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Biomedical subjects

G L Todd

Publications and source records attributed to G L Todd.

29 records · Page 2Linked to original sources
PubMed1979

Temporal changes in endocardial energy metabolism following propranolol and the metabolic basis for protection against isoprenaline cardiotoxicity.

Propranolol infusions in open-chested, anesthetised dogs increased endocardial levels of ATP and phosphocreatine. It reduced ADP, AMP, glucose-6-phosphate and lactate in this region. Endocardial glycogen was transiently increased. Metabolic perturbations in the endocardium produced by cardiotoxic doses of isoprenaline were prevented or reduced by propranolol pretreatment. Thus, propranolol appears to have a more selective action on endocardial versus midmyocardial or epicardial metabolism.

Adenosine Diphosphate↗
PubMed1979

Transmural distribution of metabolites and blood flow in the canine left ventricle following isoproterenol infusions.

The effects of intravenous infusions of isoproterenol (0.1, 1.0 or 2.5 micrograms/kg/min for 1 hr) on the transmural distribution of myocardial high-energy phosphates and glycolytic intermediates were determined in anesthetized, open chested dogs. The transmural distribution of blood flow across the left ventricular wall was determined after serial injections of 15 mu radioactively labeled microspheres. A biopsy of the posterolateral wall was frozen in liquid nitrogen, divided into epicardial, midmyocardial and endocardial thirds, and assayed for metabolites. The remainder of the heart was processed for light and electron microscopy. At the infusion rate of 2.5 micrograms/kg/min, isoproterenol caused nonuniform reductions in ATP, phosphocreatine, total adenine nucleotides and glycogen, which were particularly depleted in the endocardium. Isoproterenol also caused nonuniform increases above baseline in blood flow (epicardial, 492%; midmyocardial, 197%; and endocardial, 131%). The endocardial/epicardial blood flow ratios, however, were reduced. Evidence of cellular damage was demonstrated by the presence of numerous contraction band lesions along with mitochondrial swelling and the appearance of electron-dense deposits. It is concluded that necrogenic infusions of isoproterenol impair myocardial energy production in all myocardial layers despite an overall increase in blood flow. There appears to be a link between the gradients in metabolites and the distribution of blood flow such that the endocardium becomes more vulnerable to injury.

Animals↗
PubMed1977

Influence of environmental stress on pathogenesis of sudden cardiac death.

The effects of 20th-century stress on the cardiovascular system are reviewed and correlated with experimental animal models. A classic example of such stress is drawn from a study of the aerospace workers at Cape Kennedy who were shown to be exposed to excessive occupational stress. Surprisingly, the usual risk factors did not predict a greater risk, yet the population exhibited a higher incidence of sudden cardiac death and acute myocardial infarction. Acute myocardial necrosis was much more frequently demonstrated than was acute coronary obstruction of any type. Retrospective coroner's studies revealed two types of myocardial necrosis: 1) elongated, thinned or wavy fibers and 2) anomalous contraction bands. Correlation of these clinical observations with experimental data was duplicated in canine models of myocardial infarcion and/or catecholamine-induced necrosis. Catecholamines can lead to irreversible myocardial necrosis but the underlying mechanisms appear to be complex. Extrapolation of the results from the experimental and clinical studies suggests that environmental stress can lead to myocardial necrosis.

Adenosine Triphosphate↗
PubMedDate not supplied

Effects of chronic non-ketotic diabetes and aging on myocardial function and fatty acid oxidation.

The effects of aging and chronic non-ketotic diabetes on contractile properties, oxygen consumption, palmitate oxidation and morphology were studied in isolated, perfused working hearts of 2, 9, 12 and 22 month old rats. The heart rate, coronary flow, and oxygen consumption were no different among the 9, 12 and 22 month control and diabetic hearts. Cardiac work was not depressed in control hearts until 22 months of age. Depression of cardiac output due to aging in the control hearts progressed in stages. The superimposition of chronic diabetes in the 9, 12 and 22 month rats did not further depress the cardiac work or cardiac output. [1-14C] palmitate oxidation in the 2 and 9 month control hearts was higher than that of the 12 and 22 month controls. Chronic diabetes did not affect fatty acid oxidation in the 9 and 12 month rats compared to their controls, but was diminished in the 22 month diabetic rat heart. These results suggest that impairments in the contractile properties of the isolated hearts of the chronically diabetic, senescent rats were primarily due to aging.

Aging↗
PubMedDate not supplied

Application of the MRFIT smoking cessation program to a healthy, mixed-sex sample.

The Multiple Risk Factor Intervention Trial (MRFIT) included a smoking cessation program that was highly successful (40.3% abstinence prevalence rate at 48-month follow-up) when used with other interventions for a male, middle-aged population at high risk for coronary heart disease (CHD). Our study employed the MRFIT cessation program alone with a mixed-sex, mixed-age, healthy population. We wished to determine its effectiveness when applied in a manner similar to other smoking cessation programs. Fifty-six subjects participated in a 10-week intervention followed by maintenance or extended intervention programs. The 52% abstinence prevalence rate at the end of the 10-week intervention dropped to 32% after four months, 25% at eight months, 25% at 12 months, and 27% at 16 months. The higher cessation rates of the original MRFIT study may be related to motivation and other characteristics of the high-risk population and to the combination of the smoking component with other interventions for CHD, rather than to the characteristics of the smoking intervention itself. Although the MRFIT program is comprehensive and includes vigorous maintenance activities, it is also expensive and may not be cost-effective or as desirable as programs with slightly lower cessation rates.

Adult↗