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Biomedical subjects

T B Clarkson

Publications and source records attributed to T B Clarkson.

At least 109 records · Page 6Linked to original sources
PubMed1983

Influence of a levonorgestrel-containing contraceptive vaginal ring on plasma lipids and lipoproteins in cynomolgus monkeys.

The effect of a contraceptive vaginal ring (CVR) containing levonorgestrel on plasma lipid and lipoprotein concentrations and characteristics was assessed in ten cynomolgus monkeys. The animals were fed a diet similar to the average American diet in fat (40% of calories) and cholesterol (0.2 mg/kcal) content. The objective of this study was to determine if changes in lipids and lipoproteins caused by progestogen administration parallel those seen in human females. A parallel pattern would recommend the cynomolgus monkey as a model for studying the effects of progestogens on the atherosclerotic process. Treatment with the CVR resulted in significant decreases in total plasma, VLDL + ILDL + LDL, and HDL cholesterol concentrations and a decrease in the percentage of HDL2 in total HDL. Plasma triglyceride concentrations were low throughout the study and consistent effects of the CVR were not seen. CVR treatment resulted in increases in TPC:HDL-C ratios and in the flotation rate of the LDL particle. The patterns of effects on HDL cholesterol, total plasma cholesterol, and HDL2 concentrations were similar to the progestogen-induced changes observed in human plasma lipids and lipoproteins. Based on these effects, the cynomolgus monkey appears to be a suitable model for the study of progestogen-induced changes in plasma lipids and lipoproteins and their consequent influences on coronary artery atherosclerosis.

Animals↗
PubMed1983

Effects of gender and social behavior on the development of coronary artery atherosclerosis in cynomolgus macaques.

This experiment involved examination of the effects of gender and social status ('competitive dominance') on the coronary artery atherosclerosis of cynomolgus monkeys. Thirty-two adult Macaca fascicularis (16 males, 16 females) were fed a diet containing a moderate amount of cholesterol (0.56 mg/cal) for 16 months. The monkeys were housed in groups of 4 animals of the same sex, and all groups were stable in composition for the entire experiment. After 1 year a'competitive dominance' score was determined for each monkey, based on feeding order in 9 trials involving a preferred food as incentive. At necropsy the coronary arteries were pressure perfused; 5 sections each were then taken from the left anterior descending, left circumflex and right coronary arteries. For each animal, the mean percent lumen stenosis calculated from theses 15 sections was used as the index of extent of coronary artery atherosclerosis. Males had significantly more extensive coronary artery atherosclerosis than did females. Further, among both males and females, submissive animals (low in competitiveness) had more extensive coronary artery stenosis than did their dominant (highly competitive) counterparts. A similar pattern was observed in the thoracic and abdominal portions of the aorta with respect to competitiveness, but not gender. In the iliac artery, females had less atherosclerosis than males but there was no competitiveness effect. The gender and social status effects on atherosclerosis were each statistically independent of variability in clinical-pathological measures (serum lipid concentrations and heart weight). The results indicated that: (a) gender and psychosocial stress independently affect the development of coronary artery atherosclerosis; (b) the mechanisms mediating these effects remain unknown; and (c) the cynomolgus macaque is a good model for the study of such phenomena.

Animals↗
PubMed1983

Social instability and coronary artery atherosclerosis in cynomolgus monkeys.

Epidemiologic research has increasingly implicated psychological factors in the emergence of atherosclerotic coronary heart disease in human beings. The study of behavioral influences on atherogenesis in man, however, is impeded by the difficulty of assessing coronary artery atherosclerosis in asymptomatic individuals and by the fact that significant arterial lesions typically develop only over relatively protracted intervals. Consequently, we have recently attempted development of an appropriate animal model for examining the atherogenic effects of psychosocial variables. In the first of two investigations, an experimental stressor--involving repeated reorganization of socially housed groups of adult, male cynomolgus monkeys (Macaca fascicularis) fed a moderately atherogenic diet--resulted in increased coronary artery atherosclerosis relative to control animals, though only among monkeys which retained dominant social status over the 22 months of the study. In the second investigation, which employed the same experimental procedures among monkeys fed a low cholesterol/low saturated fat diet, periodic social group reorganization similarly led to development of greater atherosclerosis in the coronary arteries. In neither experiment were psychosocial influences on coronary atherogenesis attributable to the concomitant effects of other physiologic variables commonly associated with atherosclerosis (e.g., serum lipids, blood pressure).

