Effects of clenbuterol as a repartitioning agent on beta-adrenoceptor concentrations in heart, bronchi and brain of veal calves

New insights into cytotoxicity induced by microcystin-LR, estradiol, and ractopamine with mathematical models: Individual and combined effects

Humans are most likely to be exposed to microcystins (MCs) combined with other water pollutants rather than to individual compounds through the consumption of contaminated drinking water or through recreational activities, such as swimming. However, the combined effects of MC-LR, estradiol (EST), and ractopamine (RAC) have not been extensively researched. The goal of this study was to investigate the combined effects of these compounds. For this purpose, cytotoxicity was evaluated in HepG2 cells treated with single or combined doses of MC-LR, EST, and RAC based on concentration addition (CA), independent action (IA), and Chou-Talalay's combination-index (CI) methods. Singly applied MC-LR and EST induced HepG2 cellular proliferation at low-concentration levels (1 × 10^-12-1 × 10^-9 M), and decreased viability at higher doses of exposure (1 × 10^-9-1 × 10^-6 M). Exposure to binary or ternary mixtures of MC-LR, EST, and RAC exhibited synergistic effects at high concentrations, irrespective of the models used. In contrast, antagonism was observed for the mixture of MC-LR and EST at relatively low concentrations. A synergistic effect on reactive oxygen species (ROS) generation was observed for the combined drugs at high concentrations. Additionally, the ratio of apoptotic cells was increased more by the combined drugs than the single drugs, consistent with the inhibition of cell viability. The ROS increase after treatment with the combined drugs may enhance cytotoxicity and subsequently lead to cell apoptosis. Given the interactions between MC-LR, EST, and RAC, government regulatory standards for MC-LR should consider the toxicological interactions between MC-LR and other environment pollutions.

Investigation on potential enzyme toxicity of clenbuterol to trypsin

Clenbuterol (CLB) is a kind of β2-adrenergic agonists which was illegally used as feed additives nowadays. The toxic interaction of CLB with trypsin, an important digestive enzyme, was studied in vitro using multi-spectroscopic methods and molecular modeling methods. CLB was proved to bind with trypsin in S1 pocket, forming a complex driven by the dominant force of H-bond. The binding constant was calculated to be 1.79887×10(5) L mol(-1) at 289 K and 0.32584×10(5) L mol(-1) at 310 K, respectively. The skeleton of trypsin became loosened and unfolded with the amino residues microenvironment changed. The secondary and tertiary structure of trypsin also varied. Molecular modeling studies illustrated specific display of the binding information and explained most of the experiment phenomena. The binding site of CLB induced the fluorescence quenching as well as inhibition of enzyme activity of trypsin. The study confirmed that CLB had potential toxicity on both the structure and function of trypsin and the effects enhanced with the increasing concentration of CLB.

Effects of the β2 -agonist clenbuterol on testicular steroidogenic acute regulatory protein mRNA expression in adult rats

This study was carried out to investigate the effects of clenbuterol (CLB) on the testicular (steroidogenic acute regulatory, StAR) protein mRNA expression in rats. Thirty adult male rats were administered CLB by gavage daily at the doses of 0.4, 2.0 and 18.5 mg/kg bw for 14 days in the subacute experiment, whereas 20 rats received a single treatment with CLB at the doses of 20 and 40 mg/kg bw in the acute experiment and 20 rats were treated with 0.9% NaCl solution as vehicle groups. Testicular tissues were collected and snap-frozen in liquid nitrogen and stored at -70 °C until use. The levels of StAR mRNA were detected by RT-PCR. The levels of StAR mRNA were markedly increased (P < 0.05) at both dosages of 20 and 40 mg/kg bw but the effects were not dose-dependent and the mRNA levels of StAR were returned to near normal level after 7 days of CLB withdrawal, compared with the control animals. In the subacute experiment, CLB induced a dose-dependent but no statistical significant reduction (P > 0.05) in the expression levels of StAR mRNA, and the mRNA levels were recovered to near normal level in the groups treated with CLB at dosages of 0.4 and 2.0 mg/kg bw/day following a 7-day withdrawal period, compared with the control animals. The mRNA levels of StAR showed a significant decrease in the groups treated with CLB at the dosage of 18.5 mg/kg bw/day (P < 0.05) after a 1- or 7-day withdrawal period with respect to the control animals. These results demonstrated transient stimulative effects of CLB on testicular StAR mRNA levels and inhibitory effects after treatment with CLB for 14 consecutive days.

