α-2A is the predominant α-2 adrenergic receptor subtype in human spinal cord

Abstract

α-2 Adrenergic receptors can be subdivided into four subtypes based on their pharmacologic properties. The subtype of α-2 adrenergic receptor present in human spinal cord has not been reported previously. The affinities of nine α-2 subtype-selective drugs for the α-2 adrenergic receptor in human spinal cord homogenates were determined using [3H]rauwolscine and [3H]RX821002. These drug affinities (pK(i) values) were highly correlated with those obtained in a tissue or cell line containing only the α-2A adrenergic subtype (correlation coefficient of 0.99 and 0.98 for human platelet and HT29 cells, respectively). In contrast, the correlation of pK(i) values for the human spinal cord with tissues or cell lines containing other adrenergic receptor subtypes was poor. The correlation coefficients for α-2B (neonatal rat lung), α-2C (OK cell), and α-2D (bovine pineal gland) were 0.15, 0.68, and 0.81, respectively. These data suggest that the predominant α-2 adrenergic subtype present in human spinal cord is the α-2A subtype. Both [3H]rauwolscine and [3H]RX821002 appeared to label a single class of binding sites. The α-2 adrenergic receptor density was significantly greater in the sacral region of the cord as compared to either the lumbar or thoracic regions.