Abstract

The simultaneous changes in tooth pulp threshold and respiratory minute volume in rabbits have been measured following i.v. morphine or levorphan, or combinations of levorphan and levallorphan. In general, it appeared that levorphan was at least twice as active as morphine on a molar basis in producing increases in tooth pulp threshold, and, for equal increases in tooth pulp threshold, levorphan produced less prolonged depression of respiratory minute volume than morphine at doses below 0.008 and 0.016 millimole/kgm., respectively.

When a constant dose of levorphan was administered simultaneously with varying amounts of levallorphan, there was no evidence of preferential antagpnism of the respiratory minute volume depression over the tooth pulp threshold changes. Further, in no case, did combinations fail to give depression of respiratory minute volume and elevation of tooth pulp threshold. However, on increasing the dose of combined drugs in the ratio of one part levallorphan to five parts of levorphan, it was possible to obtain elevations in tooth pulp threshold equivalent to those produced by 0.002 millimole/kgm. levorphan alone with sighificantly less respiratory nimute volume depression.