The actions of hydroxydione sodium succinate (" Viadril ") have been studied in chloralose or decerebrate cats, or cats otherwise untreated. It is virtually devoid of action at the neuromuscular, ganglionic, or peripheral adrenergic synapse. After rapid intravenous injection, hydroxydione produced a transient hypotension with little bradycardia and stimulated the respiration. These effects were over in 1 to 2 min. and were reduced if injection was slow or the hydroxydione diluted. Vagotomy did not alter the depressor response, but reduced the respiratory stimulation. In the untreated or the decerebrate animal, as much as five times the anaesthetic dose of hydroxydione was required to depress the respiration or blood pressure. Chloralose potentiated these depressant actions 5 to 10 fold. Both the circulatory and the respiratory depression appeared to be mediated centrally. Decerebrate rigidity was readily lessened by hydroxydione, but the pinna reflex and conjunctival reflex were relatively resistant to its action, and the knee jerk outstandingly so.Fine transient muscular fasciculations, not unlike those produced by suxamethonium, have occasionally been observed by one of us during hydroxydione administration in man, occurring shortly after the onset of unconsciousness. They appear first in the muscles of the face, spread to the upper limbs and trunk, and die away after a few seconds. Such an observation suggested that hydroxydione might have some neuromuscular action. The possibility became more important in the light of the relaxation which hydroxydione anaesthesia can produce, especially in the pharynx and the larynx. The experiments described below started, therefore, with an investigation, in cats under chloralose, of the neuromuscular action of the drug. cannula in one carotid artery. The respiration was recorded, after a tracheal cannula had been inserted, by the aid of respiratory valves and a respiration recorder on the expiratory side (Paton, 1949). When required, the twitches of the tibialis anterior muscle were recorded on the smoked drum with a steel spring myograph, in response to supramaximal excitation of the sciatic nerve through shielded electrodes in the thigh. Rectangular pulses of 0.5 m.sec. duration were delivered at varied frequencies, usually one every 10 sec. Action on an autonomic ganglion was tested by recording the contractions of the nictitating membrane with a lever of magnification about 5-fold and load about 2 g. writing frontally on the smoked drum, the membrane being excited to contraction by supramaximal preganglionic shocks through the cervical sympathetic nerve in the neck which had previously been separated from the vagus and divided from its central connexions. The contents of the eyeball were removed. Rectangular pulses of 0.5 m.sec. duration were applied, at 10 shocks per sec. either for a period of 15 sec. every min. or continuously, through platinum electrodes. To make injections a venous cannula was inserted into the femoral or jugular veins, and all injections were w...
