Age-dependent increases of immunoreactive imidazoline receptors in the human brain: possible association of a 29/30 kDa protein with the I2-imidazoline receptor identified by [3H]idazoxan.

In the postmortem human brain (15 specimens of frontal cortex), the immunodetection and quantification of imidazoline receptor (IR) proteins (29/30 and 47 kDa) and the specific binding of [3H]idazoxan to I2-IR were determined in parallel to study the effect of aging (range 3-89 years) on these proteins and its possible association. The immunoreactivity of the 29/30 kDa IR protein, similar to the I2-IR, showed a significant positive correlation with the age of the subjects at death (r = 0.54; P = 0.04). Moreover, the levels of this IR protein also correlated significantly with the density of I2-IR in the brain of the same subjects (r = 0.67; P = 0.01). It is suggested that the I2-IR labeled by [3H]idazoxan in the human brain is related to the 29/30 kDa IR protein identified by immunoblot analysis.