Functional involvement of alpha 1- and alpha 2-adrenoceptors in 86Rb efflux from liver slices and lipolysis in guinea-pig isolated adipocytes.
1. The application of an alpha 1-adrenoceptor agonist, amidephrine, to guinea-pig liver slices increases glucose release and 86Rb efflux. Since prazosin was more potent than yohimbine in inhibiting both responses, alpha 1-adrenoceptors seem to be involved in the effects evoked by the agonist. 2. Clonidine (an alpha 2-adrenoceptor agonist) at doses unable to activate liver glycogenolysis increased 86Rb release and potentiated isoprenaline in promoting 86Rb efflux. Since yohimbine antagonized clonidine in promoting 86Rb efflux, alpha 2-adrenoceptors also seem to control plasmalemmal permeability to 86Rb. 3. The liver slice responses resulting from alpha 1- and alpha 2-adrenoceptor stimulation required extracellular calcium. Calcium absence or the administration of D-600 attenuated the effects of amidephrine on glucose release and 86Rb outflow and Ca2+ excess re-established both responses. D-600 and apamin blocked clonidine-induced 86Rb efflux, suggesting that alpha 2-adrenoceptor stimulation activates calcium dependent K+ channels. 4. alpha 2-adrenoceptors do not appear to mediate antilipolytic effects in guinea-pig fat cells.
Department of Pharmacology, School of Medicine, University of Salamanca, Spain.
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Maroto
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Moratinos
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Sancho
D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology; D004837:Epinephrine / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000502:physiology*; D008099:Liver / Q000378:metabolism*; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D012414:Rubidium Radioisotopes
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D008112:Liver Glycogen; D011942:Receptors, Adrenergic, alpha; D012414:Rubidium Radioisotopes; D005947:Glucose; D007545:Isoproterenol; D002118:Calcium; D004837:Epinephrine