The effect of pulsed radiofrequency current on mechanical allodynia induced with resiniferatoxin in rats.

BACKGROUND: Pulsed radiofrequency (PRF) is a popular pain treatment modality. The effect of PRF current on neuropathic pain has not been examined in detail. We investigated the effect of PRF current on mechanical allodynia induced with resiniferatoxin (RTX) in rats, especially regarding the influence of the duration of allodynia before PRF procedures and that of exposure time to PRF. METHODS: Adult male Sprague-Dawley rats (weighing 250-400 g) received a single intraperitoneal injection of RTX (200 microg/kg) under 2 to 3% sevoflurane anesthesia. Rats in group S(2) (n = 5) were assigned to receive PRF current to the right sciatic nerve for 2 minutes 1 week after RTX treatment; rats in group M(2) (n = 6), PRF current for 2 minutes 3 weeks after RTX treatment; rats in group L(2) (n = 7), PRF current for 2 minutes 5 weeks after RTX treatment; rats in group S(4) (n = 5), PRF current for 4 minutes 1 week after RTX treatment; rats in group S(6) (n = 5), PRF current for 6 minutes 1 week after RTX treatment; and rats in group S(0) (n = 3), no PRF current was delivered. Instead, the needle and electrode were inserted at proper points for 6 minutes 1 week after RTX treatment. All rats were evaluated for sensitivity to mechanical stimulation with von Frey filaments and to thermal stimulation with a thermal testing apparatus and for motor function using placing and grasping reflexes before injection of RTX, every week after injection of RTX, and 1, 2, 3, 4, and 5 weeks after PRF treatment. RESULTS: The paw withdrawal thresholds of both hindpaws 1 week after RTX treatment were significantly lower than the pre-RTX baseline in all groups. In groups S(2), S(4), S(6), and M(2), after PRF procedures, the ipsilateral paw withdrawal thresholds significantly increased. A statistically significant difference was detected between the PRF-treated and PRF-untreated hindpaws. The ipsilateral-contralateral paw withdrawal thresholds after PRF procedures in group S(2) were significantly higher than those in groups M(2) and L(2). Between groups M(2) and L(2), significant differences were found 1, 2, 4, and 5 weeks after PRF procedures. The ipsilateral-contralateral paw withdrawal thresholds in group S(6) were significantly higher than those in groups S(2) and S(4) 5 weeks after PRF procedures. No significant difference was found between groups S(2) and S(4) at any time. After PRF procedures, no difference in the withdrawal latency after heat stimulation and no motor disturbance were observed at any time in all groups. CONCLUSIONS: PRF treatment was more effective when applied in the early stages of mechanical allodynia (1 week) in rats. Increased exposure time to PRF current from 2 to 6 minutes showed a significant antiallodynic effect without motor impairment. We propose the application of PRF current for 6 minutes adjacent to the nerve as soon as possible when allodynia appears.

[Epidural infusion of low dose bupivacaine after combined spinal-epidural anesthesia using needle through needle method provided no analgesic effect on postoperative pain after caesarian section].

BACKGROUND: In order to evaluate the analgesic efficacy of low dose epidural bupivacaine infusion with and without morphine after caesarean section we performed combined spinal-epidural anesthesia (CSEA) using needle through needle method. Three different epidural analgesic regimens were compared retrospectively. METHODS: The number of analgesic use during 24 hours after operation was compared. Patients were categorized into three groups; group N : intraoperative bolus epidural morphine (2.5 mg) alone, group L : bolus morphine (2.5 mg) plus epidural bupivacaine infusion (32 ml of 0.2% bupivacaine) at a rate of 2.1 ml x hr(-1), group M : bolus morphine (2.4 mg) plus epidural bupivacaine-morphine (33 ml of 0.2% bupivacaine containing morphine 2.3 mg) infusion at a rate of 2.1 ml x hr(-1). Used analgesics included pentazocine 15 mg i.m., diclofenac 25 mg suppo. and loxoprofen 60 mg p.o.. RESULTS: The mean number of analgesic use during the first 24 hours in group M (0.29 +/- 0.46) was significantly smaller than those of group N (0.97 +/- 0.91) and group L (0.84 +/- 0.95). Percentage of patients requiring no analgesic during the first 24 hours was significantly less in group M (70.8%) than in group N (33.4%) and group L (42.1%). CONCLUSIONS: A 2.1 ml x hr(-1) infusion of epidural bupivacaine has no analgesic effect after caesarean section under CSEA using NTN method.

