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. 2014 Feb 28;3(1):e000755. doi: 10.1161/JAHA.113.000755

Figure 5.

Figure 5.

Allosteric effects of POTS serum/IgG on phenylephrine and isoproterenol dose response. A, Serum (1:200) from 3 POTS subjects with α1AR activating activity shifted the phenylephrine (PE) dosage response curve to the right in a cremaster vasoconstriction assay. Control serum failed to alter the curve. B, Serum (1:200) from 3 POTS subjects was incubated with prazosin (10 μmol/L, to block coexisting α1AR pressor activity) and used to construct an isoproterenol (ISO) vasodilator response curve in the cremaster arteriole assay. In contrast to the α1AR autoantibody dosage response, the β2AR activation curve was shifted significantly to the left compatible with a positive allosteric effect. C, Likewise, IgG (50 μg/mL) from 3 β2AR antibody‐positive POTS subjects significantly shifted to the left an isoproterenol activation curve of cAMP production in β2AR‐transfected CHO cells. D, IgG (50 μg/mL) from 3 POTS subjects containing β1AR autoantibodies produced a similar leftward shift of an isoproterenol activation curve in β1AR‐transfected CHO cells. *P<0.05, **P<0.01. AR indicates adrenergic receptors; CHO, Chinese hamster ovary; PRAZ, prazosin; POTS, postural tachycardia syndrome.