Histamine and tele-methylhistamine in cat plasma after intravenous injection of histamine.
The effects of increased plasma histamine (Hi) on plasma tele-methylhistamine (MeHi) levels and the kinetics of Hi and MeHi elimination from plasma were studied in the cat. Hi (40 or 50 micrograms/kg) was injected intravenously and then Hi and MeHi were assayed by HPLC. Hi injection was followed by a significant increase in plasma MeHi levels, being maximal at 2-4 min. In most animals, maximal MeHi levels exceeded Hi itself. The half-lives (t1/2) of injected Hi were 0.6 and 13.3 min (mean values) in the alpha- and beta-phases, while the corresponding values for MeHi were 1.1 and 15.4 min. The t1/2 of exogenous MeHi (64 micrograms/kg, i.v.) was in the same range. Inhibitors of histamine-N-methyltransferase diminished the elimination rate of both amines studied. Plasma MeHi can thus serve as a marker for increased plasma Hi in the cat particularly because of its noticeable and delayed elevation after the rise in Hi itself.
Irman-Florjanc
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T
Department of Pharmacology, Medical Faculty, University of Ljubljana, Slovenia.
Erjavec
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F
D000818:Animals; D002415:Cats; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006207:Half-Life; D006632:Histamine / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology; D006637:Histamine N-Methyltransferase / Q000037:antagonists & inhibitors; D007275:Injections, Intravenous; D008297:Male; D008761:Methylhistamines / Q000097:blood*
D008761:Methylhistamines; D006632:Histamine; D006637:Histamine N-Methyltransferase; C020404:tele-methylhistamine