Chronic Lithium Impairs Skin Tolerance to Ischemia in Random-Pattern Skin Flap of Rats

Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Journal of Surgical Research (Impact Factor: 1.94). 11/2011; 171(1):374-8. DOI: 10.1016/j.jss.2010.03.048
Source: PubMed


Despite its apparent anti-apoptotic effect, lithium impairs endothelium-dependent vasorelaxation in various tissues. In this study, we assessed the effect of lithium treatment on ischemic skin flap survival and its interaction with nitric oxide pathway.
Seventy-six male Sprague-Dawley rats were randomly assigned into 13 groups. For skin flap surgery, dorsal skin flap measuring 8 × 2 cm was elevated on the midline. After local injections (if needed), the cranial pedicle was cut and flap was sutured back. Flap survival was assessed after 7 d. Animals in the chronic lithium group received lithium chloride in tap water for 4 wk preoperatively and 7 d postoperatively. Acute lithium groups received 3 nmol, 10 nmol and 3 μmol/flap lithium locally. In another experiment, interaction with nitric oxide synthase inhibitor L-NAME as well as nitric oxide precursor L-arginine was studied, and the effect of ischemic preconditioning on skin flap survival in lithium treated rats was investigated.
Chronic lithium group had mean flap survival value of 32.6% ± 5.2% (mean ± SD), which was significantly lower than normal subjects (52.7% ± 6.1%, P < 0.001), while acute local lithium treatment had no effect. In chronic lithium group, systemic L-NAME (10 mg/kg, 30 min before flap elevation) failed to significantly decrease the survival, while sub-effective systemic L-arginine (100 mg/kg) and ischemic preconditioning significantly increased flap survival (P < 0.001 and P < 0.01, respectively).
We conclude that long-term lithium treatment impairs the skin tolerance to ischemia in rats, which seems to be nitric oxide mediated. This effect is prevented by ischemic preconditioning or L-arginine treatment. The results suggest that skin-involving interventions should be applied more cautiously in patients who are on lithium treatment.

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    • "A cascade of intracellular events happens after skin flap elevation, which is assumed to be responsible for aforementioned ischemia and necrosis. In random pattern skin flap, a phase of vasoconstriction follows flap elevation, especially in the first 6– 12 h which in turn leads to tissue ischemia and hypoxia (Nezami et al., 2011). Following ischemia, the intracellular pH is decreased due to anaerobic glycolysis. "
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    ABSTRACT: Necrosis of distal portion of skin flaps due to ischemia still remains a problem in plastic surgery. Following ischemia, a cascade of deleterious events including over-activity of Na(+)-H(+) Exchanger (NHE) takes place. In present study we evaluated the effect of the potent NHE inhibitor, 5-(N-ethyl-N-isopropyl) amiloride (EIPA) on ischemic tissue injury in a skin flap model, and investigated the role of mitochondrial ATP-sensitive K(+) channels (K(ATP)) in this phenomenon. Seventy-eight rats were randomly divided into thirteen treatment groups (6 rats each). Four groups received different doses of EIPA in the flap. EIPA/GLY group received an effective dose of a K(ATP) channel blocker, glibenclamide (GLY, 0.3mg/kg) intraperitoneally (i.p.) 30min before raising the flap, and a local effective dose of EIPA (0.1mM) immediately after raising the flap. EIPA/diazoxide group (EIPA/DIA) received a sub-effective dose of diazoxide (7.5mg/kg i.p.) 30min before raising the flap and a local sub-effective dose of EIPA (0.075mM). EIPA 0.1 and 0.2mM significantly increased flap survival area compared to control group (56.01±6.1%, P<0.001). The protective effect of EIPA (0.1mM) was abolished by administration of glibenclamide (0.3mg/kg i.p.). Co-administration of a sub-effective dose of EIPA (0.075mM), with a sub-effective dose of diazoxide (7.5mg/kg i.p.) significantly improved flap survival (P<0.05). We demonstrated that the NHE inhibitor, EIPA can increase random pattern skin flap survival. Administration of diazoxide potentiates this effect, while glibenclamide abolishes that, implicating that the protective effect of EIPA is mediated through mitochondrial-K(ATP) channels.
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    ABSTRACT: Background: Metformin has shown cardioprotective effects in experimental models of ischemia reperfusion, which is partially mediated through nitric oxide (NO) synthesis. We investigated the effects of metformin pretreatment in a rat model of random-pattern skin flap, and the probable role of NO system. Materials and methods: In the first experiment, the rats received increasing doses of metformin (150, 200, and 300 mg/kg), 4 h before the procedure. Dorsal skin flaps with caudal pedicles were elevated at the midline and flap survival was measured 7 d after surgery. Pathologic review of the skin flap specimen was performed in a subset of animals. In the second experiment, for evaluation of the role of NO, an NO synthase inhibitor N-nitro-L-arginine methyl ester hydrochloride (L-NAME) was administered with and without the effective dose of metformin. In the next experiment, subtherapeutic dose of NO precursor, L-Arginine, was administered with and without subeffective dose of metformin. Results: Metformin pretreatment at doses of 200 and 300 mg/kg significantly increased skin flap survival rate. However, administration of L-NAME abolished the protective effects of metformin. On the other hand, subtherapeutic dose of L-arginine augmented the effects of low-dose metformin and significantly increased skin flap survival. Skin flaps from those rats that received 300 mg/kg metformin pretreatment and those treated with subtherapeutic doses of L-arginine and metformin showed increased vasodilation compared with control group. Conclusions: Metformin pretreatment can improve skin flap survival through an NO dependent pathway.
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