In a previous paper (Laurence and Stacey, 1952a) we have shown that hexamethonium and pentamethonium protect mice and rats against nicotine convulsions to a marked degree, but that they afford no protection against the action of a number of other convulsants nor against insulin convulsions (Laurence and Stacey, 1952b). In the present work we have sought an explanation for this protection.Hexamethonium does not pass freely into the cerebrospinal fluid (Paton), so that there are good reasons for investigating possible peripheral mechanisms. Evidence has already been advanced for believing that, although violent stimulation of the carotid body may, according to Schmidt and Comroe (1940), lead to convulsions, it is not by blocking afferent impulses from this structure that hexamethonium exerts its protection (Laurence and Stacey, 1952a). Attention was therefore turned to other peripheral actions of nicotine which are modified by hexamethonium. Hexamethonium blocks stimulation of the adrenal medulla by nicotine, and it was thought possible that the adrenaline liberated might play a part in precipitating nicotine convulsions, since adrenaline is known to facilitate spinal reflexes (Bulbring and Burn, 1941) and the passage of impulses across synapses (Bulbring and Burn, 1942), and to potentiate the action of various substances on the central nervous system (Friedemann and Elkeles, 1932). The convulsant action of nicotine was therefore examined under conditions in which the effects of sympathetic stimulation were increased (by simultaneous administration of adrenaline or noradrenaline) or decreased (by blocking agents or adrenalectomy).
METHODSMice and rats were used. In each experiment a comparison was made between the convulsion rates in two groups of animals of the same sex, from the same colony, and of similar weights and ages which had received the same dose of a convulsant (either nicotine or leptazol). One group had received previously an injection of a solution of the drug whose anticonvulsant action was being examined, while the other had received an equal volume of solvent. For dibenamine the time interval between the two injections was four hours, for all other drugs 30 minutes.Mice were given nicotine (0.2 mg. base/ml.) or leptazol (2 mg./ml.) into a tail vein, the injection occupying exactly 10 seconds timed by a metronome. Premedication was by intraperitoneal injection. Rats received nicotine (2 mg. base/ml.) subcutaneously or leptazol (25 mg./ml.) intraperitoneally and premedication by subcutaneous injection. Each experiment was repeated after one week with the groups crossed over; the results were then summed. Doses of convulsants were adjusted to give a suitable convulsion rate for the purpose of the experiment. In mice these were: nicotine 0.2-0.4 mg./kg., leptazol 20-40 mg./kg.; and for rats: nicotine 2-3 mg./kg., leptazol 50-70 mg./kg. In the experiments in which adrenaline, noradrenaline, and pitressin were used, these substances were added to the solution of the convulsant and used at once.Adrenale...