1. After the development of tachyphylaxis to ephedrine in rats, the dose-pressor-response curve of tyramine was depressed (Fig. 7), while that of noradrenaline was not altered significandy.

2. OBJECTIVE:To study the tachyphylaxis after pseudo ephedrine and ephedrine crossly used on isolated guinea pig tracheae.

3. If noradrenaline was infused after tachyphylaxis, it could partially restore the pressor effect of ephedrine injected during the infusion (Fig. 8).

4. Tachyphylaxis to ephedrine has been studied on the cat's nictitating membranes, the cat's and the rat's blood pressure.

5. The results of our study demonstrate that, at dopamine tachyphylaxis of canine tracheal smooth muscle, histamine treatment could recover the contraction to dopamine.

6. Short term tolerance can be caused by depleted levels of neurotransmitters within the vesicles available for release into the synaptic cleft following subsequent reuse ( tachyphylaxis ).