Effect of melatonin on vascular reactivity in vitro after subtotal pancreatectomy in Wistar rats

REYES-TOSO, C.F., LINARES L.M, RICCI C., ARÁN M., ALBORNOZ, L., PLANELLS, F., RODRIGUEZ R.R., CARDINALI D.P.

Tandil, Argentina.

Congreso; ARGENTINIAN ASSOCIATION OF EXPERIMENTAL PHARMACOLOGY. XXXIV ANNUAL MEETING; 2002

ARGENTINIAN ASSOCIATION OF EXPERIMENTAL PHARMACOLOGY

Pancreatectomy (Ppx) is one of the standard procedures in diabetes research. Based on the existence of an alteration in vascular reactivity (VR) in diabetes, the aim of this study was to evaluate the effect of melatonin (Mel) on VR of rats turned intolerant to carbohydrates. Intolerance was obtained by subtotal Ppx. Rings of thoracic aorta were placed in organ chambers, and isometric tension was recorded. Dose response curves to Phenylephrine (PhE) and Acetylcholine (Ach) were performed with and without Mel (10-5 M). The effect of incubating the aortic rings in a Krebs solution with glucose (G) 44mM was also evaluated. PhE response did not differ between groups. Rings pre-treated with G presented a diminished relaxation to Ach as compared to rings incubated with G+Mel: Ach 10-4 (G 24,85±1,70vsG+Mel 7,43± 1,50%p<0.01), 10-5 (G 26,79±1,32vsG+Mel 8,32±1,34% p<0.01), 10-6 (G 36,06±1,92vsG+Mel 17,03±2,59% p<0.001), 10-7 (G 65,75±3,63vsG+Mel 41,48±6,91%p<0.001), 10-8 (G 86,58±2,31 vs. G+Mel 67,15±6,05 p<0.001). These results show that: 1) Ppx rats develop an alteration in vascular response; 2) Mel significantly increased the Ach evoked relaxation of rings incubated with G. Since exposure of vascular tissue to a high glucose medium impairs endothelium-dependent vasodilatation through superoxide anion production, the mechanism of Mel action can be related to the antioxidant properties of Mel.