Neonatal exposure to fenoterol and betamethasone: effects on the behavioral development in the rat

We investigated longitudinally the behavioral development in the rat following exposure to beta-agonists and glucocorticoids (GC). Neonatal rats received either 1 mg/kg fenoterol (FEN), 0.3 mg/kg betamethasone (BET), or saline (SAL). Weanling and young adult rats were tested in the open field, the elevated-plus maze, and the water maze. FEN-treated as well as BET-treated animals displayed increased anxiety-like behavior. Furthermore, BET-treated adult animals showed a reduced locomotor activity. An enhanced 24-h memory in the water maze in both treatment groups may be facilitated by emotional arousal due to the increased anxiety levels. The possible neurobiological underpinnings are discussed in detail.

Dietary zilpaterol hydrochloride. I. Feedlot performance and carcass traits of steers and heifers

Experiments were conducted at 3 US locations (CA, ID, and TX) to determine the effects of dietary zilpaterol hydrochloride (Zilmax, Intervet Inc., Millsboro, DE) and duration of zilpaterol feeding on performance and carcass merit of finishing steers and heifers. At each site, 160 steers and 160 heifers were stratified within sex by initial BW (study d -1) and assigned randomly within BW strata to 1 of 4 treatments in a randomized complete block design (4 blocks/treatment for each sex). The 4 treatments were arranged in a 2 (no zilpaterol vs. zilpaterol) x 2 (20 or 40 d duration of zilpaterol feeding) factorial arrangement of treatments. When included in the diet, zilpaterol was supplemented at 8.3 mg/kg of DM. Each pen consisted of 10 animals. Each animal was individually weighed unshrunk on d 1, 21 or 41, and 66 of the experiment. Following d 66, cattle were slaughtered and carcass data collected. Feeding zilpaterol increased (P<0.01) final BW of steers and heifers by 11.6 and 6.7 kg, respectively. In addition, feeding zilpaterol hydrochloride increased (P <or= 0.001) ADG 36 and 18%, and increased (P<0.001) G:F 28 and 21% for steers and heifers, respectively. For heifers, DMI was decreased (P<0.001) 6.2% when zilpaterol was fed, whereas in steers DMI tended (P=0.09) to be decreased 2%. For steers and heifers, feeding zilpaterol increased (P<0.001) HCW 16.4 and 12.1 kg, dressing percentage 1.5 percentage units for each sex, and LM area 8.23 and 6.37 cm(2), respectively. Twelfth-rib fat (P >or= 0.12) and KPH (P >or= 0.70) were not affected by feeding zilpaterol to steers or heifers. Feeding zilpaterol decreased (i.e., improved; P=0.02) calculated yield grade of steer and heifer carcasses. Marbling score (P=0.002) and quality grade (P=0.002) were decreased when zilpaterol hydrochloride was fed to steers, and the decrease in marbling score and quality grade tended to be greater when zilpaterol was fed for 40 compared with 20 d (zilpaterol x duration interaction, P=0.07). For heifers, marbling score tended (P=0.07) to be decreased and quality grade was decreased (P=0.05) when zilpaterol hydrochloride was fed. In general, it appears from these data that zilpaterol hydrochloride fed for 20 to 40 d at the end of the finishing period enhances growth performance and carcass muscle deposition for steers and heifers.

