Determination of alpha 1-adrenoceptor subtype selectivity by [3H]-prazosin displacement studies in guinea-pig cerebral cortex and rat spleen membranes.
1. [3H]-prazosin homogeneously labels alpha 1-adrenoceptors in guinea-pig cerebral cortex and rat spleen membranes with dissociation constants of 1.28 and 1.49 x 10(-10) M respectively. 2. Phentolamine and WB 4101 displacement studies show that guinea-pig cerebral cortex contains 30% alpha 1A- and 70% alpha 1B-adrenoceptor subtypes, whereas rat spleen contains a virtually homogeneous alpha 1B-adrenoceptor subtype population. The alpha 1-adrenoceptor population of rat thoracic aorta is predominantly of the alpha 1A-adrenoceptor subtype, and in guinea-pig thoracic aorta it is mainly of the alpha 1B-adrenoceptor subtype. 3. Half of the compounds displacing [3H]-prazosin bound to guinea-pig cerebral cortex membranes display alpha 1A-adrenoceptor selectivity. Among these compounds, WB 4101 and methoxamine are most selective, displaying selectivity ratios of approximately 38 and approximately 26 respectively. 4. The affinity constants of the non-selective compounds for the alpha 1-adrenoceptor in guinea-pig cerebral cortex membranes correlate well with the affinity constants obtained for alpha 1B-adrenoceptors in rat spleen membranes. The affinities of selective compounds for the alpha 1B-adrenoceptor subtype in guinea-pig cerebral cortex correlate very well with their affinity for alpha 1B-adrenoceptor in the rat spleen homogenate. Both regression lines coincide with the line of identity. The affinity constants of selective compounds for the alpha 1A-adrenoceptors in guinea-pig cerebral cortex only apparently correlate with the affinity for either the alpha 1B-adrenoceptors in guinea-pig cerebral cortex or in the rat spleen.(ABSTRACT TRUNCATED AT 250 WORDS)[1]References
- Determination of alpha 1-adrenoceptor subtype selectivity by [3H]-prazosin displacement studies in guinea-pig cerebral cortex and rat spleen membranes. Veenstra, D.M., van Buuren, K.J., Nijkamp, F.P. Br. J. Pharmacol. (1992) [Pubmed]
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