<Originals>The responses to various relaxing substances in the renal arteries and the aortas of stroke-prone spontaneously hypertensive rats (SHRSP) at various ages

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Recent studies have indicated that the reduced relaxation responses to acetylcholine (ACH) in adult and old SHRSP blood vessels might be due to the release of endothelium-derived contracting factor (EDCF) without the reduced release of endothelium-derived relaxing factor (EDRF), which may be a cause of hypertension in SHR or SHRSP. But those studies have carried out in the large vessels. We studied the relaxation responses to various substances including EDRF releasing substances in the renal arteries of SHRSP and WKY at 1.5,3 and 6 months of age. The responses to ACH and histamine decreased with age in the renal arteries and the aortas of both strains, being more remarkable in SHRSP than in WKY. In the renal artery, ACH at high doses under the contraction produced the relaxation followed by the contraction in the 6-month-old WKY and SHRSP, being more greater in WKY than in SHRSP. N^G-nitro-L-arginine and indomethacin abolished the relaxation and the contraction in both strain, respectively. In the quiescent renal artery, ACH produced only the contraction in the 6-month-old SHRSP and WKY, being greater in WKY than in SHRSP. Indomethacin abolished the contraction and N^G-nitro-L-arginine enhanced the contraction in both strains, respectively. In the quiescent aorta, ACH did not produce the contraction in either strain. Histamine did not produce the contraction in the quiescent renal arteries and aortas in the 6-month-old SHRSP and WKY. The responses to nitroglycerin in the renal arteries and the aortas of SHRSP and WKY did not change with age. The responses to isoproterenol decreased with age in the renal arteries and aortas of SHRSP and WKY, being more remarkable in SHRSP than in WKY. The remarkable reduced responses to isoproterenol were observed in the both arteries of SHRSP at 3 and 6 months of age compared with those in the age-matched WKY. The responses to forskolin and isobutylmethyl xanthine slightly decreased with age in both arteries of SHRSP, but not in WKY. The responses to dibutyryl cyclic monophosphate did not decrease with age in the renal arteries and the aortas of both strains. Dopamine produced the relaxation only in the young SHRSP and WKY. The responses were not different with the strain. The responses to diltiazem in the renal artery and the aorta did not differ with the strain. These results suggest that endothelium-dependent relaxations in the renal artery and the aorta are mediated by nitric oxide, and in the old SHRSP blood vessels, those relaxation are impaired by interfering with the release and/or action of EDRF. ACH releases EDCF in addition to EDRF in the renal arteries of old SHRSP and WKY, but not in the aorta. The reduced responses to EDRF releasing substances contribute to the maintenance of hypertension of SHRSP, but are not cause of hypertension. The reduced responses to β-adrenoceptor stimulating substance contribute to the development and the maintenance of hypertension of SHRSP. Dopamine plays a role in controlling the renal circulation in young rats and has no role as to the onset of hypertension.
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<Originals>The responses to various relaxing substances in the renal arteries and the aortas of stroke-prone spontaneously hypertensive rats (SHRSP) at various ages

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