Elwood E. Largis

Hypercholesterolemia in the Rabbit Induced by Feeding Graded Amounts of Low-Level Cholesterol: Methodological Considerations Regarding Individual Variability in Response to Dietary Cholesterol and Development of Lesion Type

While a number of studies have presented detailed examinations of lesion development in the cholesterol-fed rabbit, individual variability in response to cholesterol feeding and type of lesion produced relative to the degree of cholesterol exposure is not well defined. This study analyzed such critical parameters in an attempt to further characterize the model and establish a baseline for future testing of treatments targeted at limiting atherosclerosis. For these experiments, male New Zealand White rabbits were fed atherogenic diets consisting of 0.05%, 0.10%, 0.15%, 0.20%, or 0.25% cholesterol dissolved in 6% peanut oil for 31 to 32 weeks. Raising dietary cholesterol from 0.05% to 0.15% resulted in a less than twofold stepwise increase in total plasma cholesterol (TPC) exposure (area under plasma cholesterol versus time curve), whereas further increases in cholesterol intake resulted in an exponential four- to fivefold increase in TPC exposure. Regression analysis of TPC exposure with aortic sudanophilia demonstrated a threshold of approximately 5000 cholesterol weeks; below this limit lesions were minimal, and above this value the degree of plaque correlated with TPC exposure. Furthermore, a wide biological variability occurred among rabbits with respect to individual responsiveness to dietary cholesterol. In the aorta, various types of plaques, from fatty streaks to atheromatous lesions, were observed, depending on the degree of cholesterol intake. Diets consisting of < 0.15% cholesterol resulted in the development of fatty streak lesions, while transitional lesions and atheromatous plaques were mostly found with higher cholesterol feeding. Coronary artery atherosclerosis was present in > 50% of animals fed diets > or = 0.15% cholesterol. Despite the level of TPC exposure, coronary lesions in epicardial vessels were generally the fibrous type, whereas intramyocardial arteries demonstrated predominantly intimal foam cells. In conclusion, by adjusting dietary cholesterol intake and selecting rabbits with a similar responsiveness to cholesterol, the overall cholesterol exposure can be more closely controlled to minimize the inherent individual variability among animals in this model. The nature of the target lesion must also be carefully considered, because the efficacy of some treatments may depend on the type of atherosclerotic plaque.

2,4-thiazolidinediones as potent and selective human β3 agonists

Methylsulfonamide substituted 2,4-thiazolidinedione 22c is a potent (EC50=0.01 microM, IA=1.19) and selective (more than 110-fold over beta1 and beta2 agonist activity) beta3 agonist. This compound has also been proven to be active and selective in an in vivo mode.

4-Aminopiperidine ureas as potent selective agonists of the human β3-Adrenergic receptor

The preparation and structure-activity relationships (SARs) of potent agonists of the human beta(3)-adrenergic receptor (AR) derived from a 4-aminopiperidine scaffold are described. Examples combine human beta(3)-AR potency with selectivity over human beta(1)-AR and/or human beta(2)-AR agonism. Compound 29s was identified as a potent (EC(50)=1nM) and selective (greater than 400-fold over beta(1)- with no beta(2)-AR agonism) full beta(3)-AR agonist with in vivo activity in a transgenic mouse model of thermogenesis.

Antilipolytic Action of Tolbutamide in Isolated Fat Cells of the Rat

Concentrations of tolbutamide from 0.25 to 4.0 mg. per milliliter were found to inhibit epinephrine-stimulated lipolysis in isolated fat cells of the rat. At a concentration of 1 mg. per milliliter, tolbutamide also inhibited lipolysis stimulated by ACTH or dibutyryl cyclic AMP. At the same concentration it failed to alter basal lipolysis, basal or epinephrine-stimulated cyclic AMP levels. Basal and epinephrine-stimulated adenylate cyclase and glycogen phosphorylase as well as binding of cyclic AMP to protein kinase were unaltered. These data are discussed in relation to the antilipolytic mechanism of tolbutamide.

Novel substituted 4-aminomethylpiperidines as potent and selective human β3-agonists. Part 2: Arylethanolaminomethylpiperidines

The synthesis and SAR of a series of beta3 adrenoreceptor agonists based on a novel template derived from 4-aminomethylpiperidine coupled with a common pharmacophore, arylethylamine, is described. This combination led to the identification of human beta3 adrenoreceptor agonists with in vivo activity in a transgenic mouse model.

Effects of phlorizin on glucose transport into blood and lymph

Abstract Phlorizin was administered by oral and intraperitoneal routes to rats prepared with cannulated mesenteric lymph ducts. Oral phlorizin (fed with glucose by stomach-tube) depressed the uptake of fed glucose into both blood and lymph. No inhibition of water transport occurred while glucose transport was decreased, yet very high levels of oral phlorizim (220 μmoles) would block water transport to lymph from the intestine. Intraperitoneally injected phlorizin did not show an effect on glucose transported by lymph or blood, but did promote glycosuria. Typical findings are presented in the text.

Transport of amino acids via the mesenteric lymph duct in rats.

Summary It was demonstrated that dietary amino acids appear in the mesenteric lymph and are transported from the intestinal lumen both as free amino acids and newly synthesized protein via the lymphatic system. The amino acid profiles in intestinal lymph are compared to those in plasma and the intestinal mucosa. There seems to be a depression of lymph amino acid levels during the early phase of intestinal absorption which returns to normal in the later phase. This depression occurs at the same time the newly synthesized protein appears in the lymph.

Effect of Varying K+ Concentrations on Phosphorylase Activity, Lipolysis, and cAMP Levels in Perfused Rat Heart

Summary Rat hearts were perfused with 5.6, 16, or 55 mM K+ buffer for 10 min. IPR (3 × 10−8 M) was infused and hearts assayed for cAMP and phosphorylase activation while the perfusate was assayed for glycerol and αGP. Both 16 and 55 mM K+ buffer blocked contraction of the heart. With infusion of IPR spontaneous contractions occurred, a delayed elevation of cAMP was observed, and also a delayed release of glycerol and αGP into the perfusate was detected when compared to 5.6 mM K+ perfused hearts. Hearts perfused with 55 mM K+ buffer revealed no increase in cAMP and no increase in the perfusate of glycerol and αGP after IPR infusion. Phosphorylase was elevated in 5.6, 16 and 55 mM K+ perfused hearts.

Effect of protein inhibitors on protein and amino acids in mesenteric lymph.

Summary The effects of the protein antagonists cycloheximide and puromycin upon the transport of amino acids and newly synthesized protein into the mesenteric lymph of the intact rat was investigated. Upon feeding a fatty meal (bovine cream) fortified with leucine-14C these antagonists depressed the formation of lymph protein with a concurrent increase of amino acids, as measured chemically and by tracing radioactivity of these fractions. The influence of cycloheximide was more lasting than puromycin. These two antagonists affect protein synthesis differently as evidenced by the rates of new protein synthesis and the nature of the amino acids transported by the lymph leaving the upper small intestine.