Effect of analeptics on brain pentobarbital levels and sleeping time in mice.

IN THE treatment of barbiturate poisoning the therapeutic emphasis has shifted from the use of analeptics and efforts at arousal to a regimen of physiologic supportive therapy.1 For some time, though, analeptics were drugs of choice, the results being transferred from experimental evidenceQ* 3 despite some reports49 5 about the ineffectiveness of these drugs in animals given large doses of barbiturates. Theoretically, stimulant therapy with drugs like nikethamide, pentylenetetrazol and picrotoxin might seem appropriate. Nilsson,Q and subsequently others,7* * have given up their use hecause of severe untoward side effects and higher mortality. According to Nilsson, when the nervous system is doubly challenged by the depressant action of one compound and the stimulant action of another, the system tends towards instability and the resultant patterns of nervous activity are abnormal. In a previous experiment9 we observed that mice given hexobarbital and nikethamide simultaneously showed a tremendous increase in the sleeping time (loss of righting reflex), even though there were convulsive movements and increased respiration during sleep. In the present report we have extended this observation to an examination of the brain-barbiturate levels, using pentobarbital as the depressant and nikethamide, pentylenetetrazol and pictrotoxin as analeptics. Female white mice (Haffkine Institute strain) weighing between 25-28 g were used throughout the experiments. For barbiturate estimation brains of three mice were pooled after decapitation and dissection. The samples were duplicated after extraction in petroleum ether and estimated spectrophotometricallylo with a modificationll where the final extraction was in 0.5 N NaOH. This method is specific for unchanged barbiturate. The specificity of this method of estimating pentobarbital was confirmed by chromatographing the petroleum ether extract of the pooled brains on thin layer (silica gel G + alumina, 1:l) using cyclohexane-isopropanol and ammonia solution as a solvent system.12 This method gave only one U.V. spot with an Rf value of 0.85. The anleptics used did not show any change in this spot and did not give a U.V. spot themselves when used concurrently as standards. The sleeping time was studied in groups of mice and was considered as the interval between the loss of righting reflex after injection and the regaining of the righting reflex (thrice within a minute), measured by a stop watch. The time has been expressed only in minutes, the seconds being rounded off to the nearest minute. Table 1 shows all the results. It can be seen that treatment with analeptics increases the brain barbiturate level to many times the control. Even where the sleeping time is decreased, as with picrotoxin, the barbiturate level in brain is high. There does not seem to be any particular waking level of brain barbiturate after treatment with analeptics. The stimulation of the central nervous system with analeptics might alter the cellular permeabilities to favor an excess entry of the barbiturate. This would cause a delay in the excretion of barbiturate and the higher mortality with the use of analeptics observed in other literature.13-l6