Regulation of tissue β-adrenergic, glucocorticoid and androgen receptors induced by repeated exposure to growth promoters in male veal calves

Biochemical modifications induced by a combination of anabolic compounds in target organs of male veal calves have been evaluated. Six male Friesian crossbred calves were treated with of 17beta-estradiol, dexamethasone sodium phosphate and clenbuterol or served as controls. beta-Adrenoceptors (beta-ARs) were measured in myocardium, lung, spleen, cerebral cortex, hippocampus, thalamus, hypothalamus, and hypophysis, glucocorticoid receptors (GRs) in the spleen and androgen receptors (AnRs) in the testis, by binding assay. A significant decrease in beta-ARs was observed in all tissue samples from treated animals. In the spleen the two GR subtypes found, low (LA) and high (HA) affinity GRs, were down-regulated by the treatment. A significant (P<0.05) decrease of testis weight and a significant (P<0.05) up-regulation of AnRs was also observed. Our data demonstrate that long-term treatment with anabolic compounds markedly affects receptor concentrations in target organs of male veal calves. Thus, studies investigating biological assays as screening methods to detect such compounds should be encouraged.

The effect of long-term exposure to combinations of growth promoters in Long Evans rats: part 2. Adrenal morphology (histopathology and immunochemical studies)

The aim of the study was to investigate the effects of long-term exposure (45 days) to growth promoters: clenbuterol (CB: 1 mg kg(-1) bw) and/or dexamethasone (DEX: 0.1 mg kg(-1) bw), in adrenal gland morphology, and the possibility of recovery after the withdrawal of drug treatment. Animals were sacrificed at different days of withdrawal (W0, W5, W10, W15 and W20), and adrenal glands processed for histopathology and immunohistochemistry. Adrenals of CB treatment showed typical features of long-term administration of beta-agonists at W0 such as capillary dilatation in the fasciculata-reticularis zone, and this feature was also presented at W20. Adrenals of CB+DEX treatments showed the same results of CB treatment at days W0 and W20. However, DEX treatment presented the typical results of the exposure to corticoids with the atrophy of adrenal cortex. Immunohistochemistry of adrenal cortex steroidogenic enzymes (P450: scc, 3beta-HSD, aromatase) denoted that neither positive staining nor localization was affected by treatments. Aromatase enzyme was immunolocalized in adrenal medulla cells in controls as well as in treated groups. The immunolocalization of glucocorticoid receptors showed an increase in CB (+++) and CB+DEX (++) treatments compared to the control group (0) and DEX treatment (0). Histopathological and immunohistochemical results are closely related to those found for adrenal endocrine function. We can conclude that chronic administration of growth promoters influence adrenal morphology and glucocorticoid receptor expression.

Changes in lymphocyte glucocorticoid and beta-adrenergic receptors in veal calves treated with clenbuterol and steroid hormones for growth-promoting purposes*

In order to identify possible peripheral markers of illegal treatments with growth-promoting agents in veal calves, beta-adrenergic receptor (beta-AR) and glucocorticoid receptor (GR) concentrations were measured in lymphocytes of 12 male Friesian crossbred calves (six controls and six treated). The animals received a cocktail of anabolic and re-partitioning agents [17beta-oestradiol: 3 x 10 mg intramuscular (i.m.) doses at 17-day intervals; dexamethasone sodium phosphate: 4 mg/day for 6 days and 5 mg/day for six further days dissolved in milk; and clenbuterol: 20 microg/kg/day dissolved in milk for the last 40 days before slaughter]. Blood samples were collected by venipuncture at different time points and lymphocytes were isolated by density gradient centrifugation. Lymphocyte beta-AR and GR levels were measured by binding assays. Treatment with re-partitioning agents caused a significant down-regulation of lymphocyte beta-ARs 19 days after the beginning of clenbuterol administration and at day 55 (after dexamethasone withdrawal, just before slaughter). This phenomenon was partially reversed at day 50, after dexamethasone administration, at which time a significant decrease in GR concentrations also occurred. For both types of receptors, no significant changes in the dissociation constant values were observed at any time point. Lymphocytes express measurable concentrations of beta-ARs and GRs and the measurement of receptor levels highlights the fluctuation of receptor expression due to the dynamic interaction of the drugs used in combination. Lymphocyte receptor determination could therefore be included in a battery of biological assays to detect illegal treatments with anabolic agents in veal calves in the light of a multivariate approach.

