Abstract
After depletion of intracellular calcium stores sensitive to noradrenaline, a spontaneous increase in the resting tone (IRT) when incubated in Ca2+-containing solution was observed in isolated rat aorta, but not in tail artery. This IRT does not depend on agonist activation of α1-adrenoceptors but it is inhibited by prazosin. A close relationship was found between the inhibitory potencies of prazosin (pIC50 = 9.833), BMY 7378 (pIC50 = 8.924), and 5-methylurapidil (pIC50 = 7.883) against IRT and their affinities for cloned α1D-adrenoceptors. Chloroethylclonidine (100 μmol · l−1) did not inhibit the IRT. After depletion of internal calcium stores by noradrenaline in absence of the agonist, loading in Ca2+-containing solution also brings about an increase in the inositol phosphate (IP) levels in rat aorta (not seen in tail artery) that is inhibited by prazosin (1 μmol · l−1), BMY 7378 (10 μmol · l−1), and 5-methylurapidil (10 μmol · l−1), thus confirming the results obtained in contractile studies. Chloroethylclonidine (100 μmol · l−1) did not inhibit this IP accumulation. The fact that the IRT and the IP accumulation related to it can be selectively inhibited by different α1-adrenoceptor antagonists suggests the existence of a population of α1D-adrenoceptors that show constitutive activity in rat aorta, not in tail artery.
Footnotes
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Send reprint requests to: Pilar D'Ocon, Departamento de Farmacologı́a, Facultad de Farmacia, Universitat de València, Avda Vicent Andres estelles s/n 46100 Burjassot, València, Spain. E-mail: m.pilar.docon{at}uv.es
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↵1 This work was supported by a research grant from the Spanish Comisión Interministerial de Ciencia y Tecnologı́a (SAF98-0123).
- Abbreviations:
- IRT
- increase in the resting tone
- IP
- inositol phosphate
- NA
- noradrenaline
- W
- washing
- A
- antagonist
- Received April 4, 2000.
- Accepted August 1, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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