title: Sodium and guanine nucleotide regulation of dopamine receptor agonist and antagonist binding sites in MtTW15 pituitary tumors.
abstract: The modulation of the dopamine receptor in MtTW15 tumors was investigated. The antagonist dopaminergic binding site in MtTW15 tumors labelled with [3H]spiperone remains unchanged at 25 degrees C in the presence or absence of sodium or guanine nucleotides (Gpp(NH)p); by contrast at 37 degrees C sodium increases the affinity while Gpp(NH)p decreases it slightly. The dopamine receptor in this tumor, such as the intact adenohypophysis, exists in a high and low affinity state for dopamine agonists. These agonist affinity states evaluated with apomorphine competition for [3H]spiperone binding show similar affinities as those of intact tissue but have a lower proportion of the high affinity state. At 25 degrees C, a partial conversion of the high into the low affinity state is obtained in the presence of both sodium and Gpp(NH)p, while at 37 degrees C a complete conversion is observed. These data show differences in the modulation of antagonist and agonist dopaminergic binding sites in MtTW15 pituitary tumors compared with the intact pituitary.
authors: School of Pharmacy, Laval University, Québec, Canada.
authors: T
authors: T
authors: Di Paolo
authors: D
authors: D
authors: Lévesque
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D005260:Female; D006150:Guanine Nucleotides / Q000502:physiology*; D009368:Neoplasm Transplantation; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D011920:Rats, Inbred WF; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D013134:Spiperone
chemical_list: D006150:Guanine Nucleotides; D011954:Receptors, Dopamine; D013134:Spiperone; D012964:Sodium