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At least 343 records · Page 19Linked to original sources
PubMed1976

Role of sodium and urea in the renal concentrating mechanism in Psammomys obesus.

Micropunctures were performed at the tip of Henle's loops and vasa recta accessible at the extrarenal surface of the papilla in a desert rodent (Psammomys obesus) studied under mild NaCl ((NaCl 4%, 0.0375 ml/min) and mild urea (urea 4%, 0.0375 ml/min) loading conditions. In Nacl loaded animals, it was confirmed that solute addition (mainly sodium) contributes in a large proportion to the concentrating process along the thin descending limb. Comparison of sodium and urea concentrations in the loops with those in vasa recta at the same level of the papilla demonstrated that 1. the transepithelial sodium gradient was compatible with a diffusion transport of this ion from the interstitium to the thin descending limb; 2. the sodium concentration higher in interstitium than in the loop fluid was not compatible with the existence of a purely passive concentrating process in inner medulla as was recently proposed [8], 3. the transepithelial urea gradient was very limited which indicates that this solute does not play an important part in the concentrating process. In urea loaded psammomys, solute addition (mainly urea) to the thin descending limb fluid was still present but water abstraction was enhanced as compared to salt loaded animals, probably on account to the higher interstitial urea concentration. It is, thus, brought to evidence that the relative contribution of water abstraction and solute addition to the concentrating process along the thin descending limb can vary in a given species as a function of the physiological state.

Animals↗
PubMed1977

Physiological responses of dogs on exposure to hot, arid conditions. Serum constituents.

Serum electrolytes, metabolites and enzymes were determined in arterial blood of chronically cannulated dogs at room temperature and on exposure to 44-50 degrees C. These dogs were naturally acclimated to hot, arid conditions. In dogs maintaining their rectal temperatures (TR) below 40 degrees C, no significant changes were seen in the levels of Na+, Cl-, cholesterol, uric acid, alkaline phosphatase, lactic dehydrogenase or glutamic-pyruvic transaminase (SGPT). K+, CO2, glucose decreased significantly, and urea nitrogen (BUN) and glutamic-oxaloacetic transaminase (SGOT) showed small but significant increases. In several cases of excitable dogs, in which TR increased above 40 degrees C, we found large, significant increases in uric acid, SGPT and SGOT, and a decrease in cholesterol. The results suggest that in dogs maintaining their TR when exposed to high temperatures, changes in serum constituents indicate merely the presence of respiratory alkalosis and an increased energetic demand. When control of TR is lost, changes occur which suggest liver, and possibly cardiac, tissue damage.

Acclimatization↗
PubMed1981

Renal function and concentrating ability in a desert rodent: the gundi (Ctenodactylus vali).

Clearance and cortical micropuncture experiments were carried out on non diuretic gundis. In this species, the kidney has a long and well developed papilla but, unlike other desert rodents, the vascular organization of the outer medulla is very simple. After withdrawal of water supply for either 24 h or 3 days before the experiments, the urine osmolality was only 1,361 +/- 57, n = 9, before and 1,136 +/- 89 mosmol . kg-1 during anesthesia. The GFR per 100 g B.W.(0.450 ml . min-1) is lower than in the rat studied under similar conditions. With regard to electrolytes the tubular handling of Na, Ca, K and Mg is similar to that observed for another desert rodent, psammomys obesus. For P, massive reabsorption (more than 30% of the filtered load) takes place along the distal convoluted tubule. The relatively poor concentrating ability of the gundi's kidney is not due to a lack of medullary recycling of urea since a net addition of urea to short loops of Henle is observed in this species. Physiological and morphological observations concerning the gundi and other desert rodent species suggest that the vascular bundle development in the outer medulla might affect the renal response to water deprivation.

Animals↗
PubMed1988

Improved thermoregulation caused by forced water intake in human desert dwellers.

