1. Pitts and McClure reported that anxiety attacks could be produced in anxious patients by the infusion of sodium lactate, and they formulated a new theory to explain how this was achieved. To test their findings, 20 patients suffering from anxiety neurosis and 10 normal controls were given an intravenous infusion of saline followed by one of sodium lactate, and 12 minutes after the infusion ended they were stressed by mental arithmetic. Throughout the procedure, psychological and physiological arousal were monitored by observer and self-ratings of anxiety, forearm blood flow and heart rate. All these measures increased significantly when the intravenous cannula was inserted.
2. Eighty-five per cent of the patients experienced an anxiety attack during or after the sodium lactate infusion, as compared with only 5 per cent during normal saline. The number of anxiety symptoms and mean observer and self-ratings of anxiety, forearm blood flow and heart rate were higher during the lactate than during the saline infusion.
3. The maximum anxiety produced in the patients by sodium lactate, as measured by these variables, was significantly greater than that produced by the insertion of the intravenous cannula.
4. None of the controls experienced an anxiety attack during the saline infusion, as compared with 10 per cent during lactate.
5. Lactate produced more symptoms, and these started sooner in patients than in controls, and the number of symptoms per subject and number of anxiety attacks produced in our study were similar to those reported by Pitts and McClure.
6. Sodium lactate provides a biochemical means of producing anxiety in the laboratory which may prove to be useful for testing the anti-anxiety effect of various types of treatment. Eight patients who had experienced lactate-induced anxiety attacks were subsequently treated with M.A.O.I. antidepressants; those who responded well clinically experienced fewer symptoms during a repeat lactate infusion.
7. The Pitts and McClure hypothesis for explaining the relationship between anxiety and sodium lactate may not be correct, but more information about the biochemical changes involved may further our understanding of the aetiology and treatment of anxiety.