Melatonin improves vascular reactivity of endotoxemia rats

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1 Acta Physiologica Sinica, June 25, 2005, 57 (3): , *,,,, (melatonin, MT) (lipopolysaccharide LPS) LPS LPS+MT MT (phenylephrine PE) (acetylcholine ACh) (malondialhyde MDA) (superoxide dismutes SOD) LPS 6 h PE (P<0.01), PE ( ~ mol/l) ACh (P<0.01) ACh ( ~ mol/l) MT LPS PE LPS LPS+MT PE ACh LPS MT LPS MDA SOD MT Q463; R363.2 Melatonin improves vascular reactivity of endotoxemia rats XING Han-Ying, LING Yi-Ling *, MENG Ai-Hong, ZHAO Xiao-Yun, HUANG Xin-Li Department of Pathophysiology, Hebei Medical University, Shijiazhuang , China Abstract: The purpose of the present study was to investigate the effect of melatonin (MT) on the abnormal reactivity of thoracic aorta and pulmonary artery induced by lipopolysaccharide (LPS) in rats. Sprague-Dawley rats were divided into four groups randomly: (1) Vehicle group; (2) LPS group: LPS (4 mg/kg, i.p.); (3) LPS+MT group: MT (5 mg/ml, i.p.) was given 30 min before LPS and 60 min after LPS (4 mg/kg,i.p); (4) MT group: received two doses of MT, 90 min after the first injection of MT another dose of MT was given. Six hours after LPS injection the rats were killed and both thoracic aortic rings (TARs) and pulmonary artery rings (PARs)were prepared. The reactivity of TARs and PARs in the four subgroups was tested separately. The contraction response to phenylephrine (PE) and the endothelium-dependent relaxation response (EDRR) to ACh were observed with the isolated artery ring technique. Concentration-response curves were generated with ACh or PE ( ~ mol/l). Superoxide dismutes (SOD) activity and the content of malondialhyde (MDA) in artery tissues were detected. For TARs, LPS significantly reduced the contraction response to PE compared with the vehicle group (P<0.01) and the curve of cumulative dose responses to PE in the LPS group shifted downward. Although EDRR to ACh in the LPS group had the tendency to decrease but still showed no significant difference compared with the vehicle group (P>0.05). For PARs, EDRR to ACh was depressed significantly in the LPS group (P<0.01), while no effect on contraction response to PE in the LPS group was observed, compared with the vehicle group (P> 0.05). Compared with the LPS group, TARs in the LPS+MT group exhibited an increased contraction response to PE, but were still lower than that in the vehicle group. Similarly, EDRR to ACh of PARs in the LPS+MT group was improved significantly and there was no difference between the LPS+MT group and the vehicle group.the vascular reactivity was unaffected in MT group compared with the vehicle group in both TARs and PARs. SOD activity Received Accepted * Corresponding author. Tel: ; Fax: ; lingyiling@tom.com

2 368 Acta Physiologica Sinica, June 25, 2005, 57(3): in the LPS +MT group increased significantly and the content of MDA decreased markedly compared with the LPS group. These results suggest that MT may improve the vascular reactivity in endotoxemia rats due to its antioxidant properties. Key words: melatonin; lipopolysaccharides; pulmonary artery; thoracic aorta (melatonin MT) MT MT [1] (lipopolysaccharide LPS) LPS [2,3] MT MT [4-6] MT MT LPS MT LPS ACh Sigma, (phenylephrine PE), (malondialhyde MDA) (superoxide dismutes SOD) 1.2 Sprague- Dawley 230~260 g 12 h 4 (1) (i.p.) (2) LPS LPS 4 mg/kg i.p.; (3) LPS+MT MT 5 mg/kg( 0.5%) i.p. 30 min LPS 4 mg/kg i.p. LPS 60 min MT 5 mg/kg (4) MT MT 5 mg/kg i.p. 90 min MT 5 mg/ kg LPS 6 h MT 5 h MT 8:30~10: (50 mg/ kg i.p.) 4 Krebs-Ringer bicarbonate (KRB) 95% O 2-5%CO 2 (ph 7.2~ 7.4) 3~4 mm (thoracic aortic rings, TARs) 2 mm (pulmonary artery rings PARs) 1 1 ( 80 MDA SOD ) ml KRB KRB mol/l ( ) 15 min 2 g 90 min 15 min 1 g 60 min 15 min (60~ 70 ) mol/l PE KRB (1) mol/l PE (2) mol/l ACh (3) mol/l PE ACh ( ~ mol/l) (4) ~ mol/l PE, KRB g/mg dw PE ( mol/l) 1.5 SOD MDA 80 10% (0.9%

