Hypotensive and bradycardic effects of classical alpha-sympathomimetic drugs upon intravenous administration to pentobarbitone-anaesthetized rats.

The effects of the classical alpha-sympathomimetic drugs naphazoline, tramazoline, xylometazoline, tetryzoline and oxymetazoline on blood pressure and heart rate of pentobarbitone-anaesthetized (75 mg/kg; i.p.) normotensive rats were studied following intravenous injections. With the aid of this experimental animal model a dose dependent decrease in mean arterial pressure and heart rate could be established for these agents, oxymetazoline excepted, for which only the bradycardia could be quantified. It is suggested that central alpha-adrenoceptors are involved in the mechanism of this cardiovascular inhibition in view of the most specific alpha-adrenoceptor-stimulating properties of these ddrugs. Additionally, the results indicate that the use of pentobarbitone as the anaesthetic enhances the hypotensive action of these agents, so that their pronounced peripheral vasopressive response can be overcome.