alpha1-Adrenoceptors in proximal segments of tail arteries from control and reserpinised rats.

It has been recently shown that the supersensitivity of distal segments of the rat tail artery to phenylephrine after chemical sympathectomy with reserpine results from the appearance of alpha(1D)-adrenoceptors. It is known that both alpha(1A)- and alpha(1D)-adrenoceptors are involved in the contractions of proximal portions of the rat tail artery. Therefore, this study investigated whether sympathectomy with reserpine would induce supersensitivity in proximal segments of the rat tail artery, a tissue in which alpha(1D)-adrenoceptors are already functional.

Differential distribution of functional alph}1-adrenergic receptor subtypes along the rat tail artery.

The rat tail artery has been used for the study of vasoconstriction mediated by alpha(1A)-adrenoceptors (ARs). However, rings from proximal segments of the tail artery (within the initial 4 cm, PRTA) were at least 3-fold more sensitive to methoxamine and phenylephrine (n = 6-12; p < 0.05) than rings from distal parts (between the sixth and 10th cm, DRTA).

Differential antagonism by conotoxin rho-TIA of contractions mediated by distinct alpha1-adrenoceptor subtypes in rat vas deferens, spleen and aorta.

The ability of the conotoxin rho-TIA, a 19-amino acid peptide isolated from the marine snail Conus tulipa, to antagonize contractions induced by noradrenaline through activation of alpha1A-adrenoceptors in rat vas deferens, alpha1B-adrenoceptors in rat spleen and alpha1D-adrenoceptors in rat aorta, and to inhibit the binding of [125I]HEAT (2-[[beta-(4-hydroxyphenyl)ethyl]aminomethyl]-1-tetralone) to membranes of human embryonic kidney (HEK) 293 cells expressing each of the recombinant rat alpha1-adrenoceptors was investigated. rho-TIA (100 nM to 1 microM) antagonized the contractions of vas deferens and aorta in response to noradrenaline without affecting maximal effects and with similar potencies (pA2 approximately 7.2, n=4).