Rosemarie Ostwald

Erythrocyte membranes-effect of increased cholesterol content on permeability

The permeability to several non-electrolytes and to Na+ of guinea pig erythrocytes containing different amounts of cholesterol was measured. A marked decrease of the permeability of the cholesterol-loaded erythrocytes to both hydrophilic and amphiphilic non-electrolytes and to both the active and the passive component of Na+ efflux was observed. We suggest that cholesterol loading causes a tighter packing of the lipid components which in turn decreases the mobility of the permeants within the membrane matrix.

Erythrocyte membranes - compression of lipid phases by increased cholesterol content

Abstract Lipid and protein interactions were studied in guinea pig erythrocytes containing a normal or a two-fold increased amount of cholesterol. The electron spin resonance (ESR) spectra of cholesterol-loaded cells labeled with fatty-acid probes showed an increase in the local viscosity of the membrane as compared with control cells. This increase reflects changes in the interior of the lipid matrix of the membrane because the probes resisted destruction by ascorbate, were unaffected by the action of pronase, and gave spectra similar to those of liposomes. No differences were observed between control and cholesterol-loaded cells in the conformation of the membrane proteins by either the infrared spectra or the ESR spectra of cells labeled with maleimide probes.

Histopathology of Guinea Pigs with Cholesterol-Induced Anemia.∗

Summary The response of guinea pigs to dietary cholesterol is unique among small animals. Instead of developing cardiovascular lesions, the guinea pig becomes acutely anemic. The anemia is accompanied by enlarged liver and spleen, and fatty infiltration of liver, spleen, lung, and kidney. Most of the organs showed striking pathological changes when examined microscopically. The liver showed lipid globules, erythropoiesis, spotty necrosis, accumulation of hemosiderin and cholesterol, and diffuse regeneration. Splenomegaly was due to erythropoietic proliferation, red cell congestion and, to a lesser degree, to fatty deposits. The primary change in the adrenal was a selective fatty infiltration of the zona fasciculata. The lungs showed fat globules in the histiocytes as well as fat emboli in the capillaries. The testes were small and poorly developed. Spermatogenesis was greatly impaired. The bone marrow was hyperplastic, and the kidney showed glo-merulosclerosis. The pancreas and heart were unaffected. The changes observed resulted primarily from alterations in the cellular structure caused by the accumulation of cholesterol, and secondarily from impaired liver function and the effects of the hemolytic process.

Effects of dietary cholesterol upon bile acid metabolism in guinea pig

Cholesterol fed guinea pigs develop a hemolytic anemia accompanied by high cholesterol concentrations in the liver, plasma, and red cells. We have studied the bile acid metabolism of guinea pigs fed a diet with or without cholesterol in a search for the factor(s) which prevent adequate control of their body cholesterol pool and, therefore, its pathological consequences. The results show that in the cholesterol fed guinea pig the synthesis (and excretion) of bile acids was at least three times greater than in controls. This is the result of a doubling of the fractional turnover rate and a smaller increase in the pool size. The major increase of the bile acid pool was in the liver. The main bile acid in gall bladder bile and small intestines was chenodeoxycholic acid, with smaller amounts of 7-ketolithocholic and ursodeoxycholic acids. In the caecum, large intestines, and feces, the major bile acid was lithocholic acid.

Plasma Cholesterol Esterifying Activity in Guinea Pigs

Plasma cholesterol esterifying activity has been measured in guinea pigs fed either a control diet or the same diet supplemented with 1% cholesterol. The extent of esterification was found to be similar in the cholesterol-fed and control guinea pigs and somewhat lower than in rats. The initial rate of esterification was also of the same magnitude as that found in rats and humans, and unaffected by dietary cholesterol if autologous plasma was used as substrate. However, LCAT activity from cholesterol-fed guinea pigs was significantly higher than that of control plasma when acting on either control or cholesterol-fed substrate. This suggests that dietary cholesterol increases the amount (or activity) of LCAT but that the substrate is unsuitable or that a necessary cofactor is present in limiting amounts. Heat treatment of guinea pig plasma seems to alter substrate availability to varying degrees. The implications of these findings in relation to substrate specificity and cofactor requirements of guinea pig LCAT are discussed.