3 : ) r/min 4 5 min SOD MDA 2~3 3~4 1.6 mean ± SD (one way ANOVA) Newman-Kuels q 369 P< LPS LPS 6 h mol/l PE (P<0.01) PE ( ~ mol/l), PE ( mol/l PE Table 1. Contractive response to PE in thoracic aortic rings and pulmonary artery rings from each group Group mol/l PE (g/mg dw) n Thoracic aortic rings n Pulmonary artery rings Vehicle ± ±0.22 LPS ±0.09 ** ±0.16 LPS+MT ±0.08 *## ±0.17 M T ± ±0.19 The rings were from rats treated with vehicle, LPS (4 mg/kg), LPS+MT (5 mg/kg 2) or MT only. mean ± SD. * P<0.05, ** P<0.01 vs vehicle; ## P<0.01 vs LPS mol/l ACh Table 2. Relaxation response to ACh in thoracic aortic rings and pulmonary artery rings from each group mol/l ACh (%) Group n Thoracic aortic rings n Pulmonary artery rings Vehicle ± ±7.38 LPS ± ±12.18 ** LPS+MT ± ±11.80 ## M T ± ±6.03 The relaxation responses were expressed as percentage reduction of mol/l PE-induced initial vascular tension. mean ± SD. ** P<0.01 vs vehicle, ## P<0.01 vs LPS ~ mol/l PE Fig.1. Contraction responses to cumulative doses of PE ( ~ mol/l) in thoracic aortic rings. mean ± SD. * P<0.05 vs vehicle, # P<0.05 vs LPS. 1 1) mol/l ACh (P> ) mol/l ACh (P<0.01) ACh ( ~ mol/l) ( 4); mol/l PE (P>0.05, 1 3) 2.2 MT LPS LPS+MT PE LPS (P<0.01) ( 1) PE LPS ( 1) mol/l ACh LPS (P>0.05) LPS+MT

4 370 Acta Physiologica Sinica, June 25, 2005, 57(3): ~ mol/l ACh Fig. 2. Endothelium-dependent relaxation responses to cumulative doses of ACh ( ~ mol/l) in thoracic aortic rings. The relaxation responses were expressed as percentage reduction of mol/l PE-induced vascular tension. The responses to cumulative doses of ACh in LPS, LPS+MT or MT groups had no significant differences compared with the vehicle groups (P>0.05) ~ mol/l ACh Fig. 4. Endothelium-dependent relaxation responses to cumulative doses of ACh ( ~ mol/l) in pulmonary artery rings. The relaxation responses were expressed as percentage reduction of mol/l PE-induced vascular tension. * P<0.05 vs vehicle, # P<0.05 vs LPS ~ mol/l PE Fig. 3. Contraction responses to cumulative doses of PE ( ~ mol/l) in pulmonary artery rings. The responses to cumulative doses of PE in LPS, LPS+MT or MT groups had no significant differences compared with the vehicle groups (P>0.05) mol/l ACh LPS (P<0.01) ( 2) ~ mol/l ACh LPS ~ mol/l PE LPS ( 3 4) MT PE ACh (P>0.05) 2.3 MDA SOD LPS MDA SOD MT LPS MDA SOD ( 3) 3. MT MDA SOD Table 3. Effect of MT on MDA content and SOD activity in thoracic aorta and pulmonary artery from endotoxemia rats Group MDA (nmol/ml) SOD (U/ml) Thoracic aorta Pulmonary artery Thoracic aorta Pulmonary artery Vehicle 6.84± ± ± ±7.63 LPS 10.21±1.64 ** 13.33±1.08 ** 65.62±10.91 ** 65.63±8.60 * LPS+MT 6.79±1.55 ## 8.18±1.52 ## 79.57±6.66 ## 78.86±4.80 # M T 6.82± ± ± ±11.47 Thoracic aorta and pulmonary artery were from rats treated with vehicle, LPS (4 mg/kg), LPS+MT (5 mg/kg 2) or MT. mean ± SD, n=6. * P<0.05,, ** P<0.01 vs vehicle; # P<0.05, ## P<0.01 vs LPS.

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