Effect of hunger on the drinking behaviour of rodents adapted for mesic and xeric environments

Observations of drinking behaviour were taken on six rodent species during fasting. Four of these species were wild-caught and had not previously been examined for food deprivation polydipsia (FDP). These data support an hypothesis that a negative correlation exists between water availability in the natural habitat and the occurrence of FDP. Namely, xerophilous species exhibit an absolute polydipsia during food deprivation while mesically adapted species evidence depressed water consumption. Urine analyses during food deprivation indicated substantial decreases in electrolyte and osmotic pressure concentrations in all species. The drinking patterns of the three desert species investigated are discussed with reference to the availability of green vegetation in the natural habitat; however, there is presently no explanation for the observed polydipsia.     

Nitrogen availability affects hydraulic conductivity of rice roots,possibly through changes in aquaporin gene expression

Background and aims

Nitrogen (N) availability affects water uptake from the roots, which decreases upon N deprivation and increases upon resupply. The aim of this study was to reveal possible mechanisms of regulation of water transport in roots through physiological and morphological adaptations to N availability.

Methods

The effects of continuous N deprivation and following resupply on root morphology, osmotic hydraulic conductivity, and expression of genes for aquaporins (water channels) were examined in rice (Oryza sativa L.) plants. The effect of local N availability was examined by using a split-root system.

Results

N deprivation decreased the expression of root-specific aquaporin genes, whereas N resupply increased their expression. Changes in aquaporin gene expression were correlated with changes in hydraulic conductivity. N deprivation increased dry matter allocation to the roots. In a split-root experiment, the expression of root-specific aquaporin genes was down-regulated in the N-deprived half, whereas it was up-regulated in the N-supplied half.

Conclusion

Our results suggest that expression of genes for root-specific aquaporins underlies the changes in conductivity during continuous N deprivation and resupply. Rice plants seem to adapt to N availability through coordinated adjustment of root proliferation and abundance of aquaporins.     

Metabolic and endocrine effects of water and/or food deprivation in rats

Metabolic and endocrine effects of water and/or food deprivation in rats. We aim at studying the effect of water deprivation, food deprivation and their combination for three days on adrenal cortex, pituitary-thyroid axis and vasopressinergic system activity in rats. Corticosterone level was determined by fluorimetric method. The levels of free thyroxine (FT4) and thyroid stimulating hormone (TSH) were determined by immunoenzymatic assay and vasopressin (AVP) level was determined by radio-immunoassay. In all three groups, basal levels of plasma corticosterone were increased. A thyroid dysfunction was shown after water deprivation, food deprivation and their combination reflected by a significant decrease in FT4 levels. Paradoxically, a significant decrease in TSH level was observed in food-deprived rats and in rats subjected to simultaneous food and water deprivation, while a slight and not significant decrease in TSH level was shown in water-deprived rats. A significant increase in plasma AVP level was observed after water deprivation and simultaneous water and food deprivation, while no change was found after food deprivation. The data indicated that water deprivation, food deprivation and their combination stimulated the adrenal cortex, thereby suggesting a stress state. On the other hand, it seems that nutritional stress modifies the pituitary-thyroid axis through mechanisms different from those of osmotic stress. Moreover, it seems that food deprivation partially prevented the stimulatory effect of water deprivation on vasopressinergic system.     

Expression of dehydrins under heat stress and their relationship with water relations of sugarcane leaves

The heat stress-induced dehydrin proteins (DHNs) expression and their relationship with the water relations of sugarcane (Saccharum officinarum L.) leaves were studied. Sugarcane seedlings were subjected to heat stress (day/night temperature of 40/35 °C) under relative humidity 60/65 % to avoid aerial desiccation and determinations made at 4, 12, 24, 36, 48, 60 and 72 h. The leaves showed a sharp decline in the water and osmotic potentials, and relative water content during first 12 h of heat stress, but a regain in their values in 24 h. The pressure potential (ψ_p) decreased initially but increased later and approached control leaves. The increase in ψ_p was tightly correlated to the accumulation of free proline, glycinebetaine and soluble sugars, indicating their possible involvement in the osmotic adjustment under heat stress. Immunological detection revealed the expression of three DHNs with an apparent molecular mass of 21, 23 and 27 kDa under heat stress (48 to 72 h) and their expression was independent of the changes in the water relations of leaves.     

