| Abstract: | The effect of (+)- and (-)-tranylcypromine (TCP), (-)-deprenyl and pargyline was tested and the interaction of these MAO inhibitors with tyramine and noradrenaline was compared on the circulation of the cat and on the isolated guinea-pig atria. 1. Anesthetised cats: An i.v. injection of 1 mg/kg of (+)- as well as (-)-TCP leads to an increase in the blood pressure and dp/dtmax. This effect is getting weaker on repeated doses. (-)-Deprenyl and pargyline decrease blood pressure and dp/dtmax. After a preadministration of (+)-TCP or pargyline the effect of tyramine on the blood pressure and contractility is prolonged. (-)-TCP prolongs slightly the cardiac effect of tyramine and is less effective than (+)-TCP. (-)-Deprenyl does not influence the effect of tyramine. The noradrenaline effect is not affected by the MAO-inhibitors. 2. Conscious cats: An i.v. injection of (+)- as well as (-)-TCP increases the blood pressure and decreases the heart rate. Desipramine (DMI) blocks this effect. Preadministration of (+)- as well as (-)-TCP and pargyline, but not (-)-deprenyl, potentiates the effect of tyramine on the blood pressure. According to this activity one can arrange these MAO-inhibitors as follows: (+)-TCP greater than (-)-TCP greater than pargyline. 3. Atrial preparations of guinea pigs: (+)- and (-)-TCP have a positive inotropic effect at concentrations from 10(-6) to 10(-5) mol/l, which is blocked by bupranolol and DMI. A pretreatment with reserpine prevents the effect of (-)- and weakens that of (+)-TCP. (+)-TCP, pargyline and (-)-deprenyl potentiate the effect of tyramine, while that of noradrenaline is potentiated by (+)- as well as (-)-TCP and (-)-deprenyl. |