Are so many adrenergic receptor subtypes really present in domestic animal tissues? A pharmacological perspective

Adrenergic receptors (ARs) are the cellular membrane binding sites through which natural catecholamines and sympathomimetic drugs exert their physiological and pharmacological effects. In recent decades, studies to clarify the distribution and function of ARs have been performed mostly on cultured cells, laboratory animals and human target tissues, but little is known about these aspects in domestic animals. This review focuses on AR structure, classification and signalling pathways and on AR subtype distribution in target tissues of some domestic animals, namely dogs, horses and bovines. In these species, different alpha- and beta-AR subtypes have been characterized and the functions controlled by the adrenergic systems have been studied. In the dog, the role played by the adrenergic system in the pathogenesis of cardiovascular disorders and in the modulation of canine aggression has roused particular interest. In dogs affected by dilated cardiomyopathy a significant down-regulation of beta-ARs has been observed both in the heart and circulating lymphocytes. This finding confirms the involvement of the adrenergic system in the pathogenesis and progression of the disorder and suggests new therapeutic strategies. In the horse, AR distribution has been studied in the cardiac, respiratory and gastrointestinal systems as well as in digital veins and arteries. The cardiac beta-ARs in healthy horses seem to be predominantly represented by the beta(1) subtype. In this species, heart failure may increase the expression of the beta(2) subtype, rather than causing AR down-regulation. Different beta- and alpha-AR subtypes have been characterized in the smooth muscle of equine ileum. The sympathetic relaxation of equine ileum smooth muscle seems to depend mainly on beta(3)-AR subtype activation, with minor involvement of the beta(2) subtype. In the respiratory tract, regional differences have been evidenced in the functionality of beta-AR subtype. The beta(2) subtype predominates in all segments but the beta(2) subtype-mediated adenyl cyclase response is tissue-dependent, with higher activity in tracheal membranes than bronchial or pulmonary ones. Both alpha- and beta-AR subtypes are present in the genital tract of cows. Bovine ovarian and myometrial cell membranes express higher concentrations of beta(2)-ARs than the beta(1) subtype, whereas as far as alpha-ARs are concerned, a single class of alpha(1)-ARs and two distinct classes of alpha(2)-AR binding sites have been discriminated. Interestingly, it has been observed that the activation of the sympathetic system could play an important role in the pathogenesis of bovine ovarian cysts as suggested by the modifications in beta-AR levels in the hypophysis and ovary of cows affected by ovarian cysts. In this species, the phenomenon of down-regulation has been well studied in different organs of veal calves treated with clenbuterol as a "partitioning agent". Since differences exist in AR distribution among species, data obtained in laboratory animals or in human beings cannot be extrapolated to domestic animals and further investigation on AR subtypes in domestic animal tissues is necessary.

Possible role of dexamethasone in sensitizing the beta-2-adrenergic receptor system in vivo in calves during concomitant treatment with clenbuterol

