Agonist-induced desensitization of the D-2 dopamine receptor in the intermediate lobe of the rat pituitary gland.

Published

Journal Article

The mechanism of agonist-induced desensitization of the D-2 dopamine receptor in the intermediate lobe (IL) of the rat pituitary gland was investigated. Exposure of neurointermediate lobe to 60 microM (-)apomorphine (APO) for 60 min altered the binding of [125I]-N-(p-aminophenethyl)spiperone (NAPS), a D-2 receptor-specific ligand. The capacity of the tissue to bind the ligand (Bmax) was not significantly altered by the exposure to (-)APO but the affinity for [125I]NAPS was decreased 3.6-fold in (-)APO-exposed tissue. The molar potency of YM-09151-2, a D-2 receptor-specific antagonist, showed a minimal difference between in control and (-)-APO-exposed tissue. However, the molar potency of (-)APO towards the D-2 receptor was diminished. The loss of [125I]NAPS binding in (-)APO-exposed tissue was reversed by the addition of guanyl nucleotide. These data suggest that exposure to agonist causes a persistent occupancy of the high affinity state of the receptor. Exposure to (-)APO had no effect on either basal or forskolin-activated adenylate cyclase activity of the intermediate lobe. However, the inhibitory effect of (-)APO upon adenylate cyclase activity of IL homogenates was diminished when the tissue was exposed to (-)APO before homogenization. Furthermore, the ability of GTP but not 5'-guanylyl imidodiphosphate [Gpp(NH)p] to inhibit enzyme activity diminished in the (-)APO-exposed tissue. These data suggest that an agonist-induced desensitization of D-2 receptor in rat IL is thought to occur by uncoupling the receptor from the inhibitory guanyl nucleotide binding protein (Gi) or potentiating the hydrolysis of GTP by Gi.

Full Text

Duke Authors

Cited Authors

  • Agui, T; Amlaiky, N; Caron, MG; Kebabian, JW

Published Date

  • March 1988

Published In

Volume / Issue

  • 103 / 3

Start / End Page

  • 436 - 441

PubMed ID

  • 3391998

Pubmed Central ID

  • 3391998

International Standard Serial Number (ISSN)

  • 0021-924X

Digital Object Identifier (DOI)

  • 10.1093/oxfordjournals.jbchem.a122288

Language

  • eng

Conference Location

  • England