Physiological and pathological role of the constitutively active α1D adrenoceptors

In previous studies we have shown that in vessels where alpha(1D) adrenoceptors have a functional role, this subtype exhibits constitutive activity, revealed by an increase in contractile tone, cytosolic calcium and inositol phosphate accumulation, in the absence of an agonist. The contraction and the two internal signals were inhibited by prazosin and BMY 7378, a selective alpha(1D) adrenoceptor ligand. This constitutively active population Of alpha(1D) adrenoceptors plays a modulatory role in conductance vessels, preventing abrupt changes in vessel caliber, and consequently, in blood flow, when the stimulus disappears. The lack of this subtype in distributing arteries warrants a quick and fine adjustment of blood flow to adrenergic stimulus. An increased functionality Of alpha(1D) adrenoceptors in aorta, mesenteric and small mesenteric arteries of spontaneously hypertensive adult rats (SHR) has been observed. Consequently, the contractile tone of these vessels remained increased when the adrenergic stimulus disappears as compared with normotensive animals. This change is evidenced only when the hypertensive state appears as it is not observed in prehypertensive (young rats), or captopril-treated adult animals, therefore, it could be directly related to hypertension. (C) 2003 Elsevier Science B.V. All rights reserved.