Figure 4: Vasoactive effects of supernatant-derived from myocytes in isolated coronary arterioles treated with 8-PSPT to block adenosine receptors. Myocyte-derived supernatant was obtained from myocytes treated with phenylephrine or simultaneously treated with phenylephrine and prazosin. Addition of the -adrenergic receptor antagonist, prazosin, to myocytes prevented the production of a vasoconstrictor compound in the supernatant and eliminated constriction of the isolated arterioles. Direct administration of prazosin to isolated arterioles was without effect, indicating that α-adrenergic constriction is not due to direct effects on arteriolar smooth muscle. Administration of the antagonist to the isolated arterioles abolished the constrictor response that was observed during exposure to myocyte-derived supernatant. versus other groups; versus baseline. Adapted from Teifenbacher et al. , with permission.