title: Pituitary thyrotropin-releasing hormone (TRH) receptors: effects of TRH, drugs mimicking TRH action, and chlordiazepoxide.
abstract: Binding of TRH to specific cell surface receptors on clonal GH4C1 cells is followed within 10 min by receptor sequestration and over 24 h by receptor down-regulation. These experiments were designed to determine if TRH-activated second messenger systems are responsible for changes in receptor localization or number. BAY K8644 and A23187, which increase intracellular calcium, alone or together with 12-O-tetradecanoyl phorbol acetate (TPA), which activates protein kinase C, did not appear to internalize TRH receptors. Drug treatment did not alter the rate of [3H]MeTRH association or internalization, determined by resistance to an acid/salt wash, or the amount of [3H]MeTRH able to bind at 0 C, where only surface receptors are accessible. TPA (0-100 nM) alone or in combination with BAY K8644 or A23187, also failed to change receptor number or affinity after 48 h when TRH caused a 75% decrease in the density of specific binding sites. Chlordiazepoxide has been reported antagonize TRH binding and TRH-induced phospholipid breakdown. Chlordiazepoxide shifted the dose-response curves for TRH stimulation of PRL release and synthesis to the right, and did not change PRL release alone. The affinity of receptors for chlordiazepoxide was not affected by a nonhydrolyzable analog of GTP whereas affinity for TRH was decreased; these properties are consistent with the classification of chlordiazepoxide as a competitive antagonist. Several experiments tested whether chlordiazepoxide would cause receptor internalization and down-regulation. Chlordiazepoxide did not appear to internalize TRH receptors, because TRH-binding sites became available rapidly and at the same rate after they had been saturated with chlordiazepoxide at 0 or 37 C.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Pharmacology, University of Rochester School of Medicine and Dentistry, New York 14642.
authors: P M
authors: PM
authors: Hinkle
authors: E D
authors: ED
authors: Shanshala
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D000001:Calcimycin / Q000494:pharmacology; D002460:Cell Line; D002707:Chlordiazepoxide / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects; D009553:Nimodipine / Q000494:pharmacology; D010902:Pituitary Gland / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D017981:Receptors, Neurotransmitter / Q000187:drug effects*; D018025:Receptors, Thyrotropin-Releasing Hormone; D013755:Tetradecanoylphorbol Acetate / Q000493:pharmacokinetics / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D017981:Receptors, Neurotransmitter; D018025:Receptors, Thyrotropin-Releasing Hormone; D000001:Calcimycin; D009553:Nimodipine; D013973:Thyrotropin-Releasing Hormone; D002707:Chlordiazepoxide; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011388:Prolactin; D013755:Tetradecanoylphorbol Acetate