Effects of tetramethylpyrazine on heart rate and pupil diameter in rats.
The alpha-adrenergic nature of tetramethylpyrazine (TMPZ), a commonly used cardiovascular drug in China, was studied with a combined bradycardia and mydriasis model in the pentobarbital anesthesized rat. Intravenous injections of TMPZ at 1-30 mg/kg failed to change heart rate or pupil size, whereas iv injections of both clonidine (alpha 2-adrenoceptor agonist, 1-30 micrograms/kg) and methoxamine (alpha 1-adrenoceptor agonist, 10-300 micrograms/kg) caused dose-dependent bradycardia and mydriasis. Pretreatment of rats with TMPZ (30 mg/kg) did not significantly change clonidine- or methoxamine-induced bradycardia or mydriasis. However, when TMPZ was injected 2 min after clonidine administration (30 micrograms/kg), while the mydriasis reached a maximum, it slightly but significantly reversed the clonidine-induced mydriasis for 15-20 s. In contrast, the alpha 2-adrenoceptor antagonist idazoxan (6 micrograms/kg) caused the same degree of reduction of the clonidine-induced mydriasis for greater than 2 min. Our results suggested that TMPZ at the doses studied did not have alpha-adrenoceptor agonistic activities, but may have slight alpha 2-adrenoceptor antagonistic activities.
Hsu
W H
WH
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames 50011.
Smith
B E
BE
D000818:Animals; D006339:Heart Rate / Q000187:drug effects*; D007275:Injections, Intravenous; D008297:Male; D011680:Pupil / Q000187:drug effects*; D011719:Pyrazines / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D011719:Pyrazines; C017953:tetramethylpyrazine