title: Effect of neurotransmitters on the in vitro release of immunoreactive thyrotropin-releasing hormone from rat mediobasal hypothalamus.
abstract: The in vitro release of TRH from hypothalamic fragments or purified nerve endings (synaptosomes) has been evaluated after incubation for 10 min in the presence of various concentrations of K+ or neurotransmitters. Release of the hormone from fragments but not from synaptosomes was enhanced in the presence of 56 mM K+ in a Ca++ -dependent manner. Neurotransmitter effects were thus tested on the fragments. Addition of histamine (10 (-7)-10(-5) M) induced a significant increase over the basal release of TRH. A comparable effect was obtained with dimaprit (10(-5) M), a highly specific agonist of histamine H2 receptors; conversely, the response to histamine was blocked by the addition of a H2 (metiamide; 10(-6) M) but not of a H1 (mepyramine; 10(-6) M) antagonist to the incubation medium. Dopamine (10(-7) M) slightly inhibited the release of TRH, but antagonists of dopamine receptors (10(-7)-10(-6) M fluphenazine or 10(-6) M alpha-flupentixol) exhibited an inhibitory effect by themselves, so that specific receptors involved in mediating dopamine actions could not be further characterized. In contrast, noradrenalin, serotonin gamma-aminobutyric acid and acetylcholine (tested at concentration of 10(-7) M) did not alter the basal release of the tripeptide.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004298:Dopamine / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D018377:Neurotransmitter Agents; D012701:Serotonin; D008785:Metiamide; D005680:gamma-Aminobutyric Acid; D013973:Thyrotropin-Releasing Hormone; D006632:Histamine; D007770:L-Lactate Dehydrogenase; D011188:Potassium; D004298:Dopamine; D009638:Norepinephrine