Spiculated Erythrocytes of Cholesterol-Fed Guinea Pigs: Changes of Morphology, Composition, and Osmotic Fragility

Summary We have studied the sequential changes of cholesterol content and morphology in RBC of cholesterol-fed GP and the effects of these changes on their energy metabolism and osmotic fragility. The results suggest that (i) spurring of GP RBC is not accompanied by obvious alterations in their energy metabolism and may be the end result of sequential shape transformations associated with cholesterol-loading, and (ii) neither the morphological abnormalities nor the decreased osmotic fragility of cholesterol-loaded RBC is directly related to the development of the hemolytic anemia. Our thanks go to Dr. T. Hayes, Donner Laboratory, University of California, Berkeley, for the scanning electronmicrograph and for permission to publish it. The replicate experiment (Table I, Expt. 2) was carried out by Jacqueline Fields.

Lipoprotein lipase in cholesterol-fed and control guinea pigs.

A study of the in vitro activity of lipoprotein lipase of guinea pigs has shown that (a) the lipolytic activity of activated post-heparin serum is depressed in hypercholesteremic guinea pigs compared to the serum of normocholesteremic guinea pigs; and (b) this depressed lipolytic activity in hypercholesteremic guinea pigs is not due to the presence of an inhibitor.

Influence of sex and gonadal hormones on lipid metabolism in essential fatty acid-deficient rats

Previous work has shown differences between male and female rats in their ability a) to mobilize linoleic acid from adipose tissue when the supply is limited; b) to maintain higher levels of circulating and liver arachidonic acid when dietary linoleic acid is limited; c) to prevent accumulation of cholesteryl ester (CE) in the liver; and d) to increase the proportions of polyunsaturated fatty acids (PUFA) in their plasma lecithins.Recent studies are reviewed which show that a) essential fatty acid (EFA)-deficient rats exhibit the same kinds of sex differences as do rats on complete diets; b) these differences are mediated or at least influenced by estrogen; c) some of the differences may be attributed to differences in body size which result in less need for PUFA in structural phospholipid (PL); d) the rate of conversion of linoleic to arachidonic acid may differ under certain experimental conditions; and e) female rats have higher proportions of stearic and arachidonic acids in their liver lecithins than do males, which may relate to their higher rate of lecithin synthesis via methylation of phosphatidyl-ethanolamine.

Bone Marrow Composition of Cholesterol-Fed Guinea Pigs.

Summary The anemia produced in guinea pigs by dietary cholesterol led to a stimulation of erythropoietic activity with a proliferation of marrow cells which displaced the fat globules normally occupying the femoral marrow cavity. The triglyceride content decreased to half of its original level while the relative proportion of PL and cholesterol, on a dry, fat-free basis, remained unchanged. The proportion of linoleic acid in the remaining portion of TG decreased. Fractionation of the PL showed changes in their composition, particularly a decrease of the less polar components. The relationship of these changes in marrow to the changes observed in the peripheral blood requires further study.

Effect of dietary cholesterol on bile-acid composition of gall bladder bile from guinea pigs

The composition of gall bladder bile acids from control and cholesterol-fed, anemic guinea pigs was analyzed by thinlayer-chromatographic and colorimetric techniques. In both control and cholesterol-fed animals, the gall bladder bile acids constituted about one third of the total bile solids. The main component of the bile acids of both groups of animals was chenodexycholic acid, which was predominantly conjugated with glycine. No cholic acid was present although this is the main bile acid in most mammals. The major difference in bile composition between control and cholesterol-fed animals was the conjugation pattern of chenodeoxycholic acid. The ratio of glycochenodeoxycholic to taurochenode-oxycholic acid was high, 6.4, for control animals, and decreased to 2.4 for the cholesterol-fed, anemic animals. Impaired liver function, limited availability of glycine, and greater efficiency of taurocholanic acids for the disposal of excess cholesterol may be involved in the mechanism for this phenomenon.