Nitric oxide modulation affects the tissue distribution and toxicity of bupivacaine

The effect of lipid emulsion on pharmacokinetics and tissue distribution of bupivacaine in rats

BACKGROUND

While lipid emulsion may reverse the systemic toxicity of bupivacaine, the pharmacokinetics and tissue distribution of bupivacaine after lipid emulsion infusion are not clear. In this study, we assessed the influence of lipid emulsion administration on the pharmacokinetics and tissue distribution of bupivacaine.

METHODS

Rats in the lipid group were administered IV bupivacaine at the rate of 2 mg·kg(-1)·min(-1) for 4 minutes, and then were treated with an infusion of 30% lipid emulsion at the rate of 3 mL·kg(-1)·min(-1) for 5 minutes; saline was substituted in the control group (n = 6 for pharmacokinetics). We then randomly assigned 100 rats into the lipid group and control group (n = 50 for distribution). The toxicity model and treatment were the same as the pharmacokinetic portion. Plasma and tissues including brain, heart, liver, spleen, lung, kidney, omentum, and muscle were collected. The plasma concentration and tissue content of bupivacaine were measured by a liquid chromatography-tandem mass spectrometric method. A 2-compartmental analysis was performed to calculate the pharmacokinetics of bupivacaine.

RESULTS

All data are shown as mean ± SD. After treatment with the lipid emulsion, t1/2β of bupivacaine in the lipid group was significantly shorter (110 ± 25 minutes vs 199 ± 38 minutes, P = 0.001), the clearance was higher (14 ± 4 mL·mg(-1)·kg(-1) vs 9 ± 4 mL·mg(-1)·kg(-1), P = 0.038), and the t1/2α was longer than that of the control group (4 ± 1 minutes vs 2 ± 1 minutes, P = 0.014); the K12 in the lipid group was less than that of the control group (0.13 ± 0.04 vs 0.32 ± 0.13, P = 0.011). In the lipid group, the bupivacaine content in heart, brain, lung, kidney, and spleen was lower than that in the control group, but higher in the liver at 20, 30, and 45 minutes.

CONCLUSION

The lipid sink phenomenon was observed in this study. The use of a lipid emulsion accelerated the elimination of bupivacaine.

N-nitro-L-arginine, a nitric oxide synthase inhibitor, aggravates iminodipropionitrile-induced neurobehavioral and vestibular toxicities in rats

Exposure of iminodipropionitrile (IDPN) to rodents produces permanent behavioral syndrome characterized by repetitive head movements, circling and back walking. Other synthetic nitriles of industrial importance such as crotonitrile and allylnitrile are also able to produce similar motor deficits in experimental animals. However, due to the well-defined behavioral deficits and their easy quantification, IDPN-induced behavioral syndrome is a preferential animal model to test the interaction of various agents with synthetic nitriles. This study reports the effect of non-specific nitric oxide synthase inhibitor, N-nitro-L-arginine (NARG) on IDPN-induced neurobehavioral toxicity in adult male Wistar rats. Four groups of animals were given i.p. injections of IDPN (100 mg/kg) for 6 days. These rats were treated with oral administration of NARG in the doses of 0 (IDPN alone group), 50, 150 and 300 mg/kg, 60 min before IDPN, respectively. Control rats received vehicle only, whereas another group was treated with 300 mg/kg of NARG alone (without IDPN). The results showed that NARG significantly exacerbated the incidence and intensity of IDPN-induced dyskinetic head movements, circling and back walking. The histology of inner ear showed massive degeneration of the sensory hair cells in the crista ampullaris of rats receiving the combined treatment with IDPN and NARG, suggesting a possible role of nitric oxide in IDPN-induced neurobehavioral syndrome in rats.