Abstract
The purpose of this study was to determine if the calcium entry antagonist felodipine inhibited intimal lesion formation in hypercholesterolemic rabbits, and to determine if this was due to an effect upon monocyte and/or endothelial determinants of this interaction. Twenty-three male New Zealand White rabbits received the following treatment regimen for 10 weeks: normal chow (NP, n = 3); normal chow with felodipine infusion (NF, n=6); 0.5% cholesterol chow (CP, n = 7); or 0.5% cholesterol chow and felodipine infusion (CF, n=7). After 10 weeks blood was collected for biochemical measurements and mononuclear cell binding assays, and thoracic aortae were harvested for vascular reactivity studies and histomorphometry.
In the animals receiving normal chow, felodipine did not significantly affect blood pressure, plasma cholesterol levels, binding studies, vascular reactivity, or structure; therefore these animals were analyzed as one group (N). Plasma cholesterol levels were significantly elevated in groups receiving the 0.5% cholesterol diet (N, 29±3 mg/dl; CP, 1221±73 mg/dl; CF, 979±108 mg/dl). High-density lipoprotein cholesterol was not different between the groups (25±4 vs 23±4 vs 27±4 mg/dl; N vs CF vs CP respectively; p=NS). Cholesterol feeding markedly augmented the adhesiveness of mononuclear cells, as demonstrated by a 250% increase in cell binding. Felodipine did not alter the adhesiveness of mononuclear cells in hypercholesterolemic animals. Cholesterol feeding significantly impaired endothelium-dependent relaxations. Endothelium-dependent relaxations were restored by felodipine treatment as reflected by the maximal responses to acetylcholine (40±7% vs 58±4% vs 67±5%; CP vs CF vs N respectively). The improvement in endothelium-dependent relaxation in the felodipine-treated animals was associated with a 2.2-fold reduction in lesion surface area of the thoracic aorta (8.2±6.3% vs 18.2±9.5%; CF vs CP; p<0.01). Moreover, the intima/media ratio reflecting lesion thickness was substantially reduced by felodipine treatment (0.05±0.02 vs 0.20±0.07; CF vs CP; p=0.006). Ex vivo studies revealed that felodipine inhibited the adhesiveness of vascular endothelium, but not mononuclear cells, derived from hypercholesterolemic animals.
Low-dose felodipine appears to inhibit monocyte-endothelial interaction, as indicated by a reduction in the formation of lesions in hypercholesterolemic animals. This effect is not due to an alteration in adhesiveness of mononuclear cells. The salutary effect of felodipine is associated with an increase in vascular nitric oxide activity which may reduce endothelial adhesiveness.