ABSTRACT The heat losses of 24 individually housed pigs (initial body weights 20·0 to 31·8 kg) were measured for periods of 7 days at environmental temperatures of 10, 20 and 30°C. Within each environmental temperature three levels of air movement, 3, 33 and 56cm/s, were applied for a 2- or 3-day period either in an increasing or decreasing order. Heat loss was dependent on the environmental temperature and level of air movement to which the animals were exposed. The decrease in total thermal insulation at the highest air movement was equivalent to reducing the air-ambient insulation to almost zero. In terms of its thermal effect a 5cm/s increase in wind-speed was equivalent to a 1°C decrease in temperature. The lower critical temperature increased with increase in air movement from 19° at 3cm/s to 25° and 30°C at 33 and 56cm/s, respectively. Between air movement rates of 33 and 56cm/s, a 1°C decrease in critical temperature resulted from a 5·3cm/s decrease in air movement. The effect of increasing air movement from 3 to 56cm/s was to increase the animal's maintenance energy requirements from 706 to 881 kJ/kg 0·75 per day at 10°C, from 490 to 715 at 20°C and from 517 to 625 at 30°C.
EDG receptors are a family of closely related G-protein-coupled receptors, so-called since the first family member to be cloned is encoded by an endothelial differentiation gene. Of the six family members identified, five use lysophospholipids as their endogenous ligands. The sixth receptor, EDG-6, remains an orphan. These receptors activate multiple secondary-messenger pathways involving coupling to Gi, Gq/11, and G12/13 trimeric guanine nucleotide-binding proteins and are thought to play an important role in cell growth, development and maintenance, and cytoskeletal-dependent changes. EDG receptors are expressed in most mammalian cells and tissues, each subtype having a distinct distribution pattern, raising the possibility of tissue-specific biological roles that could be explored in drug-discovery programs. In this study the distribution of EDG-receptor mRNA within the nervous system has been investigated. As seen in peripheral tissues, these receptors appear to be discretely localized within specific brain regions and cell types. For example, EDG-1, -3, -4 receptors are confined to neuronal cells, EDG-2 receptors to white matter tracts, while EDG-5 receptors appear to be expressed in various cell types, including neuronal cells, white matter tracts, and ependymal cells. EDG-6-receptor mRNA was not detected in the nervous system. Speculation as to the role of these receptors in physiological/pathophysiological processes, particularly those involving cell development, proliferation, maintenance, migration, differentiation, plasticity, and apoptosis can be made from such distribution studies. EDG receptors located in brain neuronal cells might, for example, influence apoptosis and be involved in cell rescue following ischemic damage or during the early stages of progressive neurodegenerative diseases. Those restricted to oligodendrocytes might play a crucial role in myelination and offer a potential target in the treatment of demyelinating diseases, such as multiple sclerosis. In order to explore the role of these receptors, it is necessary to identify selective compounds. To this end we have developed an agonist-induced [35S]GTP gamma S binding assay using an HEK cell line expressing a pertussis-toxin-insensitive human-EDG-2-receptor-rat-Gi alpha 1-fusion protein. Such as assay system overcomes the problems associated with the almost ubiquitous responsiveness of mammalian cells to lysophospholipid. This assay lends itself to high throughput application, opening up the possibility of identifying compounds to further probe the therapeutic potential of EDG receptor manipulation.
1. The heat losses and energy and nitrogen balances of pregnant gilts, and of their non-pregnant litter sisters (controls), were measured for periods of 7 d at feed intakes of 1.8 or 2 3 kg/d (20 or 30 MJ metabolizable energy (ME) respectively) at an environmental temperature of 20°. The measurements were made within three separate periods of gestation; 40–60 d (early), 60–80 d (mid) and 90–110 d (late). Values for ME intake, heat loss, energy retention (ER), protein deposition and fat deposition were determined for both the pregnant and control animals on each treatment. 2. When expressed per kg body-Weight 0.75 per d, there was little difference in heat loss between pregnant and non-pregnant animals and between pregnant animals at the different stages of gestation at any given ME intake. However, heat loss was higher at the higher ME intake. 3. ER vaned inversely with heat loss. The decrease in ME intake (kJ/kg body-Weight 0.75 per d) during pregnancy resulted in a decrease in ER so that the pregnant animals were in negative energy balance at the low feed intake during late gestation. From the relation between ER and ME intake, estimates of the maintenance energy requirement (ME m ) of 411 and 401 kJ/kg body-weight 0.75 per d were calculated, with corresponding partial efficiencies of energy utilization (k) of 0.74 and 0.68 for the pregnant and non-pregnant animals respectively. 4. For the pregnant animals, protein deposition was highest during mid-pregnancy and was relatively independent of level of feeding during mid- and late pregnancy. There was little difference in protein deposition between pregnant and non-pregnant animals at the high feed intake. At the low feed intake, the pregnant animals generally had a higher protein deposition than their non-pregnant litter sisters and this was entirely associated with the accretion in reproductive tissue. 5. Fat deposition depended on the level of feeding, and at any given ME intake was similar for pregnant and control animals. In late gestation the low level of feeding was insufficient to prevent the pregnant animals losing fat. It was calculated that at term these animals lost 140 g fat/d from maternal stores. 6. From the relation between ME intake and protein and fat deposition, estimates of ME, and the energetic efficiencies of protein (k,) and fat (k,) deposition were determined. There was little difference in ME, (422 and 420 kJ/kg body-weight 0.5 per d) and k, (0.88 and 0.90) between pregnant and non-pregnant animals respectively. However, the pregnant animals had a higher k, (0.69 compared with 0.49 for controls) and this reflected the higher rates of protein deposition associated with pregnancy. 7. The efficiency of energy deposition in the reproductive tissue was calculated to be 0.72.
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