a1-Adrenergic Receptor Subtypes in Human Peripheral Blood Lymphocytes

We investigated the expression of a1-adrenergic receptor subtypes in intact human peripheral blood lymphocytes using reverse transcription–polymerase chain reaction (RT-PCR) and radioligand binding assay techniques combined with antibodies against the three subtypes of a1-adrenergic receptors (a1A, a1B, and a1D). RT-PCR amplified in peripheral blood lymphocytes a 348-bp a1A-adrenergic receptor fragment, a 689-bp a1B-adrenergic receptor fragment, and a 540-bp a1D-adrenergic receptor fragment. Radioligand binding assay with [ H]prazosin as radioligand revealed a high-affinity binding with a dissociation constant value of 0.6560.05 nmol/L and a maximum density of binding sites of 175.3620.5 fmol/10 cells. The pharmacological profile of [H]prazosin binding to human peripheral blood lymphocytes was consistent with the labeling of a1-adrenergic receptors. Antibodies against a1A-, a1B-, and a1D-receptor subtypes decreased [H]prazosin binding to a different extent. This indicates that human peripheral blood lymphocytes express the three a1-adrenergic receptor subtypes. Of the three different a1-adrenergic receptor subtypes, the a1B is the most represented and the a1D, the least. Future studies should clarify the functional relevance of a1-adrenergic receptors expressed by peripheral blood lymphocytes. The identification of these sites may represent a step for evaluating whether they represent a marker of a1-adrenergic receptors in cardiovascular disorders or for assessing responses to drug treatment on these receptors. (Hypertension. 1999;33:708-712.)