Erowid References Database
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Larsson B.
“Demonstration of alpha-Adrenoceptors in the Rabbit Bladder Base and Urethra with 3H-Dihydroergocryptine Ligand Binding”.
Acta pharmacol et toxicol. 1983;52(3):188-194.
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Abstract
The purpose of this work was to demonstrate the presence of alpha-adrenoceptors in a crude membrane preparation made from rabbit bladder base and urethra. This was achieved by radioligand binding studies, using 3H-dihydro-e-ergocryptine (3H-DHE) as the radioligand. The specific binding, i.e. the binding that could be inhibited by 10-5 M phentolamine was saturable with 73 fmol 3H-DHE bound per mg membrane protein. Binding was at steady state after 60 min., and reversible. Rate constants for association and dissociation were- 3X 10-7 M -1min and 2 X 10-2 min-1.. respectively. A number of compounds were tested for their abilities to compete with 3H-DHE for the binding sites. The relative afinity of some adrenoceptor agonists was: ( - )- adrenaline > (-)-noradrenaline >> (+/-)-isoprenaline. Stereoselectivity was shown since (-)-noradrenaline had 42 times higher affinity than (+)-noraderenaline. Adrenoceptor antagonists inhibited 3H-DHE bindings in the following order of potency:.DHE>phentolamine>> (+/-)-propranolol.. The dissociation constant, KD for DHE to the binding sites was estimated in three different ways. The constants were derived from saturation, competition, and kinetic studies, and gave KD values of 1.1, 1.4 and 0.7 nM, respectively. The results suggest that alpha-adrenoceptors were labelled by 3H-DHE in the tissue homogenates.
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