A sensitive and specific double antibody radioimmunoassay for the major apolipoprotein (apo B) of human serum very low density lipoprotein (VLDL) and low density lipoprotein (LDL) is described. Using anti-LDL and anti-apo B antibodies the immunoreactivity of LDL and apo B were compared. Human LDL and its isolated apo B were not immunologically identical when each antiserum was used with its homologous label; a population of antibodies was selected which reacted with antigenic sites unique to the antigen itself as well as to those which were common to the closely related protein. When the heterologous label was used with either antiserum, a population of antibodies directed against antigenic sites shared by the LDL and apo B molecules was selected.Apo B in sera samples can be measured using either anti-LDL or anti-apo B antibodies provided that intact LDL was used for preparation of the iodinated tracer and standard. Serum apo B levels in healthy normolipidaemic males and females were 0.93 f 0.25 g/l (range 0.58-1.39) and 0.90 f 0.15 g/l (range 0.58-1.12), respectively. The total cholesterol and apo B, and phospholipid and apo B concentrations for both males and females were significantly correlated (P < 0.05). In another normolipidaemic population (n = 52), total serum apo B values correlated positively with LDL cholesterol (r = 0.92, P < 0.001).Apo B was measured in sera from patients with abetalipoproteinaemia, familial hypercholesterolaemia and Tangiers disease. Apo B was not detected in the serum of subjects with abetalipoproteinaemia, while the apo B level in the familial hypercholesterolaemic subjects was significantly elevated (range 3.26-4.94 g/l) compared to normals (P

Proinsulin-like components (PLC) and insulin have been measured in 24 hr urine samples from 8 healthy subjects. The mean excretion of PLC was 45.8 ng and that of insulin 314 ng; the PLC: insulin ratio was 0.14. Urinary PLC was increased 3.5 fold in a patient with a pancreatic islet cell tumor and the PLC: insulin ratio was 0.35. The urinary PLC: insulin ratio is lower than that of serum, presumably because of the relatively lower urinary clearance of the larger molecular weight PLC.

Over the course of a 2-year study, two male rhesus monkeys underwent episodes of diet-induced hypercholesterolemia (from a diet supplemented with 25% coconut oil and 2% cholesterol) followed by regression phases in which the animals received a low fat Purina chow diet. During the induction of hypercholesterolemia, serum cholesterol, apo B, saturation of low density lipoprotein (LDL) cholesteryl ester fatty acyl chains, and the ability of the serum to stimulate cholesterol esterification by smooth muscle cells rose immediately and in parallel, whereas there was a lag period before the serum became mitogenic to smooth muscle cells. A dministration of diets rich in saturated fats and cholesterol to rhesus monkeys results in increased levels of serum cholesterol which are mainly due to higher concentrations of low density lipoproteins (LDL). These lipoproteins have altered physical and chemical properties as manifested by their increased molecular weight and a relatively high content of free cholesterol and cholesteryl esters but a low content of triglycerides.1 -5 These LDLs also ex-

Two male rhesus monkeys underwent cyclical feeding of a hypercholesterolemlc diet (2% cholesterol, 25% coconut oil) and a low-fat Purina monkey chow diet. During the latter diet, high density lipoprotein (HDL) exhibited two components with peak densities of d = 1.081 g/ml and 1.109 g/ml named HDL L and HDLH, respectively. During the Initial hypercholesterolemic stage, except for apo A-ll which remained unchanged, there was a transient rise In HDL (mainly HDLJ as well as in HDL cholesterol and apo A-l, all reaching maximal values after about 2 weeks from the onset of the diet. The two HDL species changed neither In size nor density as compared to their baseline counterparts, but had a comparatively higher content In cholesteryl ester and lesser amounts of triglycerides and phospholipids as compared to the normocholesterolemic animal. With the development of overt hypercholesterolemia (plasma cholesterol levels above 400 mg/dl), both HDL particles increased in density due to the loss of surface components (phospholipids and unesterlfled cholesterol) and core triglycerides with only minor changes in protein and cholesteryl ester contents. At this stage, the same two animals exhibited significant changes in the size and buoyant density of LDL. When returned to a normal Purina chow diet, the animals' serum cholesterol levels declined rapidly to normal levels; normalization of the HDL distribution also occurred but at a comparatively later time (26 weeks).Our studies Indicate that the two HDL subsets characteristic of the normocholesterolemic rhesus monkey undergo significant changes in buoyant density as a function of the stage of hypercholesterolemia and that changes In concentration and size mainly affect the HDL L subspecies. At levels of plasma cholesterol below 400 mg/dl, this cholesterol Increment Is reflected by a significant increase in the number of the HDL subspecies without the overt participation of the low density lipoprotein classes characteristic of the advanced hyperlipldemlc stage. Since we previously reported that greatly increased levels of cholesteryl esters enriched low density lipoproteins, (J-VLDL (very low density lipoprotein) and pre-B-VLDL during overt diet-Induced hypercholesterolemia, it is apparent that cholesterol is distributed differently among lipoprotein particles containing either apo A-l, apo B, or apo E depending on its concentration In plasma. (Arteriosclerosis 4:154-164, March/April 1984) R hesus monkeys fed high cholesterol diets develop altered concentrations of plasma lipoproteins. Since there may be a causal relationship between the level of serum low density lipoprotein (LDL) and atherosclerosis, most attention has been focused on LDL. However, the concentration and Received July 7,1983; revision accepted November 18, 1983. density distribution of HDL species are also affected by cholesterol-containing diets. Thus, it was observed that high density lipoprotein (HDL) levels were temporarily increased in rhesus and sooty mangabey monkeys on a high cholesterol diet but fell...

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