Ryozo Okamoto

Nifedipine-suppressed atherosclerosis in cholesterol-fed rabbits but not in Watanabe heritable hyperlipidemic rabbits

We studied the effects of nifedipine, a calcium antagonist, on atherosclerosis in cholesterol-fed rabbits and Watanabe heritable hyperlipidemic rabbits (WHHL rabbits). Japanese White rabbits were fed 120g of 2% cholesterol rabbit chow daily, and WHHL rabbits were fed standard rabbit chow. In each experiment, the rabbits were divided into two groups. Twenty milligrams of nifedipine was given orally twice a day to the nifedipine group, and the control group was given a placebo in the same way. The rabbits were sacrificed at the end of the 12th week in the case of cholesterol-fed rabbits, and the 20th week in the case of WHHL rabbits. Among the cholesterol-fed rabbits, the percentage of aortic intimal surface area covered by atherosclerotic lesions (AS%) was 25.9 +/- 7.6% (mean +/- S.D.) in the nifedipine group (n = 7), and 55.6 +/- 22.8% in the placebo group (n = 8) (p less than 0.01). The cholesterol content of thoracic and abdominal aorta in the nifedipine group was lower than those in the placebo group (p less than 0.05). Among the WHHL rabbits, the AS% was 33.4 +/- 14.1% in the nifedipine group (n = 5), and 27.0 +/- 11.7% in the placebo group (n =6) (n.s.). The aortic cholesterol and calcium contents also showed no significant differences between the two groups. We concluded that nifedipine suppressed atherosclerosis in cholesterol-fed rabbits but not in WHHL rabbits. The different responses suggest that the effect of nifedipine could be mediated by low density lipoprotein receptors or that the early exposure to hyperlipidemic serum from birth might affect cell functions of WHHL rabbits.

The effect of oxygen on the development of atherosclerosis in WHHL rabbits

The effect of hyperoxic or hypoxic inhalation on blood lipid levels and on the development of atherosclerosis was studied in young male WHHL rabbits. They were exposed to ordinary room air containing different concentrations of oxygen: 6 animals were exposed to 40% oxygen (hyperoxia group) or 5-10% oxygen (hypoxia group) for 5 h a day, 5 days a week for 8 weeks. Four control rabbits inhaled ordinary room air. The following results were obtained. (1) The severity of aortic lesions significantly decreased in the hyperoxia group and increased in the hypoxia group, when these two groups were compared. However, both hypoxic and hyperoxic groups did not statistically differ from the control. (2) Plasma cholesterol levels were not changed either by hyperoxic or hypoxic inhalation. (3) Plasma triglyceride levels were elevated only in the hypoxia group, with significant differences from the values in both control and hyperoxia groups. (4) There was no significant correlation between mean plasma lipid level and severity of aortic lesions. From these results, we conclude that hyperoxic or hypoxic inhalation respectively regresses or aggravates the development of atherosclerotic lesions, not by an indirect action on blood lipid concentrations but by a direct action on the vascular wall.

GENERALIZED SARCOIDOSIS WITH “SARCOID AORTITIS”

A 52‐year‐old man with a clinical diagnosis of aortitis and heart failure died of brain thrombosis. Autopsy revealed many non‐caseous sarcoid granulomas scattered in lymph nodes, lungs, heart, testes, liver, and meninges. An unusual finding of this case was the presence of sarcoid lesions in abdominal aorta and subclavian and common iliac arteries.

Effect of hypoxia on cholesterol accumulation in cultured rabbit aortic smooth muscle cells

We studied the effect of hypoxia on cholesterol accumulation in cultured rabbit aortic smooth muscle cells, which were incubated in a medium with normolipemic rabbit serum (NRS) or hyperlipemic rabbit serum (HRS). The cells were incubated in a humidified atmosphere of either 20% O2, 75% N2 and 5% CO2 (control cells) or 2% O2, 93% N2 and 5% CO2 (hypoxic cells). In a medium containing 20% NRS, the free cholesterol level of hypoxic cells was only a little higher than that of control cells, and there was no significant difference in esterified cholesterol content. On the other hand, in a medium containing 20% HRS, the free cholesterol level was slightly higher and the esterified cholesterol level was markedly higher in hypoxic cells compared with control cells. These results show that hypoxia promotes the accumulation of cholesterol, especially as ester, in smooth muscle cells cultured with hyperlipemic serum. These in vitro experiments indicate that hypoxia in the arterial wall associated with hyperlipidemia may play an important role in atherogenesis, although the precise mechanism remains unclear.

Effect of Tissue Hypoxia on the Development of Atherosclerosis

It has been suggested that hypoxia enhances the development of atherosclerosis. The aim of this study was to clarify the mechanisms. Experiments were designed to observe the effects of hypoxic and hyperoxic inhalation in WHHL rabbits and have revealed that atherosclerotic lesions in the hypoxia group were larger than those in the hyperoxia group. Since there was no fluctuation in plasma cholesterol level, the effect of hypoxia was probably a direct one. Cell culture studies were carried out, using rabbit aortic smooth muscle cells and fibroblasts, and the cells were incubated in the medium supplemented with hyperlipidemic serum. The esterified cholesterol contents in the cells under the hypoxic condition were 2–3 times higher than those under control conditions. Analysis of cholesterol metabolism revealed that hypoxia increased ACAT activity and suppressed cholesterol efflux.

Studies on the Mechanism of Postalimentary Lipemia in Atherosclerosis

Present studies have been undertaken to make observations on the possible correlation between heparin and LPL activity from the viewpoint of the mechanism for disposing ability of alimentary lipemia. In vitro study has revealed the fact that releasing of LPL from the rats tissue was responsible to the biochemical action of heparin. Following the intraarterial or intravenous infusion of heparin, LPL seemed to be released rapidly, suggesting that LPL may be mobilized from the vascular wall or adjacent tissues. No difference of plasma LPL activity after heparin injection in the fasting state between young healthy persons and patients with atherosclerosis was found. Moreover no difference could be observed between the effect of heparin injection on the changes of plasma OD and LPL activities following fat intake in the controls and patients. An assumption was made that deficiency of apoenzyme could not be considered for the interpretation of disturbance in disposing ability of absorbed fat. Heparin-like substance in plasma was measured in the groups on fasting and postalimentary state. Plasma contents of heparin-like substance on fasting are found to be lower on the patients than the controls. One hour increase after fat intake failed to occur in the former, contrary to the latter, thus it is assumed that with the atherosclerotic patients the deficiency of heparin with disturbed releasing biochemical process are the responsible factor concerned. Further, the disturbed disposing ability of NEFA from blood stream is another factor to be considered in the abnormal metabolic process following fat absorption.