Effects of midazolam on the contraction and relaxation of segments of thoracic aorta stripped of endothelium and stimulated by adrenaline--experimental study in rabbits.

To evaluate the effects of midazolam on the angiokinesis of segments of rabbits' thoracic aorta stripped of endothelium and stimulated by adrenaline. Two groups of aortic rings removed from albinic rabbits anesthetized with thiopental were used (Group I-6 animals; Group II-12 animals), stripped of endothelium, studied in an organ chamber, perfused by Krebs-Henseleit solution. The groups were stimulated by adrenaline, recording the maximum contraction and dT/dt at 12", 36", 60" and 120". When the plateau phase was reached, the vessel was washed with perfusion solution, recording relaxation at 2', 4' and 6'. When the base values were reached, Group I underwent a new adrenergic stimulus; and Group II was stimulated with midazolam and then with adrenaline, and the same values were recorded. T test was applied as a statistical analysis when two variables were studied. When studying more than two variables the Anova test was used, supplemented by the Tuckey test. Group I did not show any significant difference between the two stimuli. Group II--the midazolam significantly reduced the maximum contraction induced by adrenaline (83.01 +/- 4.11%) (p < 0.01). The dT/dt was reduced at 12" (57.06 +/- 8.47%), and also at 36" (70.59 +/- 5.26%). There was no significance at 60" and 120" (p < 0.01). The relaxation increased significantly at all measurements--at 2'-adrenaline 39.31 +/- 9.60%; adrenaline/midazolam: 44.06 +/- 9.62% (p < 0.05). At 4'-adrenaline: 53.08 +/- 8.3%; adrenaline/midazolam: 61.68 +/- 8.50% (p < 0.01). At 6'-adrenaline: 76.26 +/- 5.45%; adrenaline/midazolam: 84.20 +/- 7.96% (p < 0.01). Midazolam significantly reduced the maximum contraction obtained by the adrenergic stimulus as well as the dT/dt in the initial phases of contraction. The relaxation speed also increased.