-mediated activation. Most importantly, the S(+)-enantiomer but not R(-)-clenbuterol reduced ischemic brain damage similar to the effect of the racemate. The selective beta(2)-adrenoceptor antagonist butoxamine blocked this neuroprotective effect of S(+)-clenbuterol. In addition, S(+)-clenbuterol significantly reduced blood pressure, enhanced blood glucose levels and increased glucocorticoid levels compared to vehicle-or R(-)-clenbuterol-treated controls. These results clearly demonstrate that S(+)-clenbuterol is the eutomer that mediates neuroprotective effects of the beta(2)-adrenoceptor agonist but also according changes of physiological parameters.

β-Agonists enhance the lactic dehydrogenase (LDH) expression in serum and ventricular myocytes of mice

Beta-agonists have skeletal muscle specific protein anabolic effects and are also known to cause cardiac hypertrophy. Changed total LDH and its isozymic patterns are conveniently employed for the detection of different pathophysiological states of the tissues. The purpose of this study is to confirm total LDH and its isozymic expression in ventricular tissue and serum in mice following oral administration of single but higher dose of isoproterenol (Iso) and clenbuterol (Cl) (100 mg/kg body wt. and 20 mg/kg body wt., respectively), after 4, 8 and 20 hours of drug administration. Mice heart witnessed increased total LDH levels with time. Serum on the other hand showed decline in total LDH concentrations at the initial points of the drug treatment. No doubt, total LDH expression increased towards 20th h post-drug treatment but this increase is mainly due to anaerobic isozymes, i.e. LDH4 and LDH5. The findings of the present study suggest that tissue damage is definitely caused by two beta-agonists after giving single dose for shorter time span (20 hours) and the impact of the damage varies from drug to drug. Increase in total LDH in serum is not due to release from heart but from some other tissues having anaerobic metabolism.

Dose-dependent separation of the hypertrophic and myotoxic effects of the beta(2)-adrenergic receptor agonist clenbuterol in rat striated muscles

Muscle growth in response to large doses (milligrams per kilogram) of beta(2)-adrenergic receptor agonists has been reported consistently. However, such doses may also induce myocyte death in the heart and skeletal muscles and hence may not be safe doses for humans. We report the hypertrophic and myotoxic effects of different doses of clenbuterol. Rats were infused with clenbuterol (range, 1 microg to 1 mg.kg(-1)) for 14 days. Muscle protein content, myofiber cross-sectional area, and myocyte death were then investigated. Infusions of >or=10 microg.kg(-1).d(-1) of clenbuterol significantly (P<0.05) increased the protein content of the heart (12%-15%), soleus (12%), plantaris (18%-29%), and tibialis anterior (11%-22%) muscles, with concomitant myofiber hypertrophy. Larger doses (100 microg or 1 mg) induced significant (P<0.05) myocyte death in the soleus (peak 0.2+/-0.1% apoptosis), diaphragm (peak 0.15+/-0.1% apoptosis), and plantaris (peak 0.3+/-0.05% necrosis), and significantly increased the area fraction of collagen in the myocardium. These data show that the low dose of 10 microg.kg(-1).d(-1) can be used in rats to investigate the anabolic effects of clenbuterol in the absence of myocyte death.

Dose-dependent apoptotic and necrotic myocyte death induced by the beta2-adrenergic receptor agonist, clenbuterol

We have investigated the dose- and time-dependency of myocyte apoptosis and necrosis induced by the beta2-adrenergic receptor agonist, clenbuterol, with the aim of determining whether myocyte apoptosis and necrosis are two separate processes or a continuum of events. Male Wistar rats were administered subcutaneous injections of clenbuterol, and immunohistochemistry was used to detect myocyte-specific apoptosis and necrosis. Myocyte apoptosis peaked 4 h after, and necrosis 12 h after, clenbuterol administration. In the soleus, peak apoptosis (5.8 +/- 2.0%; P < 0.05) was induced by 10 mug and peak necrosis (7.4 +/- 1.7%; P < 0.05) by 5 mg x kg(-1) clenbuterol. Twelve hours after clenbuterol administration, 73% of damaged myocytes labeled as necrotic, 27% as apoptotic and necrotic, and 0% as purely apoptotic. Administrations of clenbuterol (10 microg x kg(-1)) at 48-h intervals induced cumulative myocyte death over 8 days. These data show that the phenotype of myocyte death is dependent on the magnitude of the insult and the time at which it is investigated. Only very low doses induced apoptosis alone; in most cases apoptotic myocytes lysed and became necrotic and the magnitude of necrosis was greater than that of apoptosis. Thus, it is important to investigate both apoptotic and necrotic myocyte death, contrary to the current trend of only investigating apoptotic cell death.

