Abstract
This study was designed to examine the erects of regression on contractile and relaxation responses to vasoactive agents in atherosclerotic rabbit aortas. Twenty-eight male rabbits were separated into four groups as follows: Group (G) I was fed a normal diet for 16 weeks, GII was fed a 1% cholesterol diet for 16 weeks, GIII was fed a 1% cholesterol diet for 16 weeks followed by a normal diet for 16 weeks, GIV was fed a normal diet containing 0.5% probucol for 16 weeks after induction of atherosclerosis as GII. Thoracic) aortas were cut into ring preparations and suspended in an organ bath containing Krebs-Ringer solution. Isometric tensions generated by KCl, histamine (His), norepinephrine (NE) were recorded and the relaxation response to acetylcholine (ACh) was also examined.
The percentile area of atheromatous plaque was 0.91±6, 51±10, 44±6 (mean±SE) respectively in the four groups. The maximum tension developed by KCl was approximately the same in all four groups. The maximum tension generated by His and NE was lower in GII and GIII than in GI, although the same tension was maintained in GIV as in GI.
The maximum relaxation response induced by ACh was 42±6, 14±3, 1.5±0.9, 2.3±1.5, respectively in the four groups when the tension generated by 10-6 M PGF2α was defined as 100%.
ED50 under KCl was lower in GIII than in the other three groups. ED50 under NE was greater in GII and GIII than in GI. ED50 under His was the same for all four broups. T 1/2 was increased and dT/dt was reduced in atherosclerotic aortas (GII), and regression was not improved.
Regressed aortas caused by probucol showed recovery of contractile responses to His and NE, but not by a normal diet. The relaxation response to ACh, T 1/2 and dT/dt in regressed aortas-(GIII and IV) were not improved.
