Localization of mRNA for three distinct α₁-adrenergic receptor subtypes in human tissues: Implications for human α-adrenergic physiology

α₁-Adrenergic receptors (α₁ARs) are virtually ubiquitous in human tissues and mediate important physiological functions as diverse as smooth muscle contraction, glycogenolysis, and myocardial inotropy. At least three α₁AR subtypes (α(1A/D), α(1B), and α(1C)) have been described using molecular and pharmacological techniques. The identification of species heterogeneity (rat versus rabbit) in α₁AR subtype distribution has made it imperative to determine the distribution of α₁AR subtypes in human tissues. Accordingly, RNA extracted from human tissues was analyzed using RNase protection assays to determine α₁AR subtype expression. Of the cloned α₁ARs, α(1C)AR mRNA predominates in many human tissues (heart, liver, cerebellum, and cerebral cortex), in contrast to its restricted distribution in both rats and rabbits. α(1B)AR mRNA is present in highest concentrations in human spleen, kidney, and fetal brain. α(1A/D)AR mRNA is present in highest concentrations in human aorta and cerebral cortex. Hence, α₁AR subtype mRNA distribution is tissue selective and differs from that reported for rats and rabbits. These results have potentially significant implications for understanding human adrenergic physiology and are important for the rational development of α₁AR subtype-selective drugs.