The Pig as a Model for the Study of Obesity and of Control of Food Intake: A Review

The use of the pig for studies of food intake and obesity is reviewed. Effects of ambient temperature and taste on food intake as well as satiety factors impicating both neural and hormonal mechanisms originating in the gastrointestinal tract are considered; the integration of information in the central nervous system for both internal and external sources is hypothesized. Special concerns of food intake controls in the neonate are discussed, including effects of neonate sweet preference on food intake, gastrointestinal satiety factors, and hypoglycemia as a stimulus for food ingestion.For obesity studies, pigs offer several advantages, including their general physiological similarity to humans, similar fat cell size, and body fat distribution. Lipogenesis, lipolysis, and lipid mobilization are under intensive study in swine and the information obtained may have important application in studies of human obesity. The voluminous literature on metabolic differences between genetically lean versus obese populations of pigs suggests possibilities for application in humans. Greater characterization of differences and similarities between pigs and humans in important metabolic parameters related to regulation of food intake and obesity should facilitate better understanding and control of human obesity.     

Adipose tissue in the mammalian heart and pericardium: structure, foetal development and biochemical properties

1. The occurrence and relative abundance of adipose tissue around the heart and in the pericardium of wild and domesticated mammals are reviewed and some new data reported. 2. For macaque monkeys and a wide range of other adult mammals, the mean volume of epicardial adipocytes is constant at about half the average of that of other depots, although the relative mass of this depot is unrelated to the abundance of adipose tissue in the rest of the body. 3. In young adult guinea-pigs, the maximum rate of fatty acid synthesis is significantly higher in epicardial adipose tissue than that in the pericardial, perirenal and popliteal depots. 4. The rate of fatty acid release by epicardial adipose tissue is approximately twice that of the pericardial and perirenal depots. 5. The protein contents of guinea-pig epicardial and pericardial adipose tissue are similar, and are significantly higher than those of the perirenal and popliteal adipose tissue and there are no site-specific differences in the abundance of mitochondria. 6. In adult Macaca monkeys, the capacity of the epicardial adipose tissue for glucose utilization is about half that of the intra-abdominal depots. 7. The principal difference between epicardial adipose tissue and that elsewhere in the body is its greater capacity for fatty acid release. 8. It is suggested that cardiac adipose tissue may act as a local energy supply for adjacent myocardium and/or as a buffer against toxic levels of free fatty acids.     

The anatomy of adipose tissue in captive Macaca monkeys and its implications for human biology

In a sample of 31 sedentary, ad libitum-fed monkeys, most specimens had less than 5% adipose tissue by weight. Total fatness correlated closely with the number of adipocytes per kilogram lean body mass, but not at all with mean adipocyte volume, except in specimens below 5% fat. The total number of adipocytes per kilogram of lean body mass increased more than tenfold in the most obese specimens. These data suggest that, like humans but in contrast to laboratory rodents, adipocyte proliferation, not adipocyte enlargement, is the chief mechanism of adipose tissue expansion except in very lean monkeys. Adipose tissue was found in all the typical mammalian depots and in the superficial abdominal paunch, which enlarged disproportionately in obese specimens, forming an almost continuous layer over most of the body. Site-specific differences in the activities of some glycolytic enzymes were similar to those of other mammals. Adipocytes in the paunch depot showed biochemical properties in common with those in the groin depots. The distribution and cellularity of adipose tissue in normal humans were similar to those of exceptionally obese monkeys. Many of the interspecific and sex differences can be attributed to the much greater abundance of adipose tissue in humans, and may not be associated with hair reduction or aquatic habits. Some minor changes in the size or shape of certain adipose depots may have arisen recently under sexual selection. The relevance of laboratory rodents as animal models of human obesity is assessed from comparison of the cellular structure, anatomical distribution and enzyme profiles of adipose tissue in monkeys with those of human and other mammals.     

The effects of exercise and dietary restriction on the activities of hexokinase and phosphofructokinase in superficial, intra-abdominal and intermuscular adipose tissue of guinea-pigs

1. The activities per gram of adipose tissue of hexokinase and phosphofructokinase were higher in the centre two intermuscular adipose depots of guinea-pigs than in any of the seven superficial and intra-abdominal depots studied. 2. The capacity for glucose utilization was reduced following about 3 months of regular exercise in all adipose depots studied except in the popliteal depot. The proportion of lipid decreased, and that of protein increased, in this intermuscular depot following regular, strenuous exercise, but it did not enlarge disproportionately. 3. We suggest that certain intermuscular adipose depots may act as a local energy source for adjacent muscles. The anatomical relations of adipose tissue to muscle may be an integral part of its physiological function.     

Initiation of flight and pre-flight behaviour of anisopterous dragonflies Aeshna spp.

The start of flight of mature adult dragonflies (Aeshna spp.) was investigated using electrophysiological and photographic techniques already described. Flight begins with either an upwards or a downwards movement of the wings. Neuromuscular activity and wing vibrations resembling ‘warm-up’ in moths is reported in two species of Aeshna.     

Somatic embryogenesis in white spruce (Picea glauca): genetic control in somatic embryos exposed to storage,maturation treatments,germination, and cryopreservation

Genetic controls for growth of embryogenic cultures, storage, maturation treatments, germination and cryopreservation in white spruce somatic embryogenesis (SE) were examined. These SE processes were under genetic control but less strongly so than the initiation phase. For all the SE characters examined, variance due to clones within families was significant and often the largest genetic component of variance. This was further partitioned using an additive-dominance-epistasis model. A relatively-large proportion of the total genetic variance was due to epistatic variance in the maturation and germination of somatic embryos. Embryogenic lines were cryopreserved easily without a distinct genetic influence being noticed.     

Ontogenetic changes in the mechanical properties of the femur of the polar bear Ursus maritimus

The mechanical properties of the bone material of femora of five wild polar bears, ranging in age from three months to seven and three-quarter years, were compared with those of humans and axis deer. There are changes in mechanical properties in all three species with age, but their time course and extent vary greatly between species. The age-related changes in mechanical properties are attributable mainly to changes in mineralization. At any age, the properties of the polar bear's bones lie between those of humans and the deer. The architecture of the bear's bones, and the mechanical properties of their bone material, were related to the weight of the bears. The calculated stresses in the bones, and their deflection under load, were relatively constant compared with the very large differences in the weights of the bears and the sizes of their bones.