Beta(2)-Agonists blunt the function of the beta-adrenoceptor G-protein adenylate cyclase-signalling system, whereas glucocorticoids reverse the agonist-mediated diminished beta-adrenergic responses; however, these effects have not been reported in vivo in calf lymphocytes. In this study, we first investigated the presence of the beta(2)-adrenergic receptors on calf lymphocytes, and second we tested the effects of either clenbuterol alone or in combination with dexamethasone on receptor expression and function (isoproterenol-induced intracellular adenosine 3',5'-cyclic monophosphate (cAMP) formation) in vivo. (-)-[(125)I]-Iodocyanopindolol (ICYP) binding to intact calf lymphocytes was rapid, saturable (maximal number of binding sites 987 +/- 89 ICYP-binding sites/cell, n = 4) and of high affinity (K(D) value 17.23 +/- 2.8 pmol/l, n = 4). These binding sites were of the beta(2)-subtypes of adrenoceptors as indicated by the fact that beta-agonists inhibited ICYP binding with an order of potency: (-)-isoproterenol > (-)-adrenaline > (-)-noradrenaline. Furthermore, the selective beta(2)-adrenoceptor antagonist ICI 118.551 was about >1,500 times more potent in inhibiting ICYP binding than was the beta(1)-selective adrenoceptor antagonist CGP 20712A. Consequently, calves were treated with clenbuterol (1.0 microg/kg b.i.d., i.v.) for 9 days alone or simultaneously with dexamethasone (0.1 mg/kg, i.v., once a day for 4 days). Clenbuterol decreased the number of lymphocyte beta(2)-adrenergic receptors by about 40-50% after only 48 h of drug administration. This was accompanied by a decrement in isoproterenol-induced lymphocyte cAMP formation. Upon application of both drugs, dexamethasone restored the clenbuterol-mediated decrease in beta(2)-adrenoceptors and cAMP production. Dexamethasone elevated the number of beta(2)-adrenoceptors and cAMP almost 1.5- to 2-fold at 24 h of drug administration, an effect that persisted for up to 24 h following drug withdrawal. Neither clenbuterol nor the combination with dexamethasone had an influence on the affinity of the receptor for the ligand. The present results demonstrate that dexamethasone in vivo upregulates the number and function of calf lymphocyte beta(2)-adrenoceptors, and thus enhances the sensitivity of the beta(2)-adrenoceptor signal-transduction pathway for clenbuterol during concomitant treatment with both drugs.

Road transportation affects blood hormone levels and lymphocyte glucocorticoid and β-adrenergic receptor concentrations in calves

The effect of transportation on blood cortisol and catecholamine levels, lymphocyte glucocorticoid receptor (GR) and beta-adrenergic receptor (beta-AR) concentrations was investigated in calves. Blood samples were collected from 24 six-month-old calves before departure (T(0)), on arrival (T(1)), and at 24 h (T(2)) and one week (T(3)) after arrival. Animals were loaded and transported about 950 km, from the Midy-Pyrenes region (Cahors, France) to the Piedmont region (Italy), over a total of 14 h. Serum cortisol levels and plasma catecholamines (adrenaline, noradrenaline) were determined by radioimmunoassay. Lymphocyte GRs and beta-ARs were measured through binding assays. A significant (P < 0.05) increase in cortisol and catecholamine concentrations was observed immediately after transport. The increase in hormone levels at time T(1) was negatively correlated with lymphocyte GR and beta-AR concentrations. At times T(2) and T(3), blood cortisol and catecholamine levels and lymphocyte GRs and beta-ARs returned to normal. The results demonstrate the activation of the hypothalamic-pituitary-adrenal axis and the catecholaminergic system in long-term transported calves. However, these systems returned to normal within 24 h after the end of transport.

Effect of dietary clenbuterol and cimaterol on muscle composition, beta-adrenergic and androgen receptor concentrations in broiler chickens

Illegal dietary supplementation with beta(2)-agonists has been shown to increase protein deposition and decrease fat accretion in domestic animals. In poultry the metabolic and endocrine responses to beta(2)-agonists are not fully elucidated. In this trial the effects of dietary clenbuterol (1 p.p.m.) and cimaterol (1 p.p.m.) on muscle composition and endocrine response of male broiler chickens were studied. Dietary clenbuterol induced a slight, but in general not significant, improvement of zootechnical performances and carcass yields. Chemical composition of muscle was not influenced by dietary treatments, even if a slight improvement of protein content was observed in treated groups. No effects on fatty acid composition of meat were detected. Both clenbuterol and cimaterol treatments caused a downregulation in testicular androgen receptors and in pulmonary, cardiac and central nervous system beta-adrenergic receptors.

