Relationship between lipolysis and cyclic AMP generation mediated by atypical beta-adrenoceptors in rat adipocytes.
1. The nature of the beta-adrenoceptor(s) mediating adenylyl cyclase activation in rat adipocyte ghosts by (-)-isoprenaline and the lipolytically selective beta-adrenoceptor agonist, BRL 37344, was investigated by use of the beta 1-selective antagonist, CGP 20712A. The results were compared with lipolysis in adipocytes. 2. While in lipolysis BRL 37344 was a full and 10 times more potent agonist than (-)-isoprenaline, in adenylyl cyclase activation similar pD2 values for both agonists were found. BRL 37344 was only a partial agonist on rat adipocyte adenylyl cyclase, with an intrinsic activity of 0.62. 3. With CGP 20712A small rightward shifts of the (-)-isoprenaline concentration-response curve (CRC) were observed at concentrations up to 10 microM, while at 100 microM and 1 mM clear rightward shifts occurred. The BRL 37344 CRC was not shifted with antagonist concentrations up to 10 microM. Only at 100 microM and 1 mM CGP 20712A were rightward shifts observed. 4. CGP 20712A concentrations of 10 microM and 100 microM depressed the maximum of the (-)-isoprenaline CRC to 89 and 60%, while the BRL 37344 CRCs retained the control maximum effect (62% of (-)-isoprenaline). Only at 1 mM CGP 20712A, was the CRC of BRL 37344 depressed, while the (-)-isoprenaline maximum was diminished further. 5. It was concluded that as with lipolysis, (-)-isoprenaline acts both through typical beta 1- and atypical beta 3-adrenoceptors for activation of adenylyl cyclase, while BRL 37344 acts solely through atypical beta 3-adrenoceptors. 6. The results also demonstrate that the relationship between adenosine 3':5'-cyclic monophosphate (cyclic AMP) and lipolysis is different for BRL 37344 and (-)-isoprenaline. Although the maximum activation of adenylyl cyclase by BRL 37344 is only 62% of that by (-)-isoprenaline, the distance between the lipolysis and adenylyl cyclase CRCs is much larger in the case of BRL 37344, indicating a larger transduction reserve for this agonist.
Department of Pharmacology and Therapeutics, University of Groningen, The Netherlands.
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Hollenga
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Brouwer
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Zaagsma
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000096:biosynthesis*; D004983:Ethanolamines / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000502:physiology*
D004983:Ethanolamines; D007093:Imidazoles; D011943:Receptors, Adrenergic, beta; C057368:BRL 37344; C049763:CGP 20712A; D000242:Cyclic AMP; D007545:Isoproterenol