Canadian Journal of Anesthesia, Vol 44, 765-774, Copyright © 1997 by Canadian Anesthesiologists' Society

ARTICLES

Nocifensive reflex thresholds in rats: measures of central nervous system effects of barbiturates

DP Archer, N Samanani and SH Roth
Department of Anaesthesia, University of Calgary, Canada. archerd@cadvision.com

PURPOSE: To characterize the pharmacodynamic relationships between plasma pentobarbitone and thiopentone concentrations and nocifensive reflexes during emergence from anaesthesia. METHODS: Forty-nine rats were studied. Plasma barbiturate concentrations were measured with high performance liquid chromatography. Nocifensive reflexes were assessed with the hindlimb withdrawal latency (WL) to heat and the somatic motor response threshold (SMRT) to tail pressure. In Protocol I, SMRT, WL, sedation, and the presence of paw-licking and the righting reflex were assessed in unrestrained rats before and every 10 min for two hours after an intraperitoneal injection of pentobarbitone (30 mg.kg-1). Plasma pentobarbitone kinetics were determined in a separate group of rats. In Protocol II, SMRT and drug concentrations were measured concurrently in partially restrained animals before and for 35 min after a computer-controlled i.v. bolus of thiopentone. In Protocol III the SMRT-plasma thiopentone relationship was determined during increasing and decreasing plasma thiopentone concentrations. RESULTS: Enhancement of both nocifensive reflexes was observed in the unrestrained animals. Enhancement of SMRT was maximal [175% (153-197) of control values] at a mean plasma thiopentone concentration of 11 (9-13) micrograms.ml-1. The SMRT-plasma thiopentone curve showed a mean efflux-influx difference in plasma thiopentone concentration of 4(2.3-5.7) micrograms.ml-1. CONCLUSIONS: Barbiturate-associated nocifensive reflex enhancement occurs in unrestrained animals with both thermal and pressure stimuli. The SMRT-plasma thiopentone concentration relationship during emergence from anaesthesia was similar to that observed previously during induction. The thiopentone plasma concentration-SMRT plot showed an equilibrium delay similar to that previously described by others for thiopentone at an electroencephalographic effect site.

This article has been cited by other articles:

				D. P. Archer and S. H. Roth Low Concentrations of Pentobarbital Enhance Excitability of Rat Hippocampal Neurons Anesth. Analg., October 1, 2007; 105(4): 993 - 997. [Abstract] [Full Text] [PDF]

				D. P. Archer, Y. Lamberty, B. Wang, M. J. Davis, N. Samanani, and S. H. Roth Levetiracetam Reduces Anesthetic-Induced Hyperalgesia in Rats Anesth. Analg., January 1, 2007; 104(1): 180 - 185. [Abstract] [Full Text] [PDF]

				I. Gilron Review article: The role of anticonvulsant drugs in postoperative pain management: a bench-to-bedside perspective: [Le role des anticonvulsivants dans le traitement de la douleur postoperatoire : perspective d'une application]. Can J Anesth, June 1, 2006; 53(6): 562 - 571. [Abstract] [Full Text] [PDF]

				A. Ewen, R. G. Cox, S. A. Davies, J. B. Luntley, Y. Rubin, G. H. Fick, and B. B. Bart The ankle clonus test is not a clinically useful measure of spinal cord integrity in children: [Le test du clonus du pied n'est pas une mesure cliniquement utile de l'integrite de la moelle epiniere chez les enfants] Can J Anesth, May 1, 2005; 52(5): 524 - 529. [Abstract] [Full Text] [PDF]

				D. P. Archer, N. Samanani, and S. H. Roth Pentobarbital induces nocifensive hyperreflexia, not hyperalgesia in rats Can J Anesth, July 1, 2000; 47(7): 687 - 692. [Abstract] [Full Text] [PDF]