A Differential Alteration in the Responsiveness of Isolated Cardiac Muscles to Alpha-and Beta-adrenergic Agonists in DOCA-Salt Hypertensive Rats

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We examined the alteration of the responsiveness to adrenergic agonists and changes in the density of adrenoreceptors in the hearts of rats with deoxycorticosterone acetate (DOCA)-salt hypertension in order to determine the relationship between changes in adrenoreceptor responsiveness and adrenoreceptor density in this hypertension model. The maximal increase in the tension development with phenylephrine in the presence of propranolol and with isoproterenol decreased to a larger extent in the latter, but the PD_2 values for these agonists did not change. Decreases in maximal tension development with phenylephrine and Ca^<2+> were similar. The density of alpha-and betaadrenoceptors decreased similarly. In conclusion, whereas a decreased adrenoreceptor density may not significantly contribute to a decreased agonist responsiveness in DOCA-salt hypertensive rats, altered Ca^<2+> sensitivity contributes to the observed reduction in agonist responsiveness.
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