Hypercholesterolemia causes both diminished synthesis as well as impaired diffusion of EDRF in rabbit aorta

1811 [ P.th.i68 1

Hyparcholesterolemia causes both diminished synthesis as well as impaired diffusion of EDRF in rabbit aorta Riezebos, J., Vleeming, W., van Rooij, H.H., Wemer, J., de Wildt *, D.J., Speijers *, G.J.A. a n d Porsius, A.J. Dept. of Biomedical Pharmacy, Faculty of Pharmacy, University of Utrecht, Croesestraat 79, 3522 AD Utrecht and * Dept. of Pharmacology, National Institute of Public Health and Environmental Protection, P.O. Box 1, 3720 BA Biithoven, The Netherlands

It has been reported that hypercholesterolemia inhibits endothelium dependent (ED) relaxations to acetylcholine (ACh) and adenosine-tri-phosphate (ATP) in rabbit aorta while the release of EDRF from abdominal aorta is not affected (Verbeuren, 1986). in this study we investigated the effects of 4 and 12 weeks cholesterol feeding on both ED relaxation and EDRF release in rabbit isolated aorta. Two groups of twenty rabbits received the cholesterol enriched (0.3~;) diet or a control diet (100 g/day) for 4 or 12 weeks respectively. Of each group ten rabbits were simultaneously treated with verapamii (2 mg/kg, 2 dd, s.c.).During the experiment, bloc,d was taken to determine several biochemical parameters. After 4 or 12 weeks, the rabbits were sacrificed and 2 cm aortic segments were mounted in oxygenated Krebs buffer in a sandwich technique to measure luminal EDRF release. Circumferential strips of the thoracic aorta adjacent to the aortic segments were used for ED relaxation studies. Using a resting tension of 2.0 g, tension was recorded isometrically. After precontraction of the strips to 60~-80~ of their maximum contraction with phenylephrine, cumulative dose response curves for ATP, ACh and sodium nitroprusside (SNP) were established. At the end of the organ chamber experiments, the donor segments were fixed with formaline (10~) for histological examination, together with the aortic arch and distal thoracic aorta. After 4 weeks of cholesterol feeding, total cholesterol in control (n = 10) and cholesterol fed rabbits ( n - - 1 0 ) averaged 1.95 + 0.32 mmol/l and 37.80 + 7.13 mmol/l respectively. The 12 weeks of cholesterol diet resulted in total cholesterol levels of 1.40 + 0.63 mmol/i in control (n = 9) and 46.33 + 9.58 mmol/! in cholesterol fed rabbits (4 -- 10). Table 1 presents maximal endothelium independent (SNP) and ED relaxations (ACh, ATP) in aortic strips and sandwich preparation after 12 weeks of hypercholesterolemia. These results show, that the diminished EDRF release cannot fully account for the impaired ED relaxations in the hypercholesterolemic rabbit. We conclude that 1) hypercholesterolemia causes an impairment of ACh- and ATP-induced luminal EDRF release and 2) diminished EDRF synthesis as well as impaired abluminal EDRF diffusion may cause inhibition of ED relaxations during experimental atherosclerosis. Table 1 maximal relaxations (~ of precontraction).

SNP (1 pM) ATP (0.3 raM) ACh (1 pM)

Sandwich preparation Control Cholesterol

Aortic strips Control

Cholesterol

96.6 4.1.4~ 55.8 4-5.8~ 65.1 4-4.75

92.2 4-1.9~ 68.1 4-4.1~ 66.0 4-4.5~

86.7 4-2.9~ 42.6 4- 3.7~; * * 35.8 4-5.6% * *

** p < 0.05 Reference Verbeuren, T.J. et al., 1986, Circ. Res. 58, 552-64.

94.6 4-1.4~ 47.2 4-4.5~ 40.2 4-3.77o * *