Facilitatory and inhibitory effects of harmaline on the tryptophan-induced 5-hydroxytryptamine syndrome and body temperature changes in pargyline-pretreated rats.
The effects of harmaline on tryptophan-induced 5-hydroxytryptamine (5HT) syndrome and body temperature changes in pargyline-pretreated rats were investigated. When administered i.p. 60 min after pargyline treatment (50 mg/kg, i.p.), tryptophan, at 100 mg/kg but not 10 mg/kg, induced the 5-HT syndrome. Tryptophan at 100 mg/kg also produced hypothermia followed by hyperthermia in pargyline-pretreated rats. Administration of harmaline (10 mg/kg, i.p.) 30 min after pargyline not only potentiated the 100 mg/kg tryptophan-induced 5-HT syndrome and body temperature changes, but also produced the syndrome following administration of 10 mg/kg tryptophan in pargyline-pretreated rats. In contrast, when administered 30 min before parygline, 10 mg/kg harmaline completely suppressed the syndrome and body temperature changes caused by mg/kg tryptophan. Tryptophan (100 mg/kg, i.p.) administration significantly increased 5-HT levels and decreased 5-hydroxyindole acetic and levels and 5-HT turnover in the brain of pargyline-pretreated rats. Harmaline administration 30 min after pargyline did not significantly affect the tryptophan-induced changes in 5-HT levels and 5-HT turnover, whereas when administered 30 min before pargyline, harmaline significantly blocked the effect of tryptophan. These results suggest that mechanisms underlying the inhibitory action of harmaline on the tryptophan-induced 5-HT syndrome and body temperature changes in pargyline-pretreated rats differ from those by which harmaline potentiates the effects of tryptophan.
Division of Pharmacology, Research Institute for Wakan-Yaku (Oriental Medicines), Toyama Medical and Pharmaceutical University, Japan.
A F
AF
Abdel-Fattah
K
K
Matsumoto
Y
Y
Murakami
K A
KA
El-Hady
M F
MF
Mohamed
H
H
Watanabe
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001833:Body Temperature Regulation / Q000187:drug effects*; D006246:Harmaline / Q000494:pharmacology*; D008297:Male; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D010293:Pargyline / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*; D013577:Syndrome; D014364:Tryptophan / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D008996:Monoamine Oxidase Inhibitors; D012701:Serotonin; D014364:Tryptophan; D010293:Pargyline; D006246:Harmaline