Objectives: Activating autoantibodies (AA) to the AT1R second extracellular loop (ECL2) are present in patients with primary aldosteronism (PA). We investigated whether AA from PA and from AT1R-ECL2 immunized rabbits activate AT1R and thereby contribute to hypertension by a direct contractile effect on the vasculature and stimulate adrenal aldosterone production.
Methods: We studied 5 normal controls (NC) and 15 subjects with biochemically confirmed PA [4 APA, 4 IAH non- and 7 indeterminate (IPA)]. AT1R-AA activity in serum or IgG was analyzed in AT1R transfected CHO cells. Contractile effects were assayed in isolated perfused rat cremaster arteries. We determined the effects of an ARB and the L-aa AT1R-ECL2 target epitope on in vitro AT1R cremaster artery responsiveness to patient sera and to MAP-L-aa (AFHYESQ) peptide immunized rabbit serum. We examined the effect of IgG from 7 PA subjects on aldosterone production in HAC15 cells in vitro w/wo 1.0 and 10 nM Ang II; and w/wo ARB.
Results: Serum from PA significantly (p<0.05) increased Ang II-equivalent activity in AT1R-CHO cells in IAH 199± x pM, n=4; APA 177±y pM, n=3; IPA 187±z pM, n=7; vs NC 83±a pM, n=5 and was blocked by 10 μM losartan. IgG from PA decreased perfused rat arteriole diameter in IAH by 22±8(SD)% of a 100% (normalized) baseline, n=4; APA 14±0.8%, n=3; IPA 21±6%, n=7; and NC 7±3.5%, n=5 and was blocked by 10 μM losartan. IgG from 7 PA subjects increased HAC15 aldosterone (aldo) 1.8 fold over baseline (p<0.01) and markedly increased 1nM and 10 nM Ang II-induced aldo by 3.5 fold (p<0.01); and was blocked by ARB. BP in hi Na rabbits rose from 80/60 to 140/90 6 weeks after immunization with AT1R MAP-L-aa AFHYESQ peptide. Arteriole contraction rose from 5% (preimmune) to 30% (post-immunization). Preincubation with the L-aa 2nd ECL target reduced contractility to 8%; not different from baseline.
Conclusions: AA from PA and AT1R-immunized rabbits activates AT1R transfected CHO cells, increases in vitro arterial contractility and stimulates basal and Ang II induced HAC15 aldosterone secretion. ARBs and decoy peptides were effective in blocking AA effects in vitro. These AA have important etiological and therapeutic implications.