[Glucose attenuating local anesthetic-induced hemolysis].

BACKGROUND: The effect of glucose on local anesthetic-induced neural damage has not been fully studied. We examined the effect of glucose on hemolysis induced by local anesthetics. METHODS: The mean EC50 values (the local anesthetic level that causes destruction of half of the red blood cells in vitro) of lidocaine HCl, tetracaine HCl and dibucaine HCl were determined with 0% and 7.5% glucose contained in Krebs solution at pH 6.4. RESULTS: The mean EC50 values of lidocaine HCl, tetracaine HCl, and dibucaine HCl in 0%-glucose Krebs solution were 6.51%, 0.45%, 0.17%, respectively, which increased significantly to 7.05%, 0.64% and 0.23%, in 7.5% glucose Krebs solution at pH 6.4. CONCLUSIONS: Glucose may have a protective role in local anesthetic-induced neural damage.

[Ionic strength influences hemolytic action of dibucaine hydrochloride].

BACKGROUND: Little is known about effect of ionic strength on local anesthetic toxicity. Using human erythrocytes, hemolytic action of dibucaine in solutions of various ionic strength was investigated. METHODS: The critical micellar concentration (CMC) of dibucaine and the dibucaine level that causes destruction of half of the red blood cells in vitro (EC50 value) were determined in solutions of various ionic strength. RESULTS: The mean CMC values of the dibucaine solutions adjusted to ionic strength 0.15, 0.30, 0.45 and 0.90 with NaCl, were 35.3, 22.6, 15.9 and 9.6 mM, respectively. The mean EC50 values of these solutions measured at 5 sec were 22.5, 16.0, 12.6 and 8.2 mM, respectively, and those at 30 min were 4.9, 4.5, 4.5 and 2.6 mM, respectively. There was a significant correlation between mean CMC values and mean EC50 values at 5 sec but not at 30 min in the solution of the same ionic strength. CONCLUSIONS: These findings indicated that the mechanism of dibucaine-induced hemolysis within a few seconds is through membrane lysis, whereas dibucaine-induced hemolysis at 30 min is caused by another mechanism. Because each mechanism is enhanced by high ionic strength, dibucaine dissolved in salt solution should not be administered intrathecally.

Increased adrenomedullin concentration in cerebrospinal fluid in patients with septic shock.

Plasma level of adrenomedullin (AM), a potent vasodilator peptide, is increased in patients with sepsis. AM was also found to be present in cerebrospinal fluid (CSF) of humans, and intracerebroventricular injection of AM resulted in elevated systemic blood pressure in rats. In the present study, we measured AM levels in CSF and plasma of 7 patients with septic shock who had severe hypotension, and compared with those of 10 control patients receiving primary transurethral resection of bladder tumor. CSF samples were obtained through the procedure of lumbar puncture and AM levels were measured by radioimmunoassay. AM concentration in CSF of the septic patients was increased to a level 35 times higher than that of control group (35 +/- 21 vs. 0.9 +/-0 .3 pmol/L, mean +/- S .D., p < 0.01). Similarly, plasma AM concentration was increased by 27 times compared with control group (176 +/- 71 vs. 6.5+/-1.8 pmol/L, p < 0.01). Despite the similar increase in CSF and plasma AM, no significant correlation was found between the AM concentrations in the CSF and plasma (r = 0.01 P = 0.95). Taken together with the central actions of AM, these findings suggest that AM of the central nervous system may be involved in pathophysiology of sepsis of humans.

Endomorphins suppress nociception-induced c-Fos and Zif/268 expression in the rat spinal dorsal horn.

We evaluated the potency of endomorphin-1 and -2 as endogenous ligands on c-Fos and Zif/268 expression in the spinal dorsal horn by formalin injection to the rat hind paw. Endomorphin-1, -2, or morphine was administered intrathecally or intracerebroventricularly 5 min before formalin injection (5%, 100 microl). All drugs produced marked reductions of formalin-induced c-Fos and Zif/268 immunoreactivity in laminae I and II, and laminae V and VI in the rat lumbar spinal cord. The reductions of Zif/268 expression by endomorphins were greater than those by morphine, while the reductions of c-Fos expression by endomorphins were smaller than those by morphine. These effects of endomorphins were attenuated by pretreatment with naloxone. These results indicate that endomorphin-1 and -2 act as endogenous ligands of mu-opioid receptor in neurons of the spinal dorsal horn and suppress the processing of nociceptive information in the central nervous system.