Poikilothermic animals

The rate of free fatty acid production in the mammalian brain correlates to the extent of resistance to ischemia. FFA production rate is much lower in the brains of neonatal mammals and poikilothermic animals, organisms that display a greater resistance to cerebral ischemic insults than mature mammals [63]. In addition, within the mammalian brain, FFA release is higher in the gray matter compared with white matter, and there is a greater accumulation of AA in areas of the brain, such as the hippocampus, selectively vulnerable to cerebral ischemic damage. 

Metabolism - a final factor in need of comparative studies is the metabolism of xenobiotics. One obvious difference between mammalian and fish species is that their bodies usually function at temperatures at least 10°C different. This fact undoubtedly explains some differences in metabolic rate but even when in vitro incubations are run at optimal temperatures there is a 10 - 100 fold higher rate of mammalian vs. fish metabolism (14, 15). In other words, the level of the xenobiotic-metabolizing capacity, especially for oxidative pathways, of the poikilothermic animals is considerably lower than that of the homeothermic species. Elsewhere in this volume Dr. Bend has focused on this aspect of the handling of xenobiotics by fish (16). 

The close inverse relationship between ambient temperature and the percentage of polyunsaturated fatty acids in the lipids of poikilothermic animals has been confirmed by many research workers (Johnston and Roots, 1964 Ackman and Eaton, 1966 Knipprath and Mead, 1966 Jangaard et al., 1967 Roots, 1968 Morris and Schneider, 1969 Caldwell and Vemberg, 1970 Kemp and Smith, 1970 Baldwin, 1971 Hazel, 1972 Lynen, 1972 Viviani et al., 1973 Ota and Yamada, 1975 Patton, 1975 Bolgova et al., 1976 Deng et al., 1976 Driedzic et al., 1976 Irving and Watson, 1976 Leslie and Buckley,... 

Glushankova, M.A. (1967). Ambient temperature and thermoresistance of acto-myosin, alkaline phosphatase and adenylate kinase of poikilothermal animals (In Russian). In Variability of Cell Resistance in Animals at Auto- and Phylogenesis (B.P. Ushakov, ed.), pp. 126-141. Nauka, Leningrad. 

FIGURE 3 Effect of temperature and food availability on food consumption (Ac) and the partitioning of consumed food for various purposes by a poikilothermic animal. The curves are qualitative and purely theoretical. [Reprinted with permission from Warren, C. E. (1971). Biology and Water Pollution. Saunders, Philadelphia. 1971 by W B. Saunders Co.]... 

If diet and hormones are important in the regulation of A6 desaturation activity as a means to increase or decrease polyunsaturated acid biosynthesis along the day cycle not less important is the modification of the activity of the enzyme along the life span (Brenner, 1974) or in different environmental condition to adapt the cell to the new situations. The decrease of A9 desaturase activity of liver or testis with age has been proved (Brenner, 1974). In poikilothermic animals like fish the specific activity of the A6 desaturase increases with a decrease of the environmental temperature. This increase compensates the diminished velocity of the reaction due to the low temperature (Torrengo and Brenner, 1976). 

Sometimes there is confusion due to different use of terms. Thermodynamics calls a process exothermic when heat is given off by the system and endothermic when it consumes heat. In biology, warm-blooded (homeothermic) animals like mammals and birds that produce heat to keep their body temperature constant are called endotherms and their behaviour endothermic, in contrast to the thermodynamical direction. Their counterparts with changing body temperatures are ecto-therms (not exotherms) or cold-blooded poikilothermic) animals. Nevertheless, all of them produce heat as a by-product of their metabolism so that they can be monitored by (exothermic) calorimetry. 

Unsaturations of lipids play a key role in lipid homeostasis, where organisms adapt to temperature variations of the environment. Plants and animals maintain physiological functions by reversibly altering the composition and conformation of lipid molecules of the cell membrane. To achieve this, they extensively and elegantly use the unsaturations (double bonds) present in their side chains. This is the process by which cell membranes adjust their flexibility (fluidity) of the bilayer and adapt themselves to perturbations in temperature, pressure, and other variations in the natural environment [11-14]. They remain indispensable for the poikilothermism exhibited by fishes, invertebrates, and amphibians [15, 16]. Commercially,... 

Adverse effects of fenvalerate on survival of terrestrial arthropods were observed at 0.002 to 0.015 pg whole-body topical application, O.llkg/ha aerial application, 5.4 mg/kg in the soil, 50 mg/kg in the diet, and 1.4 g/ant mound (Table 20.4). Synthetic pyrethroids are more effective in biological systems at low temperatures. The relative sensitivity of insects when compared with mammals is attributed in part to this negative temperature coefficient. Thus, warm-blooded animals are less affected than insects and other poikilotherms (Klaassen etal. 1986). Fenvalerate, for example, showed a negative correlation between temperature and toxicity to crickets (Acheta pennsylvanicus), being up to 1.9 times more toxic at 15°C than at 32°C (Harris etal. 1981). A similar case is made for honey bees (Apis mellifera) (Mayer et al. 1987) and for many species of aquatic invertebrates and fish (Mayer 1987). 

The ability of some organisms to control the pH and temperature of their cells and tissues represents a major biological development. Homeothermic animals (e.g. mammals) maintain a constant temperature of about 37 °C as this corresponds to the temperature of optimum activity of most enzymes. Poikilothermic or so-called cold-blooded animals (e.g. reptiles) have to sun themselves for sometime every morning in order to raise their body temperature in order to optimize enzyme activity within their cells. 

The concept of temperature compensation of metabolism at the whole animal level in poikilotherms has been subject to strong criticism by Holeton (1974, 1980) and especially by I.V. Ivleva (1981), who believed that such compensation was an artefact arising from inadequate acclimation. However, Ivleva s own experiments were carried out on aquatic invertebrates, not fish, and the data referred to standard metabolism rather than total or active. Note that total metabolism is that taking place in an animal in nature, active metabolism is that which supplies locomotory activity, standard metabolism is that observed in experiments, and basal metabolism is that in the resting state. Ivlev (1959) found that apparent adaptive reactions of animals are seen mostly in active, not standard or basal, metabolism. However, more recent work (Karamushko and Shatunovsky, 1993 Musatov, 1993) appears rather to favour the concept of I.V. Ivleva, that standard, not active, metabolism illustrates the adaptive reactions. 

Harshbarger, J.C., and C.J. Dawe Hematopoietic Neoplasms in Invertebrate and Poikilothermic Vertebrate Animals. In Unifying Concepts of Leukemia, Bibl. haemat. No. 39, (Dutcher, R.M., and L. Chieco-Bianchi, eds.), p. 1. Basel Karger. 1973. 

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