Abstract

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