Water balance in Collembola and its relation to habitat selection: Water content,haemolymph osmotic pressure and transpiration during an instar

In the two collembolan species Orchesella cincta and Tomocerus minor the water content, haemolymph osmotic pressure and transpiration rate fluctuate with the feeding rhythm during each instar. The changes in water content, however, are due to changes in dry weight, because the absolute water weight stays constant during the instar.The intake of food is probably the cause of the increase in haemolymph osmotic pressure. Increase of osmotically active substances in the blood and/or blood volume reduction may be responsible for the rise in osmotic pressure. This change in osmotic pressure in turn may affect the responsiveness of the animals to water as well as their feeding behaviour.Changes in the epicuticle and in epidermal cell membranes may cause changes in the rate of transpiration. The high rate observed during ecdysis and during the mid-instar may explain the behaviour of the animals in varied water conditions.Dehydration during the instar causes an equivalent rise in osmotic pressure for both Tomocerus minor and Orchesella cincta. The water loss appears to involve the haemolymph. The physiological state of the animal does not influence the rise in osmotic pressure. There are no signs of any osmoregulation in the two species.     

Food deprivation in the common vole (<Emphasis Type="Italic">Microtus arvalis</Emphasis>) and the tundra vole (<Emphasis Type="Italic">Microtus oeconomus</Emphasis>)

Arvicolinae voles are small herbivores relying on constant food availability with weak adaptations to tolerate prolonged food deprivation. The present study performed a comparative analysis on the responses to 4–18 h of food deprivation in the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus). Both species exhibited rapid decreases in the plasma and liver carbohydrate concentrations during phase I of fasting and the decline in the liver glycogen level was more pronounced in the tundra vole. The plasma thyroxine concentrations of the common vole decreased after 4 h. Lipid mobilization (phase II of fasting) was indicated by the increased plasma free fatty acid levels after 8–18 (the common vole) or 4–18 h (the tundra vole) and by the elevated lipase activities. In the tundra vole, the plasma ghrelin concentrations increased after 12 h possibly to stimulate appetite. Both species showed increased liver lipid concentrations after 4 h and plasma aminotransferase and creatine kinase activities after 12–18 h of food deprivation implying liver dysfunction and skeletal muscle damage. No signs of stimulated protein catabolism characteristic to phase III of fasting were present during 18 h without food.     

Plasma renin activity, vasopressin concentration, and urinary excretory responses to exercise in men

Plasma vasopressin concentration (PAVP), renal function, and effectors of vasopressin release were evaluated in male volunteers during running at heart rates of 0, 35, 70, and 100% of maximum after 10 h abstinence from water (normal hydration) and at 100% after ingestion of 300 ml water. Plasma renin activity (PRA) and PAVP were linearly correlated and correlated to work intensity over all observations. Changes in PAVP were not correlated with changes in plasma osmolality (POSMOL) and plasma volume (PV) over all observations. Furthermore, despite similar changes in POSMOL, PV, PRA, body weight, mean arterial pressure, and plasma lactate concentration, the increase in PAVP after maximal exercise was greater during normal hydration than the water-supplemented state. Decreased urine flow observed in association with exercise was characterized by increased free water and decreased osmotic and creatinine clearances. Thus increased PAVP associated with exercise appears not to play a role in the concomitant antidiuresis. Vasopressin stimuli are probably variable at different times during exercise and may include factors other than those measured.     

