Aerobic and anaerobic swimming performance of individual Atlantic cod

Individual Atlantic cod (Gadus morhua) were exercised using three different measures of swimming performance. (1) An endurance test (critical swimming speed, U(crit), protocol) designed to assess predominantly aerobic endurance swimming (duration hours). (2) An acceleration test (U(burst)), in which the fish were required to swim against a rapidly increasing current until exhausted (duration minutes). This test was designed to assess predominantly glycolytic-based swimming capacity. (3) A sprint test that examined the animals' ability to swim away from a sudden stimulus (duration seconds). Rates of oxygen consumption (mdot (O2)) during the endurance test and various morphological variables of the individual fish were also measured. Both aerobic and anaerobic swimming performance of individual cod were found to be significantly repeatable over a 3 month period. mdot (O2) during the U(crit) protocol was also significantly repeatable at intermediate to high swimming speeds, but not at low speeds. Our results support extrapolation from metabolic rates at incremented swimming speeds to zero activity as the best way to measure standard metabolic rate in cod. While performance in the U(crit) test and the sprint test were positively correlated, there was a negative correlation between performance in the U(crit) test and performance in the U(burst) test. This implies a potential trade-off in individual cod between stamina and the ability to use glycolytic-based locomotion. Inter-individual variation in swimming performance during these protocols, while substantial, was not correlated with individual variation in fin surface areas, age or morphology. However, U(burst) performance was dependent upon the sex of the animals, while performance during the U(crit) protocol was significantly correlated with their aerobic scope for activity.

Leptin: an essential regulator of lipid metabolism

This paper reviews the general mechanisms by which leptin acts as a regulator of lipid reserves through changes in food intake, energy expenditure and fuel selection, with an emphasis on its direct effects on cellular lipid metabolism. Briefly, when leptin levels increase, food consumption decreases via modulation of hypothalamic neuropeptides. As well, normal decreases in energy expenditures (e.g. with diurnal cycles or reduced caloric intake) do not occur. This is probably caused by an increase in mitochondrial proton leak mediated by leptin via increases in sympathetic nervous system stimulation and thyroid hormone release. The decrease in caloric input coupled with relatively higher energy expenditure, therefore, leads to negative energy balance. Leptin also changes the fuel source from which ATP is generated. Fuel preference switches from carbohydrate (glucose) to lipid (fatty acids). This effect arises through stimulation of triacylglycerol catabolism by leptin. In vitro studies show that leptin is a potent stimulator of lipolysis and fatty acid oxidation in adipocytes and other cell types. Consequently, leptin is also a regulator of cellular triacylglycerol content. Hormonal regulation of leptin, as well as its role in fasting and seasonal weight gain and energy expenditure are also briefly discussed.

Beyond U(crit): matching swimming performance tests to the physiological ecology of the animal, including a new fish 'drag strip'

Locomotor performance of animals is of considerable interest from management, physiological, ecological and evolutionary perspectives. Yet, despite the extensive commercial exploitation of fishes and interest in the health of various fish stocks, the relationships between performance capacity, natural selection, ecology and physiology are poorly known for fishes. One reason may be the technical challenges faced when trying to measure various locomotor capacities in aquatic species, but we will argue that the slow pace of developing new species-appropriate swim tests is also hindering progress. A technique developed for anadromous salmonids (the U(crit) procedure) has dominated the fish exercise physiology field and, while accounting for major advances in the field, has often been used arbitrarily. Here we propose criteria swimming tests should adhere to and report on several attempts to match swimming tests to the physiological ecology of the animal. Sprint performance measured with a laser diode/photocell timed 'drag strip' is a new method employing new technology and is reported on in some detail. A second new test involves accelerating water past the fish at a constant rate in a traditional swim tunnel/respirometer. These two performance tests were designed to better understand the biology of a bentho-pelagic marine fish, the Atlantic cod (Gadus morhua). Finally, we report on a modified incremental velocity test that was developed to better understand the biology of the blacknose dace (Rhinichthys atratulus), a Nearctic, lotic cyprinid.

Glycerol and fatty acid kinetics in rainbow trout: effects of endurance swimming

Continuous infusions of 2-[3H]glycerol and 1-[14C]palmitate were performed in vivo in rainbow trout to measure the effects of prolonged swimming on (1) the rate of appearance of glycerol (Ra glycerol or lipolytic rate), (2) the rate of appearance of non-esterified fatty acids (Ra NEFA) and (3) the rate of triacylglycerol:fatty acid cycling (TAG:FA cycling or re-esterification). Our goals were to test the hypothesis that sustained exercise for up to 4 days causes the progressive mobilization of triacylglycerol reserves to supply fuel to contracting muscles, and to assess whether TAG:FA cycling plays a role in the regulation of NEFA availability in teleosts. Contrary to expectation, the rates of lipolysis and fatty acid release in resting trout are not affected by endurance exercise. Unlike mammals, which increase the rate of lipolysis by two- to fourfold during submaximal exercise, these active teleosts do not mobilize triacylglycerol reserves beyond resting levels to supply more NEFAs to working muscles. Furthermore, they maintain Ra glycerol and Ra NEFA well in excess of oxidative fuel requirements even at rest. More than two-thirds of the NEFAs produced are re-esterified, but the results show that TAG:FA cycling is not involved in the regulation of NEFA availability during or after swimming. We propose that the observed high rates of re-esterification represent an important feature of ectothermic metabolism that allows the restructuring of membrane phospholipids to be synchronized with frequent changes in body temperature.

High-altitude acclimation increases the triacylglycerol/fatty acid cycle at rest and during exercise

High-altitude acclimation alters lipid metabolism during exercise, but it is unknown whether this involves changes in rates of lipolysis or reesterification, which form the triacylglycerol/fatty acid (TAG/FA) cycle. We combined indirect calorimetry with [2-(3)H]glycerol and [1-(14)C]palmitate infusions to simultaneously measure total lipid oxidation, lipolysis, and rate of appearance (R(a)) of nonesterified fatty acids (NEFA) in high-altitude-acclimated (HA) rats exercising at 60% maximal O(2) uptake (VO(2 max)). During exercise, relative total lipid oxidation (%VO(2)) equaled sea-level control (SL) values; however, acclimation greatly stimulated lipolysis (+75%) but had no effect on R(a) NEFA. As a result, TAG/FA cycling increased (+119%), due solely to an increase in recycling (+144%) within adipocytes. There was no change in either group in these variables with the transition from rest to exercise. We conclude that, in HA, 1) acclimation is a potent stimulator of lipolysis; 2) rats do not modify TAG/FA cycling with the transition to exercise; and 3) in normoxia, HA and SL derive the same fraction of their total energy from lipids and carbohydrates.

Novel isosorbide-based substrates for human butyrylcholinesterase

Butyrylcholinesterase [EC 3.1.1.8] present widely in mammalian tissue does not have a precisely defined biological function or known endogenous substrate. However, it plays an important role in the detoxification of certain xenobiotics and is an established vector for the systemic liberation of other drugs from their prodrugs. While investigating a series of isosorbide-based prodrugs, we discovered that BuChE catalyses the hydrolysis of esters of the simple sugar isosorbide with unusually rapidity and in some cases with remarkable regioselectivity. In this study, a series of isosorbide esters were synthesised and their rates of hydrolysis measured by HPLC following incubation in diluted plasma solution. In general, little hydrolysis of the 5-ester group could be observed but the 2-ester group was usually hydrolysed very rapidly and the hydrolysis rate exhibited an unusual dependence on the identity of the 5-group. The results indicate that while the 5-ester group is not itself hydrolysed it is important for productive binding in isosorbide diesters.