A NOTE CONCERNING THE ACTIONS OF PSEUDOMORPHINE

¹ From the Laboratory of Pharmacology, University of Pennsylvania

1. Pseudomorphine has practically no morphine-like effects upon the central nervous system; its actions appear to be due entirely to effects upon blood-vessels and heart qualitatively identical with those of morphine but much more intense. Like morphine, these circulatory effects are elicited only by intravenous injection in dogs and cats; rabbits, rats, and guinea-pigs are highly resistant.

2. Pseudomorphine causes immediate precipitation when mixed with blood-serum, but this has nothing to do with its physiological effects. This insolubility probably accounts for its ineffectiveness when given by routes other than intravascular.

3. Pseudomorphine readily produces "acute tolerance" of the circulation, not only to itself but to morphine, codeine, and heroin as well; dogs tolerant to subcutaneous injections of morphine are also tolerant to the depressor effects of pseudomorphine, codeine, and heroin. This effect of pseudomorphine is limited to the circulation: it does not modify the action of morphine upon the central nervous system and the gastrointestinal tract.

4. The symptoms which follow intravenous injection of pseudomorphine in normal dogs are very similar to those described as the result of acute withdrawal of morphine from chronically poisoned tolerant dogs, but the resemblance is only superficial, and there are outstanding points of dissimilarity.

5. It is concluded that pseudomorphine has nothing to do with the phenomena of tolerance to or withdrawal of morphine, with the possible exception of circulatory effects.