Quantitative autoradiography of alpha 2 agonist binding sites in the spontaneously hypertensive rat brain.

The relative binding of the alpha 2 agonist [3H]para-aminoclonidine ([3H]PAC) was examined in discrete regions of the spontaneously hypertensive (SHR) and WKY normotensive rat brains by quantitative autoradiography. Substantially less binding was noted in various brain nuclei known to influence cardiovascular function when comparing the SHR to WKY rat brains. These areas included the nucleus of the solitary tract, dorsal motor nucleus of the vagus, locus coeruleus and paraventricular nucleus of the hypothalamus. This difference in binding was also noted in the bed nucleus of the stria terminalis and the nucleus reuniens of the thalamus. Other brain areas which are not believed to be directly involved in central cardiovascular control such as the cerebral cortex, dorsal lateral geniculate and hippocampus exhibited no significant difference in binding between the two strains. Scatchard analysis of [3H]PAC binding indicated that the difference in binding may be due to a selective loss of the high affinity alpha 2 agonist sites in the SHR. These results indicate that a selective loss of alpha 2 receptors in discrete brain cardiovascular control regions of the SHR may contribute to the elevated blood pressure seen in this strain.