Abstract
The responsiveness to sympathomimetic amines of the isolated myocardium and the changes in cardiac beta-adrenocepters in DOCA-salt hypertensive rats were examined. The male Wistar rats were nephrectomized unilaterally, and D0CA(6 mg/animal/ week) and 1 % NaCl solution were given for 2 weeks(2w-DS-rat), 6 weeks(6w-DS-rat) or 10 weeks(10w-DS-rat). The papillary muscle of left ventricle and left atrium were isolated, and the isometric contractions were recorded. The changes in adrenoceptors were examined using the technique of radioligand binding assay. The responsiveness to isoproterenol(Iso) decreased in 6w- and 10w-DS-rats as compared to control rats, but did not in 2w-DS-rats. The responsiveness to phenylephrine (Phe) in the presence of propranolol also decreased in 6w-DS-rats. When the reponsiveness was represented in terms of % of the maximal réponse to Ca++, the decrease in the responsiveness to Iso were remarkable, but the responsiveness to Phe in the presence of propanolol did not change. The number of beta-adrenoceptors decreased in 6w-DS-rats by about 20 %. It is probable that the changes in the reponsiveness to Iso are due to the changes in adrenoceptors as well as some steps beyond adrenoceptors, and the changes in the responsiveness to Phe in the presence of propranolol are mainly due to changes in steps beyond adrenoceptors.
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