Day-Night Variations in Malate Concentration, Osmotic Pressure, and Hydrostatic Pressure in Cereus validus

Malate concentration and stem osmotic pressure concomitantly increase during nighttime CO₂ fixation and then decrease during the daytime in the obligate Crassulacean acid metabolism (CAM) plant, Cereus validus (Cactaceae). Changes in malate osmotic pressure calculated using the Van't Hoff relation match the changes in stem osmotic pressure, indicating that changes in malate level affected the water relations of the succulent stems. In contrast to stem osmotic pressure, stem water potential showed little day-night changes, suggesting that changes in cellular hydrostatic pressure occurred. This was corroborated by direct measurements of hydrostatic pressure using the Jülich pressure probe where a small oil-filled micropipette is inserted directly into chlorenchyma cells, which indicated a 4-fold increase in hydrostatic pressure from dusk to dawn. A transient increase of hydrostatic pressure at the beginning of the dark period was correlated with a short period of stomatal closing between afternoon and nighttime CO₂ fixation, suggesting that the rather complex hydrostatic pressure patterns could be explained by an interplay between the effects of transpiration and malate levels. A second CAM plant, Agave deserti, showed similar day-night changes in hydrostatic pressure in its succulent leaves. It is concluded that, in addition to the inverted stomatal rhythm, the oscillations of malate markedly affect osmotic pressures and hence water relations of CAM plants.     

Brain serotonin turnover and plasma prolactin and growth hormone concentrations during changes in osmotic balance in the domestic fowl

Summary Young cockerels injected 24 h earlier with 0.9% saline,para-chorophenylalanine (pCPA, brain serotonin depletor) or alpha-methylpara-tyrosine (AMPT, brain catecholamine depletor) were deprived of access to water for 24 h. Plasma prolactin concentrations were markedly elevated by water deprivation and returned to normal on rehydration. pCPA, but not AMPT, significantly reduced the increase in prolactin. Concentrations of growth hormone were not affected by water deprivation. Brain serotonin concentrations were reduced by treatment with pCPA. Groups of cockerels were maintained under normal conditions or without access to drinking water for 12 h or 24h. Some were injected with the monoamine oxidase inhibitor pargyline, which increased the prolactin and decreased the growth hormone concentration in the plasma of the hydrated birds. The inhibitory effect of pargyline on growth hormone was augmented following water deprivation. Serotonin levels were not significantly affected by water deprivation but turnover (defined as accumulation of serotonin after pargyline treatment) was increased in the hypothalamus but not in remaining tissue. Injecting 30% saline solution intravenously markedly increased plasma prolactin whilst growth hormone concentrations were decreased. Serotonin turnover was increased in the hypothalamus but not in other brain regions. The results show that secretion of prolactin and growth hormone by the pituitary gland during osmotic imbalance in the fowl may be mediated by changes in hypothalamic scrotonin turnover.     

The effect of food and water deprivation on the peripheral blood parameters of the mouse

Various peripheral blood and bone marrow parameters were determined during food and water deprivation and during food deprivation alone in order to obtain base lines that may be used to make comparisons with similar data from irradiated mice. The peripheral blood parameters following food and water deprivation were similar to those following food deprivation alone. The mean survival time was about 5 days and the weight loss 40% of the control weight. There was an absolute decrease in the total circulating lymphocyte and platelet counts, while the total granulocyte count remained unchanged or increased. The blood volume decreased, while the hematocrit and specific gravity of the blood increased. The bone marrow parameters following food and water deprivation showed that erythropoiesis was more markedly depressed than myelopoiesis. The tritiated thymidine labeling index for granulopoietic cells and megakaryocytes decreased progressively during starvation. The variations in the white blood count and the bone marrow parameters are not comparable with those found in irradiated mice having the G.I. syndrome; the changes in mean survival time, weight loss, hematocrit, and blood volume are similar.     

Excitatory amino acids in rostral ventrolateral medulla support blood pressure during water deprivation in rats

