Origin of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 279

11
Origin of Energy Metabolism Impairments
Odile Dedourge-Geffard, Frédéric Palais, Alain Geffard, and Claude Amiard-Triquet
CONTENTS
11.1 Introduction ........................................................................................................................ 279
11.2 Food Availability and Quality in Polluted Media ........................................................ 280
11.3 Impairments of Food Uptake ........................................................................................... 282
11.4 Responses of Digestive Enzyme Activities to Chemical Stressors ............................. 285
11.5 Responses of Digestive Enzyme Activities to Factors Other than Contaminants ... 292
11.5.1 Modulation according to Quality/Quantity of Alimentary Resources ......... 292
11.5.1.1 Aquatic Vertebrates: Fish Examples ..................................................... 292
11.5.1.2 Aquatic Invertebrates ............................................................................. 293
11.5.2 Modulation according to Ontogenesis, Life Cycle, or Sex of Organisms ...... 294
11.5.2.1 Aquatic Vertebrates: Fish Examples ..................................................... 294
11.5.2.2 Aquatic Invertebrates ............................................................................. 295
11.5.3 Modulation according to Physicochemical Properties of Water:
Light, Salinity, Temperature ................................................................................. 296
11.6 Digestive Enzyme Activities in Environmental Biomonitoring ................................. 297
11.7 Perspectives ........................................................................................................................ 299
References ..................................................................................................................................... 299
11.1 Introduction
All biochemical and physiological processes in the life of organisms depend strictly on
their energy metabolism. Organisms obtain the energy necessary for life from an external
source, in the form of light energy in the case of autotrophic organisms or in the form
of chemical energy contained in food for heterotrophic organisms. In the case of hetero-
trophic organisms, the obtaining of energy is controlled by feeding and the subsequent
breakdown of food to release the energy contained (assimilation) (Figure 11.1). Feeding is
controlled by two categories of factors: on one hand the availability of food species, and
on the other the capacity of the feeder to capture and to consume this food. Decrease in
feeding can result either from an avoidance behavior toward a food recognized as con-
taminated or from physiological disturbance limiting, for example, locomotory activity.
Once ingested, food is subjected to the action of enzymes, by the process of digestion,
which represents all the processes by which raw food (containing carbohydrates, proteins,
lipids) is transformed into smaller molecules available for absorption.
The liver and the pancreas of vertebrates as well as the digestive gland or hepatopancreas
of mollusks and crustaceans play important roles in the digestion of food, by synthesizing
and by secreting digestive enzymes. However, these organs may also be the target of the
279