Aggression↗
PubMed1983

Behaviorally induced heart rate reactivity and atherosclerosis in cynomolgus monkeys.

It has been suggested that individual differences in behaviorally induced cardiovascular reactivity may mediate associations between behavioral factors and atherosclerotic disease. The present study provides data relevant to this hypothesis within an animal model. Experimental animals were 26 adult, male cynomolgus monkeys that had been fed a moderately atherogenic diet for 22 months. In the weeks preceding termination of these animals, monkeys were fitted with electrocardiogram (EKG) telemetry devices and their heart rates (HRs) recorded under baseline and stressed conditions. Stress-period HR measures were obtained during a standard challenge involving threatened capture and physical handling of the animals. At necropsy, the coronary arteries were subjected to pressure fixation and sections taken from the left main, left anterior descending, left circumflex, and right coronary arteries. Mean intimal area measurements, calculated for each artery, were then compared between animals identified as High (n = 8) and Low (n = 8) HR reactors during stress. Results indicated that High HR reactors had significantly greater coronary artery atherosclerosis than did Low HR reactive animals, both in individual arteries and on an overall coronary index. Atherosclerosis in the thoracic aorta was found to differ similarly between High and Low HR reactors. Additional analyses revealed that High HR reactors were significantly more aggressive, more ponderous, and had greater heart weights than did Low HR reactors. Although groups did not differ in resting HRs, body weights, or lipid values, high-density lipoprotein (HDL) cholesterol comprised a slightly smaller fraction of the total serum cholesterol of High, relative to Low, HR reactive monkeys. It is concluded that these findings provide initial support for the hypothesis that cardiovascular hyperresponsiveness under stress is related to the development of atherosclerosis.

Aggression↗
PubMed1983

Increased atherosclerosis and glomerulonephritis in cynomolgus monkeys (Macaca fascicularis) given injections of BSA over an extended period of time.

A study was conducted to compare the effects of experimental immune complex disease on the development of glomerulonephritis and aortic and coronary artery atherosclerosis. Fourteen adult male macaques (Macaca fascicularis) were fed a mildly atherogenic diet. Ten of these animals were given repeated intravenous injections of bovine serum albumin (BSA), and the remaining 4 were given similar injections of saline. Three of the monkeys given BSA responded with a high antibody titer, 4 with a moderate titer, and 3 with a low level titer to BSA. In all 4 monkeys with the moderate antibody response glomerulonephritis developed, characterized by increased glomerular cellularity, electron-dense deposits in the glomerular capillary basal lamina, and deposits of IgG, IgM, C3, C4, and BSA. Glomerulonephritis was not seen in the other 6 monkeys given BSA or the 4 control monkeys. Aortic lesions seen at necropsy consisted of a few fatty intimal streaks with no differences between test monkeys (given BSA) and control monkeys (given saline). There was no correlation between total serum cholesterol concentration, high-density lipoprotein cholesterol concentration, or BSA antibody levels and the degree of aortic atherosclerosis. Immunochemical stains for immunoglobulins and complement components revealed increased intimal staining when intimal thickness increased. Medial staining for immunoglobulin and complement components appeared to be slightly increased in monkeys with moderately high-level titers of BSA. The extent of atherosclerosis in the coronary arteries of monkeys given BSA was greater than in the control animals. Differences in the extent and severity of the atherosclerotic lesions were most pronounced in the proximal portions of the main coronary arteries, suggesting an increased susceptibility of this site to immune-complex-exacerbated atherosclerosis. In addition to the increased lesion severity in monkeys given BSA, there were numerous granulocytes seen within, attached to, and penetrating into the intima of the coronary lesions. No correlation was seen between the development of glomerulonephritis and either aortic or coronary artery atherosclerosis.

