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α 2 - and β-adrenoceptors (AR) reciprocally control catecholamine release and vascular tension. Disorders in these functions are present in spontaneously hypertensive rats (SHR). The present study tested if α 2 AR dysfunctions resulted from altered α 2 AR/βAR interaction. Blood pressure (BP) was recorded through a femoral artery catheter and cardiac output by an ascending aorta flow probe. Total peripheral vascular resistance (TPR) was calculated. Norepinephrine release was stimulated by a 15-min tyramine-infusion, which allows presynaptic release-control to be reflected as differences in overflow to plasma. Surgical stress activated some secretion of epinephrine. L-659,066 (α 2 AR-antagonist) enhanced norepinephrine overflow in normotensive controls (WKY) but not SHR. Nadolol (β 1+2 ) and ICI-118551 (β 2 ), but not atenolol (β 1 ) or SR59230A [β (3)/1 L  ] prevented this increase. All βAR antagonists allowed L-659,066 to augment tyramine-induced norepinephrine overflow in SHR and epinephrine secretion in both strains. Inhibition of cAMP-degradation with milrinone and β 3 AR agonist (BRL37344) enhanced the effect of L-659,066 on release of both catecholamines in SHR and epinephrine in WKY. β 1/2 AR antagonists and BRL37344 opposed the L-659,066-dependent elimination of the TPR-response to tyramine in WKY. α 2 AR/βAR antagonists had little influence on the TPR-response in SHR. Milrinone potentiated the L-659,066-dependent reduction of the TPR-response to tyramine. Conclusions: β 2 AR activity was a required substrate for α 2 AR auto inhibition of norepinephrine release in WKY. β 1+2 AR opposed α 2 AR inhibition of norepinephrine release in SHR and epinephrine secretion in both strains. βAR-α 2 AR reciprocal control of vascular tension was absent in SHR. Selective agonist provoked β 3 AR-G i  signaling and influenced the tyramine-induced TPR-response in WKY and catecholamine release in SHR.

Altered β1−3-adrenoceptor influence on α2-adrenoceptor-mediated control of catecholamine release and vascular tension in hypertensive rats