Effects of chronic administration of clenbuterol on function and metabolism of adult rat cardiac muscle

Clenbuterol (Clen), a β2-agonist, is known to produce skeletal and myocardial hypertrophy. This compound has recently been used in combination with left ventricular assist devices for the treatment of end-stage heart failure to reverse or prevent the adverse effects of unloading-induced myocardial atrophy. However, the mechanisms of action of Clen on myocardial cells have not been fully elucidated. In an attempt to clarify this issue, we examined the effects of chronic administration of Clen on Ca2+ handling and substrate preference in cardiac muscle. Rats were treated with either 2 mg·kg−1·day−1 Clen or saline (Sal) for 4 wk with the use of osmotic minipumps. Ventricular myocytes were enzymatically dissociated. Cells were field stimulated at 0.5, 1, and 2 Hz, and cytoplasmic Ca2+ transients were monitored with the use of the fluorescent indicator indo-1 acetoxymethyl ester. Two-dimensional surface area and action potentials in current clamp were also measured. We found that in the Clen group there was significant hypertrophy at the organ and cellular levels compared with Sal. In Clen myocytes, the amplitude of the indo-1 ratio transients was significantly increased. Sarcoplasmic reticulum Ca2+ content, estimated by rapid application of 20 mM caffeine, was significantly increased in the Clen group. The action potential was prolonged in the Clen group compared with Sal. Carbohydrate contribution to the tricarboxylic cycle (Krebs cycle) flux was increased several times in the Clen group. This increase was associated with decreased expression of peroxisome proliferator-activated receptor-α. This study shows that chronic administration of Clen induces cellular hypertrophy and increases oxidative carbohydrate utilization together with an increase in sarcoplasmic reticulum Ca2+ content, which results in increased amplitude of the Ca2+ transients. These effects could be important when Clen is used in conjunction with left ventricular assist devices treatment.

Changes in muscle proteins and spermidine content in response to unloading and clenbuterol treatment

Anabolic agents such clenbuterol (Cb) are useful tools for probing the mechanisms by which muscles respond to disuse. Cb was examined under different loading conditions with respect to its effects on muscle mass, protein (myofibrillar and cytosolic), and spermidine content in mature male rats. Compared with control treatment, Cb significantly increased loaded and unloaded soleus, plantaris, and extensor digitorum longus (EDL) mass. Likewise, Cb significantly increased loaded and unloaded soleus (24.8 and 21.6%, respectively), plantaris (12.1 and 22.9%, respectively), and EDL (22.4 and 13.3%, respectively) myofibrillar protein content. After unloading, cytosolic proteins significantly increased in the EDL but decreased in the soleus and plantaris. Cb significantly increased cytosolic protein levels in all loaded muscles, while only causing increases in unloaded soleus. When compared with controls, unloading caused significant reductions in spermidine levels in the soleus (40.4%) and plantaris (35.9%) but caused increases in the EDL (54.8%). In contrast, Cb increased spermidine levels in unloaded soleus (42.9%), plantaris (102.8%), and EDL (287%). In loaded muscles, Cb increased spermidine levels in all three muscles, but to a lesser degree than under unloading conditions. Nonlinear regression analyses indicated that the plantaris behaves like a slow-twitch muscle under unloading conditions and like a fast-twitch muscle when loaded. This suggests that the responses of these muscles to unloading and (or) Cb treatment might be influenced by factors beyond fiber type alone.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Myotoxic effects of clenbuterol in the rat heart and soleus muscle

Myocyte-specific necrosis in the heart and soleus muscle of adult male Wistar rats was investigated in response to a single subcutaneous injection of the anabolic beta(2)-adrenergic receptor agonist clenbuterol. Necrosis was immunohistochemically detected by administration of a myosin antibody 1 h before the clenbuterol challenge and quantified by using image analysis. Clenbuterol-induced myocyte necrosis occurred against a background of zero damage in control muscles. In the heart, the clenbuterol-induced necrosis was not uniform, being more abundant in the left subendocardium and peaking 2.4 mm from the apex. After position (2.4 mm from the apex), dose (5 mg clenbuterol/kg), and sampling time (12 h) were optimized, maximum cardiomyocyte necrosis was found to be 1.0 +/- 0.2%. In response to the same parameters (i.e., 5 mg of clenbuterol and sampled at 12 h), skeletal myocyte necrosis was 4.4 +/- 0.8% in the soleus. These data show significant myocyte-specific necrosis in the heart and skeletal muscle of the rat. Such irreversible damage in the heart suggests that clenbuterol may be damaging to long-term health.

