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 δ-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 (B_max value) and apparent dissociation constant (K_d value) of ³H-DPDPE to bind to δ-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 B_max value of ³H-DPDPE in amygdala of SHR rats was higher than in WKY rats, but the K_d values in the two strains did not differ. It is concluded that SHR rats have a higher density of δ-opiate receptors, labeled with ³H-DPDPE, in amygdala in comparison with WKY rats. Whether such a difference in the density of δ-opiate receptors is related to the elevated blood pressure of SHR rats is not clear.

Upregulation of tachykinin NK‐1 and NK‐3 receptor binding sites in the spinal cord of spontaneously hypertensive rat: impact on the autonomic control of blood pressure

“…treatment with antisense oligonucleotides evidenced a role for TRH projections to spinal sympathetic preganglionic neurons in the elevation of resting arterial blood pressure in SHR (Suzuki et al ., 1995). Receptor binding sites were increased for TRH (Bhargava & Gulati, 1988), yet they were unchanged for endothelin and delta‐opiate receptors (Gulati & Rebello, 1992; Bhargava & Rahmani, 1993) and reduced for nicotinic receptors (Khan et al ., 1994; 1996) in the spinal cord of SHR. This suggests specific upregulation in spinal cord neurotransmitters and receptors in SHR.…”

Endogenous opiates: 1993

“…Binding of DPDPE in the amygdala was greater in spontaneously hypertensive rats than in normals, but in other areas, such as the hippocampus, hypothalamus, corpus striatum, midbrain, cortex, pons, medulla, and spinal cord, there was no difference. It was not clear if the binding in the amygdala was related to the increased blood pressure in the genetically disposed rats, however, because the number of sites but not their affinity was greater (53).…”