Water deprivation is associated with regional increases in sympathetic tone, but whether this is mediated by changes in brain stem regulation of sympathetic activity is unknown. Therefore, this study tested the hypothesis that water deprivation increases excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), by determining whether bilateral microinjection of kynurenate (Kyn; 2.7 nmol) into the RVLM decreases arterial pressure more in water-deprived than water-replete rats. Plasma osmolality was increased in 48-h water-deprived rats (313 +/- 1 mosmol/kgH2O; P < 0.05) compared with 24-h water-deprived rats (306 +/- 2 mosmol/kgH2O) and water-replete animals (300 +/- 2 mosmol/kgH2O). Kyn decreased arterial pressure by 28.1 +/- 5.2 mmHg (P < 0.01) in 48-h water-deprived rats but had no effect in water-replete rats (-5.9 +/- 1.3 mmHg). Variable depressor effects were observed in 24-h water-deprived animals (-12.5 +/- 2.4 mmHg, not significant); however, in all rats the Kyn depressor response was strongly correlated to the osmolality level (P < 0.01; r2 = 0.47). The pressor responses to unilateral microinjection of increasing doses (0.1, 0.5, 1.0, and 5.0 nmol) of glutamate were enhanced (P < 0.05) during water deprivation, but the pressor responses to intravenous phenylephrine injection were smaller (P < 0.05). These data suggest that water deprivation increases EAA drive to the RVLM, in part by increasing responsiveness of the RVLM to EAA such as glutamate.     

Hydration effects of heparin on antithrombin probed by osmotic stress.

Antithrombin is a key inhibitor of blood coagulation proteases and a prototype metastable protein. Heparin binding to antithrombin induces conformational transitions distal to the binding site. We applied osmotic stress techniques and rate measurements in the stopped flow fluorometer to investigate the possibility that hydration changes are associated with these transitions. Water transfer was identified from changes in the free energy of activation, Delta G(++), with osmotic pressure pi. The Delta G(++) was determined from the rate of fluorescence enhancement/decrease associated with heparin binding/release. The volume of water transferred, Delta V, was determined from the relationship, Delta G/pi = Delta V. With an osmotic probe of 4 A radius, the volumes transferred correspond to 158 +/- 11 water molecules from reactants to bulk during association and 162 +/- 22 from bulk to reactants during dissociation. Analytical characterization of water-permeable volumes in x-ray-derived bound and free antithrombin structures were correlated with the volumes measured in solution. Volume changes in water permeable pockets were identified at the loop-insertion and heparin-binding regions. Analyses of the pockets' atomic composition indicate that residues Ser-79, Ala-86, Val-214, Leu-215, Asn-217, Ile-219, and Thr-218 contribute atoms to both the heparin-binding pockets and to the loop-insertion region. These results demonstrate that the increases and decreases in the intrinsic fluorescence of antithrombin during heparin binding and release are linked to dehydration and hydration reactions, respectively. Together with the structural analyses, results also suggest a direct mechanism linking heparin binding/release to loop expulsion/insertion.     

Responses of a CAM Plant to Drought and Rainfall: Capacitance and Osmotic Pressure Influences on Water Movement

Daily and seasonal patterns in water flow and water potentialwere investigated for the Crassulacean acid metabolism succulentAgave deserti during an extended summer drought and for a periodfollowing rainfall. Field measurements of transpiration andof osmotic pressure changes over selected 24 h periods wereused as input variables for a computer model of water flow thatwas based on an electrical circuit analog of the whole plant.Parameters such as root resistance and tissue capacitance werealso varied to reflect the effects of changing plant or soilwater status. The model predicted internal water flow and waterpotential during the drought cycle and was used to assess therole of tissue osmotic properties in water uptake from the soiland in internal water redistribution. For plants under wet soil conditions, 55% of the night-timetranspiration was derived from water storage, this storage beingrecharged during the day. As drought progressed, transpirationand the nocturnal increase in osmotic pressure declined, althoughthe osmotic pressure itself increased. The difference in osmoticpressure between the water storage tissue and the chlorenchymacaused a net flow of water into the chlorenchyma after 3 weeksof drought, thereby increasing chlorenchyma turgor pressure.Simulations also indicated that a large increase in root resistancemust occur to prevent substantial water loss from the plantto the dry soil. After rainfall, recharge of plant water storagewas complete within one week, although full recovery in theamplitude of daily osmotic pressure variations took longer. Key words: Agave deserti, transpiration, water potential, water storage     

