Selective Agonist Clenbuterol Research Articles

A Quantitative Analysis of mRNA Expression of α1 and β-adrenoceptor Subtypes and Their Functional Roles in Human Normal and Obstructed Bladders

We compared the expression level of alpha 1-adrenoceptor (AR) subtype mRNA to that of beta-AR subtype mRNA in control and obstructed human bladders, and examined whether alpha 1-AR mediated contraction and beta-AR mediated relaxation of human detrusor muscle are altered by bladder outlet obstruction. A real-time quantitative reverse transcriptase-polymerase chain reaction based method was used to quantify alpha1 and beta-AR subtype mRNA expression. The contractile response to alpha-AR agonists and the relaxant effect of beta-AR agonists were examined using an isometric contraction technique. The mRNA of alpha 1a, alpha 1b, alpha 1d, beta 1 and beta 2-AR mRNAs was expressed at low levels, while beta 3-AR was the most highly expressed subtype at the mRNA level in control and obstructed bladders. The expression level of alpha 1 and beta-AR subtype mRNA was not significantly different between the 2 groups. The mean contractile response to 10(-4) M phenylephrine +/- SEM was only 4.4% +/- 1.4% and 5.2% +/- 1.4% of the 10(-7) M carbachol induced contraction in the control and obstructed groups, respectively. Contractile responses to phenylephrine were not significantly increased in obstructed bladder. Isoproterenol and the beta 3-AR selective agonist L755,507 relaxed human detrusor muscle in a concentration dependent manner (10(-9) to 10(-4) M). However, the beta 1/beta 2-AR agonist dobutamine and the beta 2-AR selective agonist clenbuterol did not produce relaxation at a concentration of 10(-9) to 10(-5) M in the 2 groups. These findings indicate that neither up-regulation of alpha1-ARs nor down-regulation of beta-ARs occurs and relaxation mediating beta 3-ARs are by far predominant in the human obstructed bladder. Therefore, it is not likely that bladder alpha1-ARs are responsible for detrusor overactivity and storage symptoms in patients with benign prostatic obstruction.

Activation of beta2- and beta3-adrenergic receptors increases brain tryptophan.

Brain tryptophan concentrations are increased by various stressful treatments, an effect that can be prevented by beta-adrenoceptor antagonists. This study aimed to determine the beta-adrenergic subtype responsible for the tryptophan response. Male CD-1 mice received intraperitoneal injections of nonselective and subtype-selective beta-adrenergic antagonists 20 min before subtype-selective beta-agonists. Selected brain regions were dissected for analysis of tryptophan content by high-performance liquid chromatography with electrochemical detection. The beta(2)-selective agonist clenbuterol (0.3 mg/kg) induced increases in brain tryptophan that reached a peak ( approximately 60%) 1 h following injection and small but statistically significant increases ( approximately 20%) in 5-hydroxyindoleacetic acid: serotonin ratios 2 h following injection. The beta(1)-selective agonist dobutamine (10 mg/kg) produced less robust increases ( approximately 40%) in brain tryptophan, whereas the beta(3)-selective agonists BRL 37344 (0.2 mg/kg (+/-)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl] phenoxy]acetic acid sodium)) and CL 316243 [0.1 mg/kg disodium 5-[(2R)-2-([(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate)] resulted in larger increases (80 to 100%). Pretreatment with the beta(2)-selective antagonist ICI 118551 (0.5 mg/kg (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[(1-methylethyl)amino]-2-butanol) attenuated the increases in tryptophan induced by both clenbuterol (0.1 mg/kg) and dobutamine (10 mg/kg). Pretreatment with the beta(1/2)-selective antagonist propranolol (2.5 mg/kg), the beta(3)-selective antagonist SR 59230A [1.5, 2.5, 5, or 20 mg/kg (3-(2-ethylphenoxy)-1[1S)-1,2,3,4-tertahydronaphth-1-yl-amino]-(2S)-2-propanol oxalate)], or ICI 118551 (0.5 mg/kg) did not prevent the BRL 37344-induced increase in brain tryptophan, whereas the beta(1/2/3)-antagonist bupranolol (10 mg/kg) attenuated it. CL 316243 had no effect on brain tryptophan in beta(3)-receptor knockout mice, whereas clenbuterol increased brain tryptophan, indicating that beta-adrenergic modulation of brain tryptophan occurs in the absence of beta(3)-receptors. We conclude that activation of either beta(2)- or beta(3)-adrenergic receptors, but not beta(1)-adrenergic receptors, increases mouse brain tryptophan content.

Increase in skeletal muscle protein content by the beta-2 selective adrenergic agonist clenbuterol exacerbates hypoalbuminemia in rats fed a low-protein diet.

This investigation examined how the nutritional status of rats fed a low-protein diet was affected when the animals were treated with the beta-2 selective agonist clenbuterol (CL). Males (4 weeks old) from an inbred, specific-pathogen-free strain of hooded rats maintained at the Dunn Nutritional Laboratory were used in the experiments (N = 6 rats per group). CL treatment (Ventipulmin, Boehringer-Ingelheim Ltd., 3.2 mg/kg diet for 2 weeks) caused an exacerbation of the symptoms associated with protein deficiency in rats. Plasma albumin concentrations, already low in rats fed a low-protein diet (group A), were further reduced in CL rats (A = 25.05 +/- 0.31 vs CL = 23.64 +/- 0.30 g/l, P < 0.05). Total liver protein decreased below the level seen in either pair-fed animals (group P) or animals with free access to the low-protein diet (A = 736.56 +/- 26 vs CL = 535.41 +/- 54 mg, P < 0.05), whereas gastrocnemius muscle protein was higher than the values normally described for control (C) animals (C = 210.88 +/- 3.2 vs CL = 227.14 +/- 1.7 mg/g, P < 0.05). Clenbuterol-treated rats also showed a reduction in growth when compared to P rats (P = 3.2 +/- 1.1 vs CL = -10.2 +/- 1.9 g, P < 0.05). This was associated with a marked decrease in fat stores (P = 5.35 +/- 0.81 vs CL = 2.02 +/- 0.16 g, P < 0.05). Brown adipose tissue (BAT) cytochrome oxidase activity, although slightly lower than in P rats (P = 469.96 +/- 16.20 vs CL = 414.48 +/- 11.32 U/BAT x kg body weight, P < 0.05), was still much higher than in control rats (C = 159.55 +/- 11.54 vs CL = 414.48 +/- 11.32 U/BAT x kg body weight, P < 0.05). The present findings support the hypothesis that an increased muscle protein content due to clenbuterol stimulation worsened amino acid availability to the liver and further reduced albumin synthesis causing exacerbation of hypoalbuminemia in rats fed a low-protein diet.