PubMed Health⌕ Search

Biomedical subjects

J Kirtland

Publications and source records attributed to J Kirtland.

11 recordsLinked to original sources
PubMed1999

The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth.

During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5-50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9+/-7.3 to 126.2+/-23.1 W m(-)(2) and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0+/-2.6 beats min(-)(1), N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.

Animals↗
PubMed1981

Body lipids of guinea pigs exposed to different dietary fats from mid-gestation to 3 months of age. IV. Effect of food restriction at 3 months on the distribution and cellularity of adipose tissue.

Pregnant guinea pigs were fed one of three diets: a control low-fat diet or a high-fat diet containing maize oil or beef tallow. Offspring were reared on the same diets as their mothers. At 12 weeks of age some animals were killed; others had their food intake restricted for 2 weeks and were then killed. Body weight, weight of various adipose tissue depots and size and number of fat cells were measured. All adipose depots decreased in weight during food restriction and fat cell size was reduced. Perirenal adipose tissue lost the greatest amount of weight and the gonadal depot the least. Fat cell number of females was unaffected by food restriction, whereas in males the number of observable fat cells decreased in the perirenal depot. Previous diet influenced the amount of body weight lost during food restriction. Animals fed beef tallow lost less weight than those fed maize oil. Possible reasons are discussed.

Adipose Tissue↗
PubMed1980

Changes in adipose tissue of the rat due early undernutrition followed by rehabilitation. 3. Changes in cell replication studied with tritiated thymidine.

1. Well-nourished rats were injected with tritiated thymidine at 15, 22, 28 or 84 d of age. At 1, 6, 11 and 16 d after injection animals from each group were killed, samples of adipose tissue were removed from two subcutaneous sites (abdominal and scapular) and separated, using collagenase (EC 3.4.24.3), into 'fat cell' and 'stromal cell' fractions. The specific (radio)activity of DNA isolated from each fraction was measured. The specific activity of DNA isolated from two 'deep body' sites (perirenal and epididymal) was measured only in the animals injected at 84 d of age. 2. Animals undernourished from birth up to 84 d of age were injected with tritiated thymidine at 22, 28 or 84 d of age. Animals were killed 1 and 11 d after injection, adipose tissue removed, and the specific activity of DNA measured. Other undernourished animals were rehabilitated from 84 to 107 d and injected at 91 d of age with tritiated thymidine. The animals were killed 1, 6, 11 and 16 d after injection, adipose tissue was removed from the subcutaneous and deep body sites and the specific activity of DNA determined as before. 3. In well-nourished animals fat cell replication had largely ceased by 12 weeks of age in the subcutaneous depots. There were differences between the various sites of adipose tissue regarding the period of hyperplastic growth, its timing or rate of replication or both. 4. In undernourished animals replication was slow in the subcutaneous depots compared with well-nourished animals of the same age. Rehabilitation from undernutrition stimulated replication which resulted in higher rates in all four depots examined compared with those in well-nourished animals. 5. The findings are discussed in relation to the concept of a finite period of hyperplasia for adipose tissue.

Adipose Tissue↗
PubMed1977

The consequences of early overnutrition for fat cell size and number: the pig as an experimental model for human obesity.

(1) The objectives of these studies were: (a) to determine the period during which fat cells were being formed in different fat depots in the pig; (b) to discover whether total fat cell number could be affected by overfeeding from weaning or later in life, and (c) to examine the domestic pig as a model for human obesity studies especially as to the influence of the energy intake at different stages in life on fat cell size and number. (2) Pigs were weaned at six weeks of age and allocated to one of four diets. Group H was fed to appetite on a high carbohydrate diet and became extremely obese. Group L was fed at half the energy intake of group H; these animals grew steadily but deposited little adipose tissue. Group L-H was fed as group L for 40 weeks and then as group H for the rest of the experiment, while group H-L was fed as group H for 40 weeks and then placed on a very restricted ("slimming") diet for the remainder of the experiment. (3) The volume of fat cells in group H was about four-fold greater than in group L at the end of the experiment. Cell volume increased rapidly when group L was fattened after 40 weeks and could be reduced significantly, albeit slowly, when group H was "slimmed". (4) There was a significant increase in the apparent number of fat cells in the depots of overfed pigs that did not diminish when the animals were "slimmed". However, in restricted pigs subsequently fattened, there was an apparent steady increase in fat cell number that eventually reached the same figure as in pigs overfed from weaning. (5) The standard methodology is inadequate to make broad generalizations about the influence of diet on cellularity. First, the development of fat cell size and number follows different time scales in different depots. It is essential to monitor several sites before attempting to estimate cell number. Secondly, since cells with diameters less than about 15 micrometer are not detected, "empty" cells, containing no fat, may be present from birth: subsequently they may be filled when energy intake is appropriate so that later they become visible, and are recorded as fat cells. In these cases there will be an "apparent" but not a real increase in cell number.

Adipose Tissue↗
PubMed1976

Body lipids of guinea pigs exposed to different dietary fats from mid-gestation to 3 months of age.

Pregnant guinea pigs were fed one of three diets: a control low-fat diet, or a high-fat diet containing maize oil or beef dripping. At birth some animals were killed and the remainder reared on the same diet as their mothers till 3 months old. Body weight, weight of various adipose tissue depots, size and number of fat cells were measured. Animals fed high-fat diets were fatter than control animals. On all diets females were fatter than males. In both instances the increase in adipose tissue mass was attributable to enlargement of fat cells. The composition of dietary fat had little influence on the cellularity of adipose tissue.

Adipose Tissue↗
PubMed1976

Body lipids of guinea pigs exposed to different dietary fats from mid-gestation to 3 months of age. III. The fatty acid composition of the lipids of plasma, adipose tissue, liver and muscle at 3 months of age.

Pregnant guinea pigs were fed one of three diets: a 'control' low-fat diet, or a high-fat diet containing maize oil or beef dripping. Offspring were reared on the same diet as their mothers and when they were 3 months old, fatty acid compositions of the lipids of the adipose tissue, blood plasma, liver and muscle were analysed. The proportion of linoleic acid was elevated in both the storage triglycerides and the tissue phosphoglycerides of animals fed 'maize' diet whereas in the 'beef' group the proportion of oleic acid was significantly elevated compared with controls. A substantial part of these diet-induced changes in tissue fatty acid composition had occurred by the time animal was born; only minor changes took place in the subsequent 3 months of feeding.

Adipose Tissue↗