Residents of the Negev desert in Israel sustain a mild state of dehydration. Low, concentrated urine outputs, high incidence of kidney diseases and high hematocrit ratios characterize this population. Educational programs to increase the awareness of the population to the dangers of dehydration have undoubtedly failed. It was our purpose to see whether forced increased drinking will affect the above variables. Ten healthy subjects were asked to double their normal voluntary water intake without (phase II) and with salt supplements (50 mM NaCl, 20 mM KCl) (phase III), for one week. After phases II and III significant increases in body masses, decreased concentrations of serum proteins, hemoglobin, hematocrit ratios and serum osmolalities were found. No significant changes were found in the concentrations of sodium and potassium in the serum. At the end of each phase, the subjects were asked to exercise on a bicycle ergometer for 60 min at 50% VO2max in a heated chamber at 45 degrees C, and 30%-50% relative humidity. Experiments were terminated if and when heart-rates exceeded 180 bpm or the rectal temperature increased to 39 degrees C. After both experimental phases, subjects increased their tolerance to heat, extending the exercise periods by 25% and 30%. Compared with their starting levels, hematocrit ratios, serum proteins and hemoglobin concentrations increased in phases II and III while no changes were recorded in the control period (phase I). It is suggested that spontaneous voluntary water drinking in desert dwellers is not enough to achieve a true state of "euhydration".

Adult↗
PubMed1985

Identification of crystalline allantoin in the urine of African Cricetidae (Rodentia) and its role in their water economy.

All eleven cricetid species, examined in this investigation, produced an off-white crystalline precipitate in their urine when deprived of water, whereas not one murid examined did so. This crystalline compound was identified as allantoin, a common end product of purine catabolism. The quantity found in the solid precipitate alone accounted for 47% of the total nitrogen excreted and was approximately 14 times greater than the predicted quantity of allantoin from purine degradation. It appears that there is a shift in nitrogen excretion from urea to allantoin in the Cricetidae. Water-deprived cricetids had higher urine osmolalities, urea concentrations and lower daily percentage body water turnovers than the murids. This can be explained by the substantial water savings associated with excreting solid allantoin. The discrepancy in the mode of nitrogen excretion between the two families inhabiting the Namib Desert can be attributed to their different evolutionary histories, the Cricetidae being pre-adapted for survival in deserts.

Adaptation, Physiological↗
PubMed1987

Renal excretion capacity in hydrated desert rodents (Jaculus orientalis and Jaculus deserti).

The capacity to excrete a water load was studied in rats and in two desert rodents (Jaculus orientalis and Jaculus deserti) adapted to either 5 or 30 degrees C ambient temperature. The rat is able to eliminate the entire water load regardless of thermal adaptation. Cold-adapted J. orientalis and J. deserti excreted 60% of the water load in comparison to 20-30% in warm-adapted jerboas. At both adaptation temperatures, antidiuretic hormone (ADH) concentration was estimated at maximum diuresis in the two desert species. Though hydration induced a significant decrease in ADH concentration in both species, its level in the plasma remained relatively high. The decrease was more pronounced in J. orientalis than J. deserti.

Acclimatization↗
PubMed1979

Soil stabilization by a prokaryotic desert crust: implications for Precambrian land biota.

A cyanophyte dominated mat, desert crust, forms the ground cover in areas measuring hundreds of square meters in Utah and smaller patches in Colorado. The algal mat shows stromatolitic features such as sediment trapping and accretion, a convoluted surface, and polygonal cracking. Sand and clay particles are immobilized by a dense network of filaments of the two dominating cyanophyte species, Microcoleus vaginatus and M. chthonoplastes, which secrete sheaths to which particles adhere. These microorganisms can tolerate long periods of desiccation and are capable of instant reactivation and migration following wetting. Migration occurs in two events: 1. immediately following wetting of dry mat, trichomes are mechanically expelled from the sheath as it swells during rehydration, and 2. subsequently, trichomes begin a self-propelled gliding motility which is accompanied by further production of sheath. The maximum distance traveled on solid agar by trichomes of Microcoleus vaginatus during a 12 hour period of light was 4.8 cm. This corresponds to approximately 500 times the length of the fastest trichome, and provides a measure of the potential for spreading of the mat in nature via the motility of the trichomes. Dehydration resistence of the sheath modifies the extracellular environment of the trichomes and enables their transition to dormancy. Following prolonged wetting and evaporative drying of the mat in the laboratory, a smooth wafer-like crust is formed by the sheaths of Microcleus trichomes that have migrated to the surface. Calcium carbonate precipitates among the algal filaments under experimental conditions, indicating a potential for mat lithification and fossilization in the form of a caliche crust. It is suggested that limestones containing tubular microfossils may, in part, be of such an origin. The formation of mature Precambrian soils may be attributable to soil accretion, stabilization, and biogenic modification by blue-green algal land mats similar to desert crust.

Cyanobacteria↗
PubMed1980

Endolithic microbial life in hot and cold deserts.

