Article date: November 1989
By: Anton D. Michel, Dana N. Loury, Roger L. Whiting in Volume 98, Issue 3, pages 883-889
The α1‐adrenoceptors present in membranes of rat liver, cortex and submaxillary gland were labelled with [3H]‐prazosin and the affinity of 15 ligands for these receptors was determined.
In saturation studies, [3H]‐prazosin bound with high affinity (Kd = 30–39 pM) to a single population of sites in all three preparations.
In competition studies using rat cortex, evidence for heterogeneity of the α1‐adrenoceptor binding sites was obtained. Displacement isotherms for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 were biphasic and were consistent with the presence of both α1A‐ and α1B‐adrenoceptor subtypes as described by Morrow & Creese (1986) and Han et al. (1987).
The rat liver and submaxillary gland membrane preparations both possessed homogeneous populations of α1‐adrenoceptors. However, there were pharmacological differences between the receptors in these two preparations. Rat submaxillary gland α1‐adrenoceptors displayed high affinity for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 and therefore appeared to represent α1A‐adrenoceptors. Rat liver α1‐adrenoceptors possessed lower affinity for these ligands (6–65 fold) suggesting that these receptors were of the α1B‐subtype.
Spiperone exhibited 12.9 fold higher affinity for rat liver α1B‐adrenoceptors than for rat submaxillary gland α1A‐adrenoceptor and may therefore represent the first α1B‐adrenoceptor selective ligand.
The α1‐adrenoceptors present in membranes of rat liver, cortex and submaxillary gland were labelled with [3H]‐prazosin and the affinity of 15 ligands for these receptors was determined.
In saturation studies, [3H]‐prazosin bound with high affinity (Kd = 30–39 pM) to a single population of sites in all three preparations.
In competition studies using rat cortex, evidence for heterogeneity of the α1‐adrenoceptor binding sites was obtained. Displacement isotherms for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 were biphasic and were consistent with the presence of both α1A‐ and α1B‐adrenoceptor subtypes as described by Morrow & Creese (1986) and Han et al. (1987).
The rat liver and submaxillary gland membrane preparations both possessed homogeneous populations of α1‐adrenoceptors. However, there were pharmacological differences between the receptors in these two preparations. Rat submaxillary gland α1‐adrenoceptors displayed high affinity for amidephrine, benoxathian, oxymetazoline, phentolamine and WB 4101 and therefore appeared to represent α1A‐adrenoceptors. Rat liver α1‐adrenoceptors possessed lower affinity for these ligands (6–65 fold) suggesting that these receptors were of the α1B‐subtype.
Spiperone exhibited 12.9 fold higher affinity for rat liver α1B‐adrenoceptors than for rat submaxillary gland α1A‐adrenoceptor and may therefore represent the first α1B‐adrenoceptor selective ligand.
DOI: 10.1111/j.1476-5381.1989.tb14617.x
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