title: In vitro effect of thyroxine on cholinergic neurotransmission in rat sympathetic superior cervical ganglion.
abstract: This study aimed at examining the effect of thyroid hormones on cholinergic transmission in isolated rat superior cervical ganglia (SCG). In SCG explants incubated with 3H-choline, thyroxine (T4) and 3,3',5-triiodothyronine (T3) added to the medium before a second depolarization stimulus of 60 mM K+ resulted in a dose-dependent increase of S2/S1 ratio for 3H release. The concentration of hormone that produced 50% of maximal increase in K(+)-induced radioactivity release was 8 x 10(-9) M for T4 and 1.6 x 10(-8) M for T3 while 3,3',5,5'-tetraiodothyroacetic acid was almost ineffective. Preincubation of SCG with 10(-7) M iopanoic acid for 30 min before S2, although not affecting by itself S2/S1 ratio, effectively prevented the increase given by T4 or T3. 3H-acetylcholine release by SCG was augmented in a high K+, and the effect was amplified by T4 to a similar extent as that for total 3H release. When added to the incubation medium together with 60 mM K+ for 30 min, T4 (10(-7) M) increased significantly the activity of choline acetyltransferase (ChAT). T4 did not affect ChAT activity in SCG exposed to 4.7 mM K+, nor in SCG homogenates. 3H-choline uptake measured immediately after exposure of SCG to 60 mM K+ decreased by 25%, whereas it increased by 71% after a subsequent 30-min incubation with 4.7 mM K+. Addition of 10(-7) M T4 prevented the changes in choline uptake observed in a high K+ medium. These results indicate that T4 increases SCG cholinergic transmission.
authors.affiliation: Departamento de Fisiología, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
authors.forename: M E
authors.initials: ME
authors.lastname: Landa
authors.forename: G
authors.initials: G
authors.lastname: González Burgos
authors.forename: D P
authors.initials: DP
authors.lastname: Cardinali
mesh_terms: D000818:Animals; D002794:Choline / Q000378:metabolism; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D005728:Ganglia, Sympathetic / Q000187:drug effects* / Q000378:metabolism; D010275:Parasympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D009435:Synaptic Transmission / Q000187:drug effects*; D013974:Thyroxine / Q000494:pharmacology*; D014316:Tritium
chemical_list: D014316:Tritium; D002795:Choline O-Acetyltransferase; D002794:Choline; D013974:Thyroxine