Studies on Isoproterenol Stimulation of Adenyl Cyclase in Membrane Preparations from the Bovine Thyroid

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Abstract
Catecholamine stimulation of adenyl cyclase activity associated with bovine subcellular fractions enriched in plasma membranes is described. The relative potencies of isoproterenol (IPNA), epinephrine (E), and norepinephrine (NE) were 4.7:1.0:0.02, which is characteristic for a beta-adrenergic receptor system. Stimulation with IPNA (5 times 10- minus 6 M) was inhibited by propranolol. The inhibition was stereospecific for the L-isomer of propranolol and a concentration as low as 2 times 10- minus 8 M was required to effect 50% inhibition. Both these observations, and the competitive kinetics of inhibition which applied to the system, confirmed the classification of a beta-adrenergic receptor system. Phentolamine, an alpha-antagonist, also inhibited IPNA stimulation, although high doses (5 times 10- minus M) were required to cause total inhibition. Inhibition was also observed with quinidine (1 mM) and lignocaine (10- minus 2 M).

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