The action of D-tubocurarine and of decamethonium on respiratory and other muscles in the cat / by W.D.M. Paton and Eleanor J. Zaimis.

  • Paton, William D. M.
Date:
[1951?]
Catalogue details

Licence: In copyright

Credit: The action of D-tubocurarine and of decamethonium on respiratory and other muscles in the cat / by W.D.M. Paton and Eleanor J. Zaimis. Source: Wellcome Collection.

    14/24 (page 324)
    depressed. This, too, is a regular phenomenon, and we have been able again to estimate the relative sensitivities of the two muscles; it needs about 30- 50 % more decamethonium to paralyse soleus than to paralyse tibialis. These differences do not represent a variation in the amount of injected drug reaching the two muscles. The experiments with simultaneous recording from the two muscles were undertaken so that the comparison between the muscles should be made while each was exposed to the same concentration of paralysing drug in the blood. But it is conceivable that the rates of blood flow in each muscle, and hence of uptake of a drug, might differ. This cannot have affected the results, however, because the exposure to the drug lasts for a considerable time, a period many times longer than the circulation time (cf. Gray & Paton, 1949). Further, the time of onset of paralysis and the time of maximum effect would have been different in the two muscles, if differences in speed of reaching equilibrium with the circulating drug had existed; in fact, however, these times were always the same for the two muscles. The differences in depth of paralysis must, therefore, be due to differences in sensitivity to the drug. Figs. 7 and 8 include records of the respiratory minute volume. In Fig. 7 it is not possible to say whether the respiratory muscles are following soleus or tibialis the more closely, since the depression of the tetanus by D-tubocurarine is substantial in both muscles. But in similar experiments, with slightly smaller doses, we have seen depression of the respiration where neither twitch nor tetanus of tibialis were much affected, but soleus was considerably blocked. In Fig. 8, after an injection of decamethonium, by which twitches and tetani are almost equally paralysed, there is still clearer evidence that soleus parallels the behaviour of the respiratory muscles; for although tibialis is 80 % paralysed, soleus is hardly affected, and the respiration not at all. Our results establish, therefore, that tibialis and soleus differ considerably in their sensitivity to decamethonium and to D-tubocurarine, and that of these two muscles, soleus resembles the respiratory muscles much more closely than does tibialis in its response to these drugs. Sensitivity of the diaphragm It follows from what has been already described, that the diaphragm should be more sensitive to D-tubocurarine than to decamethonium. We are greatly indebted to Dr Wien for testing this point for us on the isolated rabbit and kitten diaphragms in vitro. Using single shocks at a rate of 8/min., he found that on the rabbit diaphragm, decamethonium was one-quarter as active as D-tubocurarine; and on the kitten diaphragm, one-half as active as D-tubo¬ curarine. Since, with the rabbit head-drop test decamethonium is roughly twice as active as D-tubocurarine, and with tibialis twitch in cat about fifteen times as active, it is clear that in these species the diaphragm is relatively resistant to decamethonium.