Characterization of β‐adrenoceptor mediated smooth muscle relaxation and the detection of mRNA for β1‐, β2‐ and β3‐adrenoceptors in rat ileum

摘要: Functional and molecular approaches were used to characterize the β-AR subtypes mediating relaxation of rat ileal smooth muscle. In functional studies, (−)-isoprenaline was unchanged by CGP20712A (β1-AR antagonist) or ICI118551 (β2-AR but shifted propranolol (pKB=6.69). (±)-Cyanopindolol, {"type":"entrez-protein","attrs":{"text":"CGP12177","term_id":"877152897","term_text":"CGP12177"}}CGP12177 ICID7114 did not cause antagonized relaxation. BRL37344 (β3-AR agonist) caused biphasic relaxation. The high affinity component with low propranolol, (±)-cyanopindolol, tertatolol alprenolol. {"type":"entrez-nucleotide","attrs":{"text":"CL316243","term_id":"44896132","term_text":"CL316243"}}CL316243 unaffected blocked SR58894A antagonist; pA2=7.80). Enhanced after exposure forskolin pertussis toxin showed that β3-AR can be altered manipulation components adenylate cyclase signalling pathway. The β1-AR agonist RO363 relaxed ileum (pEC50=6.18) CGP20712A. Relaxation β2-AR zinterol (pEC50=5.71) ICI118551. In ileum, β1-, β2- mRNA detected. Comparison tissues expression greatest in WAT>colon=ileum>cerebral cortex>soleus; most abundant cerebral cortex>WAT>ileum=colon>soleus; expressed soleus>WAT>ileum=colon>cerebral cortex. These results show β3-ARs are predominant subtype while β1-ARs may produce a small produces through there no evidence for involvement β2-ARs despite detection mRNA. Keywords: β-adrenoceptors, β3-adrenoceptors, gastrointestinal muscle, relaxation, messenger RNA Introduction Although intestinal originally described as (Lands et al., 1967) atypically affinities antagonists propranolol-resistant responses observed muscle preparations from several species indicated other involved these (see Arch & Kaumann, 1993, review). Atypical resistant blockade selectively stimulated novel group agonists also adipocytes. subsequently cloned sequenced (Emorine 1989) found share many pharmacological characteristics atypical β-AR. highly adipose tissue such BRL 37344, SR 58611A CL 316,243 potent stimulants lipolysis thermogenesis, marked weight loss obese animals, increase insulin sensitivity improve glucose tolerance diabetic animals. Whilst human is emerging an exciting target development selective potential treatments obesity diabetes (Strosberg Pietri-Rouxel, 1996), same compounds useful treatment irritable bowel syndrome. regions tract colon, stomach including (Berkowitz 1995; Evans 1996; Roberts 1997). mediated β1- CGP 20712A ICI 118551 (for review see Manara 1995). Earlier studies non-selective various animal models. For example, using models have shown reduction responsiveness intestine (Ozturk 1996). Decreased salbutamol particular note potency strongly suggests it acting rather than β2-ARs. In addition, recent binding study mapping throughout concentration radioligand [125I]-CYP (20 pM) so would label only 1.5% each sample (Yu Ouyang, findings therefore offer limited information on changes density tools/compounds appropriate examination all three subtypes. It necessary clearly establish role contribution now available, more comprehensive possible. A agonist, CL 316243, has been developed at least 10,000 fold selectivity compared respectively (Dolan 1994). More recently first new tools enabled clear demonstration colon brown (Manara 1996). Previous carried out presence relative examined Studies (Growcott 1993; Hoey 1996) stimulation response blockade. aim this utilize well present assess muscle. We measured levels