Biological actions of formoterol isomers

Racemic beta(2) agonists, composed of equal amounts of (R)- and (S)-isomers, can display anomalous actions that compromise their effectiveness as asthma therapies. Loss of efficacy during regular use is characteristic of isoprenaline, albuterol and terbutaline and has in part been attributed to the biological effects of the (S)-isomer. This hypothesis was applied to the (R,R)- and (S,S)-isomers of formoterol. (R,R)-formoterol had 1000-times greater affinity (2.9 nm) to the human beta(2) adrenoceptor than (S,S)-formoterol (3100 nm), with receptor binding modulating intracellular cAMP levels. The minimum lethal intravenous (IV) dose was determined to be 100 mg/kg for (R,R)- and 50 mg/kg for (S,S)-formoterol, suggesting that the toxicity of (S,S)-formoterol may not be related to the binding of beta(2) adrenoceptors. In tissues pretreated with (S,S)-formoterol but not with (R,R)- or racemic formoterol contractions to high concentrations of carbachol were exaggerated. In vivo experiments with sensitized guinea pigs demonstrated that (R,R)-formoterol inhibited both histamine and antigen-induced bronchoconstriction with greater potency than (R,R/S,S)-formoterol while (S,S)-formoterol was ineffective. Metabolic radiolabeling experiments of (R,R)-, (S,S)- or (R,R/S,S)-formoterol with crude human liver phenolsulfotransferase (PST) determined the V(max)/K(m) values to be (0.151), (0.74) and (0.143), respectively. The reciprocal plot illustrates a 2-fold reduction in sulfation rate when (R,R)-formoterol is present as a single isomer. The data presented here suggest that (R,R)-formoterol binds to the beta(2) adrenoceptor and inhibits the contraction of bronchial tissues by spasmogens. However, (S,S)-formoterol exhibits properties inconsistent as an asthma therapeutic and may antagonize the actions of (R,R)-formoterol.

Recent applications of stereoselective chromatography

Some recent applications of stereoselective chromatography in the fields of clinical pharmacy, drug analysis, food, and natural products are reviewed. The review is documented with up-to-date literature, which will assist further expansion of research in these areas.

Alteration of contractile force and mass in the senescent diaphragm with beta(2)-agonist treatment

Aging is associated with a decrease in diaphragmatic maximal tetanic force production (P(o)) in senescent rats. Treatment with the beta(2)-agonist clenbuterol (CB) has been shown to increase skeletal muscle mass and P(o) in weak locomotor skeletal muscles from dystrophic rodents. It is unknown whether CB can increase diaphragmatic mass and P(o) in senescent rats. Therefore, we tested the hypothesis that CB treatment will increase specific P(o) (i.e., force per cross-sectional area) and mass in the diaphragm of old rats. Young (5 mo) and old (23 mo) male Fischer 344 rats were randomly assigned to one of the following groups (n = 10/group): 1) young CB treated; 2) young control; 3) old CB treated; and 4) old control. Animals were injected daily with either CB (2 mg/kg) or saline for 28 days. CB increased (P < 0.05) the mass of the costal diaphragm in both young and old animals. CB treatment increased diaphragmatic-specific P(o) in old animals (approximately 15%; P < 0.05) but did not alter (P > 0.05) diaphragmatic-specific P(o) in young animals. Biochemical analysis indicated that the improved maximal specific P(o) in the diaphragm of CB-treated old animals was not due to increased myofibrillar protein concentration. Analysis of the myosin heavy chain (MHC) content of the costal diaphragm revealed a CB-induced increase (P < 0.05) in type IIb MHC and a decrease in type I, IIa, and IIx MHC in both young and old animals. These data support the hypothesis that CB treatment can restore the age-associated decline in both diaphragmatic-specific P(o) and muscle mass.