The effects of food deprivation on beta-adrenergic responsiveness in male rats

Male rats were deprived of food for varying lengths of time (0-96 h) and their responses to beta-adrenergic stimulation with isoproterenol were tested. Food deprivation for 48 or 96 h attenuated the increase in tail skin temperature normally seen following administration of isoproterenol. The degree of attenuation was dependent on the duration of the deprivation period. Rats deprived of food for 96 h and then refed for 48, 96, or 144 h showed a return of tail skin temperature response to near normal levels. The increase in heart rate observed following administration of isoproterenol was also attenuated following 48 or 96 h of food deprivation. Again, the degree of attenuation was dependent on the duration of the deprivation period. Food deprivation for 96 h led to a decrease in basal plasma levels of T3, T4, and glucose. The increase in plasma glucose following administration of isoproterenol was also attenuated following 96 h of food deprivation. In contrast to the thermal, cardiac, and glucose responses, the dipsogenic response to isoproterenol was increased following food deprivation. The attenuation in beta-adrenergic responses observed in the food-deprived rats might help explain the effects of food deprivation on cold tolerance.     

Waking and Sleeping following Water Deprivation in the Rat

Wake-sleep (W-S) states are affected by thermoregulation. In particular, REM sleep (REMS) is reduced in homeotherms under a thermal load, due to an impairment of hypothalamic regulation of body temperature. The aim of this work was to assess whether osmoregulation, which is regulated at a hypothalamic level, but, unlike thermoregulation, is maintained across the different W-S states, could influence W-S occurrence. Sprague-Dawley rats, kept at an ambient temperature of 24°C and under a 12 h∶12 h light-dark cycle, were exposed to a prolonged osmotic challenge of three days of water deprivation (WD) and two days of recovery in which free access to water was restored. Two sets of parameters were determined in order to assess: i) the maintenance of osmotic homeostasis (water and food consumption; changes in body weight and fluid composition); ii) the effects of the osmotic challenge on behavioral states (hypothalamic temperature (Thy), motor activity, and W-S states). The first set of parameters changed in WD as expected and control levels were restored on the second day of recovery, with the exception of urinary Ca⁺⁺ that almost disappeared in WD, and increased to a high level in recovery. As far as the second set is concerned, WD was characterized by the maintenance of the daily oscillation of Thy and by a decrease in activity during the dark periods. Changes in W-S states were small and mainly confined to the dark period: i) REMS slightly decreased at the end of WD and increased in recovery; ii) non-REM sleep (NREMS) increased in both WD and recovery, but EEG delta power, a sign of NREMS intensity, decreased in WD and increased in recovery. Our data suggest that osmoregulation interferes with the regulation of W-S states to a much lesser extent than thermoregulation.     

Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent

Abstract Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24-h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one-third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.     

Morphological and biochemical effects of food deprivation during the early development of Pacific red snapper Lutjanus peru

We report the effects of food deprivation on the early development of Pacific red snapper Lutjanus peru during the first days of development. The point of no return (PNR) was determined using the feeding incidence after a delay in first feeding. The gradual deterioration of the larvae during food deprivation was recorded using morphometric, histological, enzymatic and biochemical analysis. The time to reach the PNR was 120 h after hatching. Morphologically, the total length, muscle height, head length, tail length and pectoral angle showed the biggest reductions and their growth coefficients changed significantly during food deprivation. Histologically, enterocyte height also was reduced significantly. The protein concentration and activities of the digestive enzymes trypsin, cathepsin-like and lipase showed a significant decrease; meanwhile, amylase activity remained constant during food deprivation. The concentration of total essential free amino acids (EFAAs) decreased significantly while that of the nonessential free amino acids (NEFAAs) remain stable during food deprivation. The most abundant EFAAs were lysine, leucine, isoleucine and valine; the most abundant NEFAAs were alanine, glycine and glutamate, suggesting a more prominent role as energy substrates. At the time of the PNR the concentration of almost all the free amino acids showed a significant decrease. Early food deprivation has a significant impact on the morphology and biochemical characteristics of L. peru. These results suggest that initial feeding of L. peru should begin within 3 days of yolk sac depletion to avoid the PNR. Further studies are necessary to confirm and validate the characters identified in this study as biomarkers of starvation under culture conditions and evaluate their possible utility in ichthyoplankton surveys.     

