Effects of an anaesthetic on plasma levels of histamine and tele-methylhistamine in the cat.

The effects of intravenous injection of ketamine on plasma levels of histamine (Hi) and its metabolite, tele-methylhistamine (MeHi) were studied in the cat. The results showed that the anaesthetic, given in doses which prolonged anaesthesia in the cat (2.5-7.5 mg/kg) caused Hi release, which raised the concentrations of Hi in plasma up to 1600%. It was followed by a slower and also significant increase of plasma MeHi levels (up to 1200%). When urethane was used as an anaesthetic no changes of plasma levels were noticed. However, about 50% of i.v. injections of Ringer-Locke solution were followed by a transient increase of plasma Hi and MeHi concentrations.