Animals↗
PubMed1982

Hypolipidemic effects of gossypol in cynomolgus monkeys (Macaca fascicularis).

The effect of gossypol acetic acid (gossypol) on plasma lipid concentrations was studied in adult male cynomolgus monkeys consuming a diet containing 0.19 mg cholesterol/Kcal. Gossypol was administered orally at 5 (n = 4) or 10 (n = 3) mg/kg/day for 6 months. A significant decrease in total plasma cholesterol (TPC) and low density lipoprotein and very low density lipoprotein-cholesterol (LDL + VLDL-chol) concentrations was observed without any significant decrease in plasma high density lipoprotein-cholesterol (HDL-chol) levels among 10 mg/kg/day gossypol-treated animals. This is a new therapeutic property of gossypol that has been previously reported. No appreciable differences were observed in plasma levels of TPC and LDL + VLDL-chol among 5 mg/kg/day gossypol-treated animals when compared to controls until the gossypol dosage was increased to 10 mg/kg/day, thus suggesting that hypolipidemic effect of gossypol is dose-dependent. In general, no adverse clinicopathological findings were noted except a temporary diarrhea and loss of appetite among 10 mg/kg/day gossypol-treated animals during the initial stages of treatment. In conclusion, it is tempting to speculate that gossypol might possibly reduce the intestinal absorption of dietary cholesterol or it may reduce the hepatic synthesis of low density lipoproteins. These results also suggest that gossypol may be a particularly useful drug in lowering plasma cholesterol concentrations in addition to its previously demonstrated antifertility properties in males.

Animals↗
PubMed1982

Cardiovascular complications.

This report summarizes the current state of knowledge concerning the cardiovascular system in various animal models of diabetes and presents their major strengths and weaknesses for studying the important research questions in the field. Nonhuman primates have many desirable features for studies on the macrovascular and cardiac complications of the disease as well as risk factor alterations, but their availability, cost, and maintenance present practical disadvantages. The spontaneous rodent models of diabetes currently are not considered very useful for cardiovascular research, but they have not been well characterized with respect to most aspects of their cardiovascular system. Alloxan-diabetic rabbits offer some promise for examining the effects of diabetes on atherogenesis, lipoprotein metabolism, and cardiomyopathy, but additional research is required to validate their usefulness. Insufficient data are available on canine and swine models of diabetes to judge their merits for cardiovascular research. The Task Force recommends: (1) additional longterm investigations to determine the extent and severity of cardiovascular complications in the well-characterized rodent models and in diabetic rodents with multiple risk factor abnormalities; (2) further studies on the macrovascular disease and lipoprotein abnormalities of the alloxan-diabetic rabbit and the development of rabbit colonies with spontaneous diabetes; (3) increased emphasis on such potentially important but neglected areas of research in diabetic animals as the intramyocardial circulation, adventitial blood vessels, blood pressure, platelet function, blood coagulation, blood rheology, and autonomic nervous function; (4) long-term studies on the influence of control of hyperglycemia and of insulin therapy on cardiovascular complications in diabetic animals; and (5) encouragement of use of diabetic nonhuman primates for cardiovascular research and institution of measures to increase their supply and availability by expanding current colonies, screening newly imported animals for diabetes, and establishing a visiting scientist's program allowing investigators to study diabetic primates at resource centers.

Animals↗
PubMed1980

Long-term vasectomy: effects on the occurrence and extent of atherosclerosis in rhesus monkeys.

