Total plasma cholesterol

In Western countries, the total plasma cholesterol in humans is about 5.2 mmol/L, rising with age, though there are wide variations between individuals. The greater part is found in the esterified form. It is transported in hpoproteins of the plasma, and the highest proportion of cholesterol is found in the LDL. Dietary cholesterol equifibrates with plasma cholesterol in days... 

Because total cholesterol is composed of cholesterol derived from LDL, VLDL, and HDL, determination of HDL is useful when total plasma cholesterol is elevated. HDL may be elevated by moderate alcohol ingestion (fewer than two drinks per day), physical exercise, smoking cessation, weight loss, oral contraceptives, phenytoin, and terbutaline. HDL may be lowered by smoking, obesity, a sedentary lifestyle, and drugs such as /1-blockers. 

A desirable total plasma cholesterol level is considered to be less than 200 mg/dl. This value corresponds to about 130 mg LDL cholesterol/dl. Values between 200 and 239 mg/dl are classified as borderline high those above 239 mg/dl (190 mg LDL cholesterol/dl) are simply high. Type 11 heterozygotes frequently have plasma cholesterol in the range 400-600 mg/dl, very high indeed. Homozygotes, who... 

Alterations in the composition of the plasma lipids caused by estrogens are characterized by an increase in the high-density lipoproteins (HDL), a slight reduction in the low-density lipoproteins (LDL), and a reduction in total plasma cholesterol levels. Plasma triglyceride levels are increased. Estrogens decrease hepatic oxidation of adipose tissue lipid to ketones and increase synthesis of triglycerides. 

Monounsaturated fats Triacylglycerols containing primarily fatty acids with one double bond are referred to as monounsaturated fat. Unsaturated fatty acids are generally derived from vegetables and fish. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL cholesterol, but increase HDLs. This ability of monounsaturated fats to favorably modify lipoprotein levels may explain, in part, the observation that Mediterranean cultures, with diets rich in olive oil (high in monounsaturated oleic acid), show a low incidence of coronary heart disease. 

Consumption of saturated fats is strongly associated with high levels of total plasma cholesterol and LDL cholesterol. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL cholesterol, but increase HDLs. 

Considerable discussion has arisen in the lay press about cholesterol and its link to cardiovascular disease because of the correlation between elevated levels of cholesterol in the plasma and the incidence of heart disease. Experts generally agree that people who have total plasma cholesterol levels above 240 mg/dl (6.2 mmole/1) for many years are at increased risk of having a heart attack compared with people whose plasma cholesterol level is below 200 mg/dl (5.2 mmole/1). Because of this it is generally recommended that adults should endeavor to achieve levels of total cholesterol (including both free cholesterol and choles-teryl ester) in plasma of 200 mg/dl (5.2 mmole/1) or less. As discussed in the text, plasma cholesterol is largely carried in LDL as cholesteryl ester. The cholesteryl ester carried by LDL is sometimes referred to in the lay press as bad cholesterol. 

In six patients with renal transplants treated with sirolimus, mean total plasma cholesterol, triglyceride, and apolipoprotein concentrations increased (1067). The authors suggested that sirolimus increases lipase activity in adipose tissue and reduces lipoprotein lipase activity, resulting in increased hepatic synthesis of triglycerides, increased secretion of VLDL, and increased hypertriglyceridemia. 

The effect of oral barium exposure on various blood chemistry parameters that are important for cardiovascular function has been evaluated in only one experimental study with humans (Wones et al. 1990). In this study, 0.2 mg barium/kg/day as barium chloride was supplied in the drinking water of subjects for 4 weeks. No clinically significant changes were noted in any of the blood chemistry parameters monitored (total plasma cholesterol plasma triglycerides plasma HDL and LDL cholesterol plasma apolipoproteins and serum glucose, potassium, calcium, and albumin). 

Although most epidemiological studies on the relationships between plasma lipids and coronary heart disease have examined total plasma cholesterol (most of which is apoB-associated cholesterol) as a major risk factor, some case-control studies have shown that apoB-100 (i.e., apoB in LDL and VLDL) is higher in subjects with coronary heart disease than controls (A31, A32, F2, M34, 06, RIO, S43, V6, W14). It may be that apoB is itself a risk factor, and that a raised apoB concentration but normal LDL cholesterol will be a marker for a previously unsuspected group of people at risk from coronary heart disease (S43). An increasing body of evidence suggests that hyper-B-apoproteinemia may be an important risk factor for coronary heart disease. This evidence, and the possibility that apolipoprotein assays (in particular apoB and apoA-I assays) may serve as a better marker of risk for atherosclerosis than the standard lipid measurements, have been discussed by Brunzell et al. (B59). 

Response of total plasma cholesterol in patients with heterozygous familial hypercholesterolemia to diet (low cholesterol, low saturated fat) and hyperlipidemic drugs. 

The subjects in our study also developed hypocholesterolemia. The decline in total plasma cholesterol during manganese depletion in both studies is presumably related to the need for manganese at several sites in the synthesis of cholesterol (5). 

Soybean oil contains about 21% of the monounsaturate oleate. Studies have shown that the oxidation rate of oleate is much slower than that of the polyunsam-rates, linoleate and linolenate, which oxidize quickly and are the major contributors to the poor stability of soybean oil (287, 323). A diet high in monounsaturates may help to reduce elevated levels of total plasma cholesterol without reducing the high-density lipoprotein-cholesterol level (324). Therefore, high-oleate soybean oil is not only more stable than conventional soybean oil (275), but also has enhanced nutritive value. 

Consensus minimum targets for primary and secondary prevention of CHD with statins are a total plasma cholesterol of < 5 mmol/1 (or a reduction of 20-25% if the result is lower) or a LDL-cholesterol of < 3 mmol/1 (or a reduction of 30% if that is lower). These may be revised in the light of the Heart Protection Study (see... 

The hypolipidaemic effect of metformin has not been elucidated satisfactorily. The reduction of serum triglycerides and to a smaller extent total plasma cholesterol, however, is very welcome in the treatment of the metabolic syndrome in Type-II diabetes. The inhibitory effect of metformin on fatty acid oxidation (Schonborn et al., 1975) has been regarded as pivotal in its mechanism of antidiabetic action, because of the interrelations between fatty acid and carbohydrate metabolism. 

In the fasting state, most plasma triglycerides are present in VLDL. In the nonfasting state, chylomicrons appear transiently and contribute significantly to the total plasma triglyceride level. LDL carries about 70% of total plasma cholesterol but very little triglyceride (see Table 26-5). HDL contains about 20% to 30% of plasma cholesterol. 

LDL-receptor deficiency. In the normal condition (a), VLDL produced by the liver loses triacylglycerol as free fatty acids (FFA) via lipoprotein lipase to peripheral tissues and then proceeds down the metabolic cascade to IDL and LDL. A major portion of these two lipoprotein species is taken up by the liver or peripheral tissues via the LDL (apo B, E) receptor. In individuals with down-regulated or genetically defective LDL receptors (b), the residence time in the plasma of IDL is increa.sed, a greater proportion being converted to LDL. LDL production and turnover time are increased, and total plasma cholesterol levels become grossly abnormal. 

Bernnan EX. Job RS. Watkins LR. Maier SF. Total plasma cholesterol levels of rats are increased following only three sessions of tailshock. Life Sci 1992 50 945-950. 

When ACEIs are used to reduce proteinuria, it is common to see an accompanying decrease in total plasma cholesterol and the lipoprotein (a) level. Combined use of an ACEI with an HMG-CoA reductase inhibitor may therefore offer additional benefits in controlling nephrotic hyperlipidemia. 

---