Hypoaminoacidemia caused by imipramine but not by clenbuterol is dissociable from hyperglycemia and hyperinsulinemia

Intracellular β2-adrenergic receptor signaling specificity in mouse skeletal muscle in response to single-dose β2-agonist clenbuterol treatment and acute exercise

The aim of this study was to clarify the intracellular β₂-adrenergic receptor signaling specificity in mouse slow-twitch soleus and fast-twitch tibialis anterior (TA) muscles, resulting from single-dose β₂-agonist clenbuterol treatment and acute exercise. At 1, 4, and 24 h after single-dose treatment with clenbuterol or after acute running exercise, the soleus and TA muscles were isolated and subjected to analysis. The phosphorylation of p38 mitogen-activated protein kinase (MAPK) increased after single-dose clenbuterol treatment and acute exercise in the soleus muscle but not in the TA muscle. Although there was no change in the phosphorylation of Akt after acute exercise in either muscle, phosphorylation of Akt in the soleus muscle increased after single-dose clenbuterol treatment, whereas that in the TA muscle remained unchanged. These results suggest that p38 MAPK and Akt pathways play a functional role in the adaptation to clenbuterol treatment and exercise, particularly in slow-twitch muscles.

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.