Characterization of [125I]beta-endorphin binding sites in the rat caudal dorsomedial medulla.
[125I]beta-endorphin bound to high affinity (Kd = 0.25 nM) receptors in the caudal dorsomedial medulla of rats with a Bmax of 97 fmol/mg protein. The relative potency for displacement of [125I]beta-endorphin binding was: beta-endorphin(1-31) > beta-endorphin(1-27) > DAMGO > naloxone > N-acetyl-beta-endorphin(1-31) > U50488 > DPDPE. The Bmax for [3H]DAMGO binding was 81 fmol/mg protein, indicating that most [125I]beta-endorphin binding corresponds to mu-opioid receptors. [3H]DAMGO binding was not influenced by lesioning noradrenergic nerve terminals in the caudal dorsomedial medulla. Our findings indicate that beta-endorphin interacts primarily with mu-opioid receptors in the caudal dorsomedial medulla. These receptors are not affected by noradrenergic denervation.
D'Souza
M M
MM
Department of Biological Sciences, Texas Tech University, Lubbock 79409-3131, USA.
Carr
J A
JA
D000818:Animals; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007457:Iodine Radioisotopes; D016015:Logistic Models; D008297:Male; D008526:Medulla Oblongata / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000032:analysis*
D007457:Iodine Radioisotopes; D011957:Receptors, Opioid; D016244:Guanosine 5'-O-(3-Thiotriphosphate)