We demonstrated previously that atherosclerosis develops more extensively in vasectomized cynomolgus macaques fed an atherogenic diet and speculated that the immunologic response to sperm antigens may have exacerbated the atherosclerosis. We report here that rhesus monkeys vasectomized for 9-14 yr and fed monkey chow (devoid of cholesterol and low in fat) rather than an atherogenic diet also had more extensive and severe atherosclerosis than did control animals of the same age. The extent of atherosclerosis was considered as the percentage of intimal surface with plaques. No control animals were found to have plaques in the thoracic aorta, but 7 of 10 vasectomized monkeys were affected. The plaques in the vasectomized monkeys occupied about 13% of the intimal surface. In 4 of 7 control monkeys and 7 of 10 vasectomized monkeys there were lesions in the abdominal aortas; the lesions were considerably more extensive and severe in the vasectomized animals. Lesions were also more common in iliac arteries of vasectomized animals, and the extent was increased about threefold. Plaques were seen at the carotid bifurcation in all of the animals of both the control and vasectomized groups. The carotid bifurcation plaques of the vasectomized monkeys were larger than those of the control animals on the right but not on the left side. Histologically, the lesions of vasectomized monkeys did not appear to be qualitatively different from those of control animals, even though they were larger and contained more collagen, lipid, and mucopolysaccharides. Grossly, the distribution of the lesions in the vasectomized animals was different from that in the control animals, and that of lesions induced by atherogenic diets, i.e., the lesions were distributed randomly within the artery rather than around bifurcations. More extensive atherosclerosis was noted among vasectomized animals that were found to lack demonstrable circulating free antisperm antibodies. On the basis of the observations made in this study, we suggest that the antisperm antibodies that form after vasectomy may result in circulating immune complexes that exacerbate atherosclerosis.

Animals↗
PubMed1980

A study of atherosclerosis regression in Macaca mulatta: III. Chemical changes in arteries from animals with atherosclerosis induced for 19 months and regressed for 48 months at plasma cholesterol concentrations of 300 or 200 mg/dl.

The influence of two levels of plasma cholesterol concentration on the long-term regression of atherosclerotic plaques in rhesus monkeys (Macaca mulatta) was studied. Forty-eight young adult male rhesus monkeys were fed an atherogenic diet for 19 months, then diets designed to maintain plasma cholesterol concentrations at 280-320 mg/dl (actual 316 +/- 10 mg/dl; mean +/- SEM) of 180-220 mg/dl (actual 204 +/- 4 mg/dl). Twelve animals were killed after 19 months to evaluate the atherosclerosis produced. The remaining 36 monkeys were studied after 48 months of atherosclerosis regression. Significantly greater amounts of accumulated nonesterififed and esterified cholesterol were lost from the arteries of monkeys that underwent regression at about 200 mg/dl, in comparison with 300 mg/dl. Regression at both plasma cholesterol concentrations resulted in increased collagen and decreased elastin content in the thoracic aorta but not in the other arteries studied. After regression at 300 mg/dl there was no change (83%) in the frequency of calcification of the thoracic aorta, while at 200 mg/dl the frequency of calcification was reduced to 50%. When compared with monkeys whose athersclerotic lesions were produced in an identical manner but were regressed for only 24 months, after 48 months had increased cholesterol concenrations in the thoracic aorta and carotid artery but not the abdominal aorta of iliaco-femoral artery, regardless of the plasma cholesterol concentration. The lipid composition of the regressed plaque suggested a change in plaque lipid toward the character of extracellular deposits described physically as crystalline in nature. The physical state was influenced by the length of the regression period and the plasma cholesterol concentration during regeression. In the thoracic aorta, principally as a result of changes in elastin content, the collagen-to-elastin ratio increased between 24 and 48 months of regression. It is proposed that the differences in removal of cholesterol from the thoracic and abdominal aorta after 24 and 48 months of regression in animals at 300 mg/dl may be influenced by the rearrangement of connective tissue. On the basis of the lipid and mineral content of uncomplicated atherosclerotic plaques after 4 yers of regression, it appears that the plasma cholesterol concentration during the regression period is a signigicant factor influencing the extent of plaque regression as well as the potential for further progression.

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