Abstract
We have used the α1D-adrenoceptor selective antagonist, BMY 7378, the α1D-selective agonists, adrenaline and phenylephrine, the α1A-selective antagonists, (+)-niguldipine, SB 216469 and WB4101, and the non-subtype-selective α1-adrenoceptor antagonist, nemonapride, to investigate the presence of α1D-adrenoceptors in rat tissues at the protein level. Radioligand binding studies using [3H]prazosin as the radioligand were performed in three tissues containing α1D-adrenoceptor mRNA, spleen, cerebral cortex and kidney, and in comparison in one tissue not containing α1D-adrenoceptor mRNA, liver. Cerebral cortex and kidney were also studied upon α1B-adrenoceptor inactivation by chloroethylclonidine treatment (10 μM, 30 min, 37°C). Experiments with cloned rat α1-adrenoceptor subtypes transiently expressed in COS cells confirmed the known selectivity of the investigated drugs for α1-adrenoceptor subtypes or the lack thereof of nemonapride. Accordingly nemonapride had steep and monophasic competition curves in all native and chloroethylclonidine-treated tissues. BMY 7378 also had steep and monophasic competition curves and low affinity in all native tissues. In contrast, adrenaline and phenylephrine (in the presence of 100 μM GTP) had monophasic competition curves of low affinity in liver and spleen but biphasic competition curves in cerebral cortex and kidney. Following chloroethylclonidine treatment competition curves for adrenaline, phenylephrine, (+)-niguldipine, SB 216469 and WB 4101 remained biphasic in cerebral cortex and kidney while those for nemonapride remained monophasic. We conclude that α1D-adrenoceptors are not readily detectable at the protein level in a variety of rat tissues where their mRNA is expressed. The biphasic competition curves of some agonists and antagonists in chloroethyl-clonidine-treated rat tissues do not represent α1D-adrenoceptors and are not readily explained by the present α1A/α1B/α1D-adrenoceptor classification.
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Received: 11 December 1996 / Accepted: 22 January 1997
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Yang, M., Verfürth, F., Büscher, R. et al. Is α1D-adrenoreptor protein detactable in rat tissues?. Naunyn-Schmiedeberg's Arch Pharmacol 355, 438–446 (1997). https://doi.org/10.1007/PL00004966
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DOI: https://doi.org/10.1007/PL00004966