Physiological and behavioral effects of naloxone and lactate in normal volunteers with relevance to the pathophysiology of panic disorder.

This study investigates whether naloxone, an opioid receptor antagonist, could render normal controls, normally nonresponsive to panic inducing stimuli, sensitive to the physiological and behavioral effects of sodium lactate, a robust panicogen in panic disorder patients. Twelve normal controls received intravenous naloxone followed by sodium lactate. Four of these subjects underwent a separate infusion with naloxone followed by saline. Respiratory physiological symptoms were measured throughout. Clinical symptoms, assessed by the Acute Panic Inventory (API), an Anxiety Scale, and the Borg Breathlessness Scale, were recorded. Eight of the twelve subjects experienced strong physiological reactivity to naloxone-lactate manifested by significantly increased tidal volume. Concomitant increases in the API and Borg scales were demonstrated; however, fear or anxiety was not affected. The four subjects retested with naloxone followed by saline did not experience significant increases on any measure. These results provide preliminary evidence that endogenous opioid system function may be a key modulator of responsivity to sodium lactate. Dysregulation of the opioid system may potentially underlie critical aspects of panic disorder neurobiology, including respiratory abnormalities and suffocation sensitivity.