Exercise- and hypoxia-induced anaerobic metabolism and recovery: a student laboratory exercise using teleost fish.

Anaerobic metabolism is recruited in vertebrates under conditions of intense exercise or lowered environmental oxygen availability (hypoxia), typically resulting in the accumulation of lactate in blood and tissues. Lactate will be cleared over time after the reoxygenation of tissues, eventually returning to control levels. Here, we present a laboratory exercise developed as part of an upper-level vertebrate physiology class that demonstrates the effects of exercise and hypoxia exposure on blood lactate in fish and the subsequent decrease in lactate during recovery. Typically, the results obtained by students demonstrate that both treatments cause significant increases in blood lactate concentrations (two to three times higher than control values) that decrease back to normal values within 3 h of recovery under normoxia. The procedures described are generally applicable to other fish species and provide an alternative to using humans or other mammalian species to investigate anaerobic metabolism.

Vertebrate osmoregulation: a student laboratory exercise using teleost fish.

Here, we describe a laboratory experiment as part of an upper-level vertebrate physiology course for biology majors to investigate the physiological response of vertebrates to osmoregulatory challenges. The experiment involves measuring plasma osmolality and Na+-K+-ATPase activity in gill tissue of teleost fish acclimated to water of differing salinity. We describe results obtained using the widely available goldfish (Carassius auratus) and a common baitfish, the Gulf killifish (Fundulus grandis). The procedures described are generally applicable to other fish species, and they provide an alternative to the experimental use of humans or other mammalian species to investigate osmoregulation mechanisms. In addition to reenforcing the conceptual material covered in lecture, this laboratory exercise trains students in a wide range of laboratory and analytical skills, such as calculating and performing dilutions, pipetting, tissue sampling and homogenizing, preparing standard curves, conducting enzymatic assays, and analyzing and interpreting results. Typical student results are presented and discussed, as are common experimental and conceptual mistakes made by students.

Cutaneous heat flux models do not reliably predict metabolic rates of marine mammals.

Heat flux models have been used to predict metabolic rates of marine mammals, generally by estimating conductive heat transfer through their blubber layer. Recently, Kvadsheim et al. (1997) found that such models tend to overestimate metabolic rates, and that such errors probably result from the asymmetrical distribution of blubber. This problem may be avoided if reliable estimates of heat flux through the skin of the animals are obtained by using models that combine calculations of conductive heat flux through the skin and fur, and convective heat flux from the surface of the animal to the environment. We evaluated this approach based on simultaneous measurements of metabolic rates and of input parameters necessary for heat flux calculations, as obtained from four harp seals (Phoca groenlandica) resting in cold water. Heat flux estimates were made using two free convection models (double-flat-plate and cylindrical geometry) and one forced convection model (single-flat-plate geometry). We found that heat flux estimates generally underestimated metabolic rates, on average by 26-58%, and that small variations in input parameters caused large variations in these estimates. We conclude that cutaneous heat flux models are too inaccurate and sensitive to small errors in input parameters to provide reliable estimates of metabolic rates of marine mammals.

The energy budget of captive Siberian hamsters, Phodopus sungorus, exposed to photoperiod changes: mass loss is caused by a voluntary decrease in food intake.

Unlike most nonhibernating small mammals, Siberian hamsters (Phodopus sungorus) undergo a pronounced mass loss, almost exclusively as white adipose tissues, in response to a switch from long- to short-photoperiod exposure. This mass loss can be caused by an increase in the rate of energy expenditure, a decrease in the rate of energy intake, or a decrease in assimilation efficiency. In order to determine how they relate to photoperiod-induced mass loss, we measured these energy budget components every 2 wk on 12 captive Siberian hamsters exposed to 8 wk of long photoperiod followed by 12 wk of short photoperiod. Body mass decreased shortly after short-photoperiod exposure. This was accompanied by an immediate decrease in the rate of energy intake and, after a 2-wk delay, by a decrease in the rate of energy expenditure. The overall cumulative decrease in energy intake (376 kJ) could account for the mass loss (249 kJ) observed during short-photoperiod exposure. Regression analyses indicated that only the rate of energy intake was significantly related to the rate of mass change. Therefore, we conclude that photoperiod-induced mass loss in Siberian hamsters is caused by a decrease in the rate of food intake, rather than by changes in energy expenditure or in assimilation efficiency.

Metabolic and hormonal changes during the molt of captive gray seals (Halichoerus grypus).

Body mass, resting metabolic rates (RMRs), and serum thyroid hormones concentrations of six captive gray seals (Halichoerus grypus) were measured at regular intervals before, during, and after the annual molt. Changes in body mass suggested that the animals had increased energy expenditures during the last stage of the molt. These were associated with significantly elevated RMRs during the molt, the increase being more pronounced in juveniles ( < or = 53%) than in adults ( < or = 17%). The increase in RMR probably reflects the cost of generating a new pelt or to sustain a high skin temperature. Serum total and free thyroxine concentrations were elevated for all animals during the molt, but only juveniles had elevated serum triiodothyronine concentration. The increase in thyroid hormones occurred only during the last stage of the molt, suggesting that the role of thyroid hormones during the molt may be to sustain rapid hair growth in the last stage of molt or to maintain elevated heat production, rather than to initiate hair growth.

Energy balance and facultative diet-induced thermogenesis in mice fed a high-fat diet.

The present study was aimed at studying energy balance in mice fed a high-fat diet. Albino mice were divided into three groups. One group had free access to the stock diet, whereas the two other groups consumed a high-fat diet. One of the high-fat fed groups was fed ad libitum, whereas the other was offered a restricted amount of the same diet so that its energy intake was comparable to the group of mice given the stock diet. Energy balance measurements, which included indirect calorimetry and carcass analysis, were performed. Brown adipose tissue (BAT) properties were also investigated. The results show that gains in both body weight and fat were higher in mice that had free access to high-fat diet than in mice fed the stock diet. In animals given a restricted amount of the high-fat diet, fat gain increased, whereas protein gain was reduced in comparison with animals fed the stock diet. Unrestricted access to the high-fat diet led to an increase in both energy intake and energy gain. As revealed by both slaughter and indirect calorimetry techniques energy expenditure was, in high-fat fed mice, 40% higher than in animals fed either stock or a restricted amount of high-fat diet. Nadolol was shown to suppress a large part of the elevated metabolic rate seen in mice fed an unrestricted high-fat diet. In those mice, BAT mitochondrial GDP binding was also increased. In summary, the present results confirm that adaptive diet-induced thermogenesis (DIT) develops in mice made hyperphagic by an energy-dense palatable diet.(ABSTRACT TRUNCATED AT 250 WORDS)