Time Course Alterations in Vascular Adrenergic Responsiveness in the DOCA/NaCl-Treated Rat

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Abstract
Rats treated with deoxycorticosterone acetate and sodium chloride (DOCA/NaCl) developed a time-dependent increase in blood pressure which was associated with a reduced in vitro .beta.- and an elevated .alpha.-adrenergic responsiveness. Isoproterenol-induced relaxation of aortic smooth muscle from the DOCA-NaCl-treated rats was similar to controls 1 wk after treatment, was significantly attenuated as the blood pressure began to rise (wk 4) and was completely abolished when the blood pressure exceeded 150 mm Hg (wk 12). The aortic smooth muscle sensitivity to norepinephrine was significantly increased prior to (wk 1), during the rise (wk 4) and during the maintenance of an elevated systolic blood pressure (> 150 mm Hg; wk 12). No significant differences were observed between the 2 groups in either the contractile response of the aortic ring preparations to KCl or in the relaxation properties in response to sodium nitrite. Alterations in both the .alpha.- and .beta.-adrenergic responsiveness evidently occur in the DOCA/NaCl-treated animal. The enhancement of the .alpha.-adrenergic responsiveness occurs prior to any change in blood pressure, while the attenuated .beta.-adrenergic responsiveness parallels the elevation in blood pressure, suggesting that these reciprocal alterations of adrenergic responsiveness may be responsible for the eventual development of hypertension induced with DOCA/NaCl treatment in rats.