Effects of local anesthetics on experiential, physiologic and endocrine measures in healthy humans and on rat hypothalamic corticotropin-releasing hormone release in vitro: Clinical and psychobiologic implications

Local anesthetics, given i.v. to treat cardiac arrhythmias and for regional anesthesia, exert prominent central nervous system side effects, such as sensory distortions and mood changes. In experimental animals, these drugs activate limbic structures, such as the amygdala, that may coordinately regulate sensory processing, mood and pituitary hormone secretion during stress. Clinically relevant i.v. doses of the short-acting local anesthetic procaine were administered to 17 healthy volunteers and topographic electroencephalographic (EEG) spectra, stress-responsive neuroendocrine and cardiovascular parameters and sensory-cognitive and mood changes were examined. Because corticotropin-releasing hormone (CRH) mimics the behavioral and physiologic responses to stress and activates limbic structures in experimental animals, the effects of procaine and lidocaine on immunoreactive CRH release from rat hypothalami in vitro were also explored. Procaine administration produced a dose-related increase in fast (21-50 Hz) EEG activity, a significant decrease in alpha EEG activity and dose-dependent increases in heart rate, systolic blood pressure and plasma adrenocorticotropic hormone, cortisol and prolactin secretion. Dose-dependent increases in sensory distortions involved virtually all modalities, particularly auditory, visual and somatosensory. Mood changes occurred in most subjects, including anxiety, euphoria and arousal. In vitro, procaine and lidocaine both produced significant dose-related increases in immunoreactive CRH release from rat hypothalami, maximal at 10^-6 M, that were blocked by carbamazepine, a limbic anticonvulsant used in the management of mood disorders. The electrophysiologic effects of procaine in these volunteers were analogous to local anesthetic effects in experimental animals and consistent with the activation of subcortical structures localized within the temporal lobe, such as the amygdala. The effects of procaine on stress- responsive neurohormones were similar to those of amygdala stimulation both in experimental animals and human subjects. The in vitro data suggested that procaine-induced pituitary-adrenal activation involves stimulation of hypothalamic CRH, although additional (e.g., limbic-hypothalamic) mechanisms may contribute in vivo. These data were compatible with a direct action of local anesthetics on limbic structures that might account for many of the central effects seen with the systemic use of these agents in clinical practice.