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.

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.