Stress-induced lidocaine modification in serum and tissues.

The aim of this study is to examine the influence of acute (trauma) and chronic (cold swimming and adjuvant rheumatoid arthritis) stress on lidocaine concentrations in plasma. Forty male Wistar rats were used. The animals were divided into four groups. Group A served as control. Group B underwent mandible osteotomy. Group C was submitted to swimming stress in cold water 4 degrees C for ten minutes daily for 15 minutes, while group D underwent experimental arthritis with Freud's adjuvant. All groups received lidocaine i.m (2.5 mg/kg). Blood samples were collected and FFA (free fatty acid), unbound-lidocaine, albumin and a1-acid glycoprotein concentrations were estimated. Furthermore, the adrenals, heart and liver were isolated. The adrenals' relative weight (adrenal weight/body weight) was assessed, while lidocaine concentrations in the heart and the liver incubation medium were measured by intertechnic a-counter. Lidocaine and FFA levels in serum as well as the adrenal weights demonstrated a significant elevation in stress-groups as compared to the control group. Furthermore, in the stress-groups, lidocaine concentrations in heart tissue were significantly increased, whereas in the liver they were significantly reduced as compared to the control group. Our results indicate that stress can alter lidocaine levels in plasma and tissues, suggesting that stress should be considered an important factor when determining the dosage of lidocaine in clinical application.