Tissue distribution of clenbuterol in the horse

Plasma and tissue concentrations of clenbuterol (CLB) were determined following oral (p.o.) administration of 1.6 microg/kg twice daily (b.i.d.) for 2 weeks. Horses were administered the last dose on morning of day 15, killed at 0.25, 24, 48, and 72 h post-administration. At 0.25 h, the highest tissue concentrations of CLB were found in the liver (16.21 ng/g), lung (6.48 ng/g), left ventricle (4.99 ng/g), kidney (3.35 ng/g), bronchi (2.56 ng/g), right ventricle (2.08 ng/g), and eye fluids (1.09 ng/g) all of which were higher than that of plasma (1.10 ng/mL). The elimination half-lives (t(1/2k)) for CLB in tissues ranged from 21.2 to 56.3 h, the longest were in the eye fluids (56.9 h), spleen (21.2 h), cerebrum (27.1 h), cerebellum (21.5) and cecum (23.7 h). The t(1/2k) for plasma was 10.9 h. Tissue/plasma ratios of liver (14.7), lung (5.9), left ventricle (4.6), kidney (3.1), bronchi, (2.3) and right ventricle (1.9) were high at 0.25 h and remained elevated up to 72 h. Accumulation and sustained high concentration of CLB relative to plasma in these tissues contributed to the prolonged elimination and the ability to quantify CLB in plasma and urine for a prolonged period.

Stereological study of the adrenal gland of calves treated with clenbuterol

Stereological methods were used to investigate the morphometric variations in the adrenal cell population of calves dosed orally with clenbuterol at an anabolic dose of 20 microg/kg bodyweight per day for 12 weeks. In the treated group the size of the nuclei increased with respect to the control group, and the increases were significant for the maximum linear parameters in all the regions except the zona fasciculata. The largest increases were observed in the epinephrine-producing cells. The quantitative stereological data showed highly significant increases in the nuclear volume fraction, the nuclear surface density and the numerical density in the zona fasciculata of the treated group.

Canine dilated cardiomyopathy: lymphocyte and cardiac alpha(1)- and beta-adrenoceptor concentrations in normal and affected great danes

Serum catecholamine levels and myocardial and lymphocyte adrenergic receptor (AR) concentrations were measured in adult great danes affected by canine dilated cardiomyopathy (DCM) and compared to those of healthy animals. A non-homogeneous population of beta -AR, consisting of beta(1)-AR and beta(2)-AR, was observed in healthy (41 and 59%, respectively) and affected (17 and 83%, respectively) dog lymphocytes. Binding assays revealed that total beta -AR, beta(1)-AR and alpha(1)-AR were significantly downregulated (P<0.05;P<0.01;P<0. 001), both in lymphocyte and myocardial cell membranes of affected dogs. beta(2)-Adrenergic receptor concentrations were significantly reduced only in lymphocyte and right atrium cell membranes (P<0.05). Downregulation was not associated with alterations in receptor binding characteristics, as no significant differences in K(d)values were found. Mean plasma catecholamine levels were significantly higher (P<0.01) in DCM dogs (939+/-41) than in normal subjects (348+/-32), thus suggesting a sympathetic activation. The present study indicates a condition similar to that observed in human patients affected by DCM and that adrenergic receptors in canine lymphocytes reflect the fluctuation of adrenergic receptor concentrations in the myocardium.

Dietary beta-adrenoceptor agonists have a persistent effect on nitric oxide synthesis in rat cultured smooth muscle cells

Several compounds including lipopolysaccharide and sympathomimetics stimulate the expression of the inducible nitric oxide synthase in vascular smooth muscle cells. We evaluated the effect of clenbuterol on nitric oxide (NO) production by vascular smooth muscle cells of the rat aorta in culture. Wistar rats were divided into three diet groups (control, clenbuterol and washout). Aortic vascular smooth muscle cells from rats from these 3 diet groups were cultured in the presence and absence of lipopolysaccharide and/or beta-adrenoceptor agonists. NO release was measured by Griess reagent. Clenbuterol or salbutamol added to cells from control rats potentiated lipopolysaccharide-induced NO release. Cells from rats fed on clenbuterol, in a medium without beta-adrenoceptor agonists, showed a similar potentiation, even after a 10-day washout period. The addition of beta-adrenoceptor agonists to the latter cells did not increase NO production. NG-Nitro-L-arginine decreased nitrite production in lipopolysaccharide-stimulated cells. Our results demonstrate that dietary clenbuterol has a persistent 'ex vivo' effect on lipopolysaccharide-induced NO production by cultured vascular smooth muscle cells.