Effect of long and short photoperiod on vasotocin neurons of paraventricular nuclei and adrenal function of water deprived Japanese quail

The responses of magnocellular neurons of paraventricular nuclei (PVN) and changes to adrenal activity to water deprivation in Japanese quail maintained under gonado-inhibitory and stimulatory photoperiods were examined. Water deprivation of 4 days resulted in a 12% decrease in body weight of sexually regressed short day (SD, 6L:18D) quail, while the decrease was more (18%) in sexually stimulated long day (LD, 16L:8D) quail. The increase in plasma osmolality following water deprivation was also more (47%) in LD than to SD quail (36%). Under the LD condition, quail had increased numbers, sizes and immunostaining of ir-AVT neurons of PVN compared to SD condition. A significant increase in the number of ir-AVT neurons was observed following 4 days of water deprivation in both SD and LD quail compared to their respective fully hydrated controls. However, the degree of response was more under the LD compared to the SD condition suggesting that gonado-stimulatory long days increase the activity/response of the AVT system. Increased adrenal ascorbic acid content (i.e., activity) was also observed to quail of LD when compared to SD treatment. However, osmotic stress led to adrenal hypertrophy and hyperactivity of quail of both of the photoperiodic regimes. Our findings indicate that not only osmotic stress but also photo-gonadal stimulation upregulates the expression of hypothalamic AVT genes and increases the localization of ir-AVT in many neurons of PVN. The above results support the existence of a parallel adrenal-gonad relationship and increase in adrenal function during osmotic stress, which also leads to simultaneous increase in AVT system. We conclude that photo-sexual conditions alter hypothalamic vasotocinergic and adrenal activity in Japanese quail and the degree of stimulation of the two systems following osmotic stress is higher under gonado-stimulatory LD conditions.     

Water flow and water storage in Agave deserti: osmotic implications of crassulacean acid metabolism

Abstract Water flow and water storage were investigated for Agave deserti, a desert succulent showing crassulacean acid metabolism (CAM). The anatomy and water relations of the peripheral chlorenchyma, where CAM occurs, and the central water-storage parenchyma were investigated for its massive leaves so that these tissues could be incorporated as discrete elements into an electrical-circuit analogue of the whole plant. The daily cycling of osmotic pressure was represented by voltage sources in series with the storage capacitors. With soil water potential and leaf transpiration rate as input variables, axial water flow through the vascular bundles and radial flows into and out of storage during the day/night cycle were determined. The predominantly nocturnal transpiration was coincident with increases in cell osmotic pressure and in titratable acid of the leaf chlorenchyma. In the outer layers of the chlorenchyma, water potential was most negative at the beginning of the night when transpiration was maximum, while the water-storage parenchyma reached its minimal water potential 9 h later. The roots plus stem contributed 7% and the leaves contributed 50% to the total water flow during maximal transpiration; peak water flow from the soil to the roots occurred at dawn and was only 58% of the maximal transpiration rate. Over each 24-h period, 39% of the water lost from the plant was derived from storage, with flow into storage occurring mainly during the daytime. Simulations showed that the acid accumulation rhythm of CAM had little impact on water uptake from the soil under the conditions employed. In the outer chlorenchyma, water potential and water flows were more sensitive to the day/night changes in transpiration than in osmotic pressure. Nevertheless, cell osmotic pressure had a large influence on turgor pressure in this tissue and determined the extent to which storage was recharged during the latter part of the night.     

Thirst and renal excretion of water and electrolytes during pyrogen fever in dogs.

Body temperature, water intake, urine output, sodium and potassium excretion, osmolal and free water clearance, plasma osmolality, sodium and potassium concentrations and osmotic thirst were examined in conscious dogs during pyrogen fever and compared to those found under control conditions. Arterial blood pressure and central venous pressure were also measured in some experiments. Administration of pyrogen produced transient but significant decreases in urine output and striking increases in the spontaneous water intake in some of the experiments in the phase of increasing fever. Arterial blood pressure decreased, whetreas central venous pressure increased at this stage of fever. No significant changes in renal excretion of solutes and free water as well as sodium and potassium were found. Plasma osmolality and sodium concentration increased and potassium concentration decreased unsignificantly both in control and pyrogen experiments. The main finding was that the thirst threshold to osmotic stimuli increased markedly during the phase of stabilized fever may be caused by significant increase in internal body temperature.