Endolithic microorganisms (those living inside rocks) occur in hot and cold deserts and exist under extreme environmental conditions. These conditions are discussed on a comparative basis. Quantitative estimates of biomass are comparable in hot and cold deserts. Despite the obvious differences between the hot and cold desert environment, survival strategies show some commom features. These endolithic organisms are able to 'switch' rapidly their metabolic activities on and off in response to changes in the environment. Conditions in hot deserts impose a more severe environmental stress on the organisms than in the cold. Antarctic desert. This is reflected in the composition of the microbial flora which in hot desert rocks consist entirely of prokaryotic microorganisms, while under cold desert conditions eukaryotes predominate.

Cell Survival↗
PubMed1992

Summer-arrested development of abomasal trichostrongylids in Awassi sheep in semi-arid areas of north-west Syria.

Inhibition in trichostrongylids was studied in Awassi sheep in North-west Syria, which has cold winters and hot summers. On six occasions during a 1-year period, five ewes with natural helminth infections were slaughtered after being held in pens for 3 weeks. The percentage of inhibited larvae was lowest in January (6%); it increased during the spring to 76.7% in April and to 84.6% in June and then decreased during the autumn (57.1% in September, 26.1% in December). Inhibition occurred mainly during the early fourth stage in mucosa but was also observed during the late fourth stage in digesta. Teladorsagia circumcincta was the main species involved, but it seemed that this phenomenon also occurred in Marshallagia marshalli.

Abomasum↗
PubMed1991

Biometeorology and animal protein production: the case of arid lands.

To meet the food demands of the ever-increasing world population, man's only major future land bank is the arid lands. However, their exploitation has been limited and constitutes a major challenge to many scientific disciplines. Under the present conditions of hunger and/or malnutrition, a large-scale expansion in food production is not to be expected. Hence, it is imperative that in any development programme for arid lands, malnutrition, in general, and a deficiency of animal proteins, in particular, should be considered. Major advancements have been made, but much remains to be learned and implemented. Improvement of native farm animals should be the first step in increasing the availability of animal proteins. This may be achieved by an educational programme to enhance management, housing, food intake, etc. Then a breeding programme selecting for high productivity can be pursued. After eliciting the maximum return from the present livestock, attention should be directed to domesticating wild ungulates and/or introducing highly productive temperature-zone breeds for upgrading the local animals. Additionally, new potential and unconventional sources of animal proteins must be explored. Aquaculture, in particular, has the potential of producing large quantities of lower-cost protein-rich food. Available evidence in arid regions of the developed countries, i.e. USA and Australia, promises favourable results in our efforts toward increasing the production of animal protein. By innovative methods and long-term planning, such successes can be adapted and transferred to other regions of the world, with the aim of gradually lessening the present state of malnutrition and hunger.

Animal Husbandry↗
PubMed1995

Acetylcholinesterase from desert cobra (Walterinnesia aegyptia) venom: optimization and kinetics study.

Acetylcholinesterase (AChE) was investigated in Walterinnesia aegyptia venom and characterized with respect to its kinetic properties. It was found that 4.0 micrograms of crude venom protein and an incubation time of 4.0 min were suitable conditions for linearity of AChE activity at 25 degrees C. The optimum strength of the sodium phosphate buffer was 0.05 M, and the optimum pH was 7.75. The optimum temperature was 30 degrees C. The activation energy and the heat of activation were observed to be 6510 and 5922 cal/mole. The AChE was specific for acetylthiocholine but it did not hydrolyse butyrylthiocholine. The optimum substrate concentration was 3.0 mM but at higher substrate concentrations, the AChE activity declined. The ASCh concentration ranges for different orders of the reactions were determined and kinetic parameters (Km, Vmax, Kcat, and Ksp) were established at each order of the reaction.

Acetylcholinesterase↗
PubMed1991

The influence of climatic conditions on the heat balance of the human body.

The structure of heat exchange between the human body and its surroundings has been studied according to M.I. Budyko's model. Comparative measurements were carried out in the Polish Lakeland (maritime, temperate warm climate), in Central Mongolia (continental, temperate cool climate), and in the Kara Kum desert (dry subtropical climate). The results deal with the summer and early autumn seasons. The calculations indicate that the quantitative apportionment of various forms of heat exchange depend on specific weather conditions, which are typical for the distinguished climatic zones.

Body Temperature Regulation↗