Binding of 3H-D-Pen2-D-Pen5-enkephalin to brain regions and spinal cord membranes of spontaneously hypertensive and normotensive Wistar-Kyoto rats.

Abstract

The binding of 3H-D-Pen2-D-Pen5-enkephalin (DPDPE), a highly selective delta-opiate receptor agonist, to membranes of discrete brain regions and spinal cord of 10-week-old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were amygdala, hippocampus, hypothalamus, pons and medulla, corpus striatum, midbrain and cortex. 3H-DPDPE bound to membranes of brain regions and spinal cord at a single high affinity site with apparent dissociation constant value of 4 nmol/l, except in cortex where the values were higher. The highest density of 3H-DPDPE binding sites were in hypothalamus and lowest in pons and medulla. The receptor density (Bmax value) and apparent dissociation constant (Kd value) of 3H-DPDPE to bind to delta-opiate receptors on the membranes of hippocampus, hypothalamus, corpus striatum, midbrain, cortex, pons and medulla and spinal cord of WKY and SHR rats did not differ. The Bmax value of 3H-DPDPE in amygdala of SHR rats was higher than in WKY rats, but the Kd values in the two strains did not differ. It is concluded that SHR rats have a higher density of delta-opiate receptors, labeled with 3H-DPDPE, in amygdala in comparison with WKY rats. Whether such a difference in the density of delta-opiate receptors is related to the elevated blood pressure of SHR rats is not clear.