<Originals>Characterization of dopamine-induced vasorelaxation in isolated renal arteries from stroke-prone spontaneously hypertensive rats

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The dopamine (DA)-induced relaxation in ring preparations of main renal arteries (MRA) and intrarenal arteries (IRA) from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY) was pharmacologically investigated in animals at 1.5,3 and 6 months of age. DA elicited endothelium-independent relaxation in MRA and IRA pretreated with phenoxybenzamine from SHRSP and WKY at 1.5 months of age, and the relaxant responses in both arteries were significantly greater in SHRSP than in WKY. The DA-induced relaxations in MRA SHRSP and WKY were almost negligible at 3 months of age and were not found at 6 months of age. In IRA, the DA-induced relaxation was age-dependently attenuated in SHRSP and WKY, and the degree of attenuation was greater in WKY than in SHRSP. The DA-induced relaxations in MRA and IRA from WKY and SHRSP were inhibited by SCH 23390,a DA_1 receptor antagonist, but not by sulpride, a DA_2 receptor antagonist. The relaxations produced by SKF 38393,a DA_1 receptor agonist, in MRA and IRA were greater in SHRSP at 1.5 months of age than in age-matched WKY. In addition, the pattern of age-related alterations in relaxations produced by SKF 38393 was similar to that produced by DA. Bromocriptine, a DA_2 receptor agonist, did not elicit relaxation in MRA and IRA from either group. There were no significant differences in relaxation in response to the cyclic AMP-generating system affecting drugs (forskolin, dibutyryl cyclic AMP and 3-isobutyl-1-methyxanthine) between SHRSP and age-matched WKY in MRA and IRA at any age tested, and the responses to these drugs in MRA and IRA were not affected by ageing in either group. In conclusion, the DA_1-receptor mediated vasorelaxation in renal arteries is greater in SHRSP than in WKY. In addition, there are regional and strain differences in the degree of attenuation of the DA_1 receptors mediating relaxation in association with increasing age. Thus, the enhanced DA_1 receptor-mediated response in renal arteries from SHRSP may be a compensatory mechanism for the increased renal vascular resistance and reactivities associated with hypertension. Furthermore, the alterations of DA_1 receptor-mediated relaxant responses in renal arteries from WKY and SHRSP may be associated with the change in the number of receptors or their coupling to adenylate cyclase, rather than a post-receptor event in the adenylate cyclase/cyclic AMP pathway.
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<Originals>Characterization of dopamine-induced vasorelaxation in isolated renal arteries from stroke-prone spontaneously hypertensive rats

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