Characterization of alpha-adrenoceptors on isolated rabbit renal arterioles

Postsynaptic alpha-adrenoceptors were characterized in afferent and efferent arterioles isolated from rabbit renal cortex. In both the afferent and efferent arteriole the selective alpha 1-adrenoceptor agonists phenylephrine and cirazoline produced concentration-dependent vasoconstrictor responses with the maximum responses being equal to that of norepinephrine. The selective alpha 2-receptor agonists B-HT 933 and UK 14304 were examined over a concentration range of 10(-9) to 10(-4) M. At these concentrations, they were either inactive (B-HT 933) or produced maximum contractile responses only 60% (UK 14304) of that produced by norepinephrine or the alpha 1-receptor agonists. Prazosin (10(-7) M), an alpha 1-receptor antagonist, produced a rightward shift in the concentration-response curve to norepinephrine, yielding apparent dissociation constants of 1.7 and 1.2 X 10(-8) M for the afferent and efferent arteriole, respectively. Prazosin also antagonized the contractile effects of UK 14304 (apparent dissociation constants, 0.9 and 1.1 X 10(-8) M for afferent and efferent arterioles, respectively). The selective alpha 2-receptor antagonist, rauwolscine (10(-7) M), had no effect on norepinephrine-mediated vasoconstriction. These results confirm the presence of alpha-adrenoceptors on the glomerular arterioles that mediated vasoconstriction. Furthermore, these receptors appear to be exclusively of the alpha 1-subtype.