Biomedical subjects
J L Knittle
Publications and source records attributed to J L Knittle.
Conference on the American diet: healthy or hazardous?
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The role of adipose cell size and adipose tissue insulin sensitivity in the carbohydrate intolerance of human obesity.
Glucose metabolism and insulin sensitivity of isolated human adipose tissue was studied as a function of adipose cell size and number. Glucose metabolism by these tissues was closely related to the number of cells in the fragment, irrespective of cell size. Adipose cells of obese individuals metabolized glucose to carbon dioxide and triglyceride at rates similar to adipose cells of nonobese subjects. In contrast, insulin responsiveness of adipose tissue was dependent upon adipose cell size. The larger its adipose cells the less insulin sensitive was the tissue. Thus, adipose tissue of obese subjects, with enlarged cells, showed a diminished response to insulin. After weight loss and reduction in adipose cell size, insulin sensitivity of the adipose tissue of obese patients was restored to normal. When adipose tissue of obese individuals showed impaired responsiveness to insulin, their plasma insulin levels, after oral glucose, were elevated. Weight loss and reduction in adipose cell size restored plasma insulin concentration to normal, concomitant with the return of normal tissue insulin sensitivity.
Effect of early nutrition on the development of rat epididymal fat pads: cellularity and metabolism.
The effect of infantile nutritional levels on adipose tissue cellularity and metabolism was studied in two groups of Sprague-Dawley rats. Caloric intake was varied during the suckling period by manipulating litter size immediately after birth; however, all animals had free access to food after weaning. The epididymal fat pads of animals raised in small litters were heavier than those of their paired siblings raised in large litters. Initially, the differences in pad weight were accounted for primarily by differences in total cell number; however, at 20 wk both cell number and cell size contributed equally. The rate of glucose incorporation into CO(2) and triglyceride during in vitro incubations was the same for both groups if expressed on a per cell basis; therefore total tissue incorporation was greater in animals with more cells. The results support the hypothesis that early nutritional experiences can effect permanent changes in the cell number and size of the epididymal fat depot and that total cell number is important in the total metabolism of this organ. These findings and the fact that extreme human obesity is accompanied by similar alterations in cellularity and metabolism indicate that early nutritional experiences should be studied further as a guide to the etiology of obesity in man.
Effect of chain length on rates of uptake of free fatty acids during in vitro incubations of rat adipose tissue.
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The response of obese patients to weight reduction. II. A quantitative evaluation of behavior.
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Blood pressure, body composition, and fat tissue cellularity in adults.
While total body mass has been recognized for many years as having a strong positive association with blood pressure, it is not known whether body mass per se is important in this association or if a component of total mass, such as lean body mass or total body fat, is responsible for the relationship. To determine the relative importance of these components, 217 healthy adults unselected with respect to blood pressure or body composition, who were 18 to 49 years of age (X +/- sd = 33.1 +/- 8.9 years) had body density measured by underwater weighing. Body density was used to estimate percent body fat from which lean body mass and total body fat mass were determined. In addition, an adipose tissue biopsy from the gluteal area was made, and average fat cell size was measured using the osmium tetroxide method; fat cell number was then estimated. In both males and females, after adjusting for age, there were highly significant, positive partial correlations (r = 0.2 to 0.3) between measures of blood pressure (systolic, diastolic, and mean arterial) and percent body fat, total body fat mass or fat cell number. No significant correlation existed between lean body mass or fat cell size and any measure of blood pressure. These findings suggest that fat mass as opposed to body mass, per se, may be an important etiological component in elevated blood pressure in adults.
Effect of emulsions of medium and long chain triglyceride on human adipose tissue prostaglandin production in vitro.
Preliminary in vitro studies have been performed to assess the effect of experimental lipid emulsions of varying fatty acid composition on human adipose tissue metabolism. Subcutaneous human adipose tissue was obtained during elective surgery and placed in tissue culture. Physical mixtures of long chain triglyceride (LCT) and/or medium chain triglyceride (MCT) were added to the tissue culture medium so that the final concentration was 400 mg/dl. After a 3-day incubation period the tissue was harvested, placed in buffer and used to determine in vitro production of the prostaglandins prostacyclin I2 (measured as its stable endproduct 6-keto PGF1 alpha), thromboxane A2 (measured as TXB2), and prostaglandin E2. Measurements of the fatty acid profile found in the neutral- and phospholipid fraction of the adipose tissue and fat cell size were also made. The results demonstrate that samples incubated in 100% MCT had the most significant increase in prostaglandin production whereas those incubated in 100% LCT had the most significant decrease in activity of the three prostaglandins assayed, when compared to controls. The addition of LCT to MCT caused a dose-related decrease in adipose tissue prostaglandin production. There were no significant changes in the profile of fatty acids found in the neutral- or phospholipid fraction of adipose tissue. The results indicate that the relative level of MCT/LCT incubated with human adipose tissue has a significant effect on prostaglandin production.
Effects of hypocaloric diet low in essential fatty acids on in vitro human adipose tissue prostaglandin production and essential fatty acid status.
Very-low-calorie, fat-free defined-formula diets have been routinely used to treat obese patients. However, the effect of feeding a defined-formula diet low or devoid of essential fatty acids (EFAs) on EFA metabolism has not been determined. The aim of this investigation was to determine the effect of 400 kcal/day of Optifast 70 on EFA metabolism as determined by serum and adipose tissue levels of omega-6 fatty acids and measurements of in vitro human adipose tissue prostaglandin production. Five obese subjects entered the study after 1 wk of weight maintenance and then were placed on 12 wk of weight reduction. Blood and tissue samples were obtained before and after 4, 8, and 12 wk of weight reduction. Subjects tolerated 12 wk of dieting without any adverse reactions and lost an average of 21.7 +/- 7.0 kg. There was no significant effect of weight reduction on the levels of linoleic or arachidonic acid found in adipose tissue. There was a significant decrease in adipose tissue prostaglandin production of prostacyclin I2, measured as 6-keto-PGF1 alpha, after 12 wk of weight reduction. There was no significant change in the levels of thromboxane A2, measured as TXB2. There was a significant increase in serum arachidonic acid levels with no change in linoleic acid levels. The results demonstrated that the use of a diet devoid of EFA had no significant effect on omega-6 EFA metabolism as measured by serum and tissue levels and the ability of adipose tissue to produce prostaglandins in vitro.
Cellularity of obese and nonobese human adipose tissue.
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