Functional autoimmune epitope on alpha 1-adrenergic receptors in patients with malignant hypertension.

Because of the growing evidence that hypertensive disease is accompanied by immunological dysfunction, we have investigated autoimmunity in patients with malignant hypertension. Peptides corresponding to the sequence of the second extracellular loops of the human alpha 1-adrenergic receptor and the M2-muscarinic receptor were used as antigens in an ELISA. Serum from 4 (12%) of 33 healthy controls, 3 (20%) of 15 patients with malignant essential hypertension, and 7 (64%) of 11 with secondary hypertension showed positive responses in the ELISA for the alpha 1-adrenergic receptor peptide. Positive responses were significantly more common among the patients with secondary hypertension than in the other two groups (p < 0.01). By contrast, no autoantibodies against the M2-muscarinic receptor peptide were detected in either hypertensive group. Autoantibodies against the alpha 1-adrenergic receptor, affinity-purified from patients with positive responses, specifically recognised bands with molecular masses of 68, 40, and 37 kDa on immunoblotted membrane proteins of rat ventricles. The patients' autoantibodies caused a decrease in tritiated prazosin binding sites and an increase in heart beating frequency of neonatal cultured rat cardiomyocytes; antibodies purified from the controls had no effect. Circulating autoantibodies against the alpha 1-adrenergic receptor are present in a subgroup of patients with malignant hypertension. These autoantibodies have pharmacological activity in vitro, which suggests that they may be involved in the pathogenesis of malignant hypertension.

[Antigenicity study of terazosin].

Antigenicity of terazosin was studied in the experimental animals and the following results were obtained. Terazosin was shown to be non-immunogenic in guinea-pigs and mice when immunized alone or with mixture of terazosin and protein as immunogen. Protein-conjugate of terazosin induced responses of hapten specific antibody when guinea pigs and mice were immunized. However, terazosin alone was shown to be not capable of eliciting any allergic responses. In conclusion, terazosin lacks immunogenicity and eliciting antigenicity in these experimental conditions and this suggests that drug allergic response would either not occur or be minimal, if any, when terazosin is administered clinically.

Antibodies to the alpha 1- and alpha 2-selective antagonists prazosin and yohimbine as probes of the alpha-adrenergic binding sites.

Antibodies were raised against a newly synthesized analog (CP57,609) of the alpha 1-selective antagonist prazosin, and against the alpha 2-selective antagonist, yohimbine, by immunization of rabbits with antigens prepared by covalent linkage of these ligands to albumin. Competitive inhibition of [3H]prazosin binding to anti-CP57,609 antiserum by a variety of unlabeled ligands revealed a spectrum of antibody specificity, with alpha 1-selective agents competing more potently than alpha 2-selective ligands. In contrast, alpha 2-selective ligands competed more potently with the binding of [3H]yohimbine to the anti-yohimbine antiserum than alpha 1-selective agents. These respective antisera were subjected to affinity fractionation of a CP57,609- or yohimbine-Sepharose 4B resin. Fractions from the CP57,609 resin were eluted successively with phentolamine (10(-3)M), prazosin (10(-4)M), and guanidine (5M), and from the yohimbine resin with prazosin (10(-4)M), yohimbine (10(-4)M), and guanidine (5M). The binding profiles of these fractions differed, and in certain fractions the relative order of potency of adrenergic agents was almost identical to that observed with membrane alpha-adrenergic receptors. Moreover, using these eluted fractions as immunogens, antisera have been obtained which, in the initial bleeds, already possess antiidiotypic activity. These findings therefore suggest that affinity fractionation of antibodies raised against alpha 1- and alpha 2-selective antagonists may provide useful analogs for the further study of the ligand recognition properties of alpha-adrenergic receptors. Additionally, it is probable that antiidiotypic antisera will be developed which will recognize the alpha-adrenergic binding sites.

Influence of prazosin on the development of antinuclear antibodies in hypertensive patients.

A recent publication suggested that antinuclear antibodies (ANA) occur in up to one third of patients treated with the hypotensive drug prazosin (Minipress). We have examined a large group of hypertensive patients and found ANA in 9.7% of 145 patients taking prazosin and in 12.2% of hypertensive patients on any treatment regimen. Excluding patients taking methyldopa (a drug associated with a high ANA incidence), the ANA incidence fell to 6.9% in the prazosin-treated group and to 7.2% of all treated hypertensives. Of over 350 untreated hypertensive patients, 6.0% had ANA. Prazosin did not increase the ANA incidence in patients on or off various drug combinations including beta blockers and diuretics. Analysis of the data by age and sex confirmed our conclusion that prazosin therapy is not accompanied by an increase in ANA.