I. Choshniak

THE EFFECT OF SALINITY ON GROWTH RATE, SURVIVAL AND SWIMBLADDER INFLATION IN GILTHEAD SEABREAM, SPARUS AURATA, LARVAE

Abstract The effects of salinity (15–40 p.p.t. salinity; 450–1200 mOsm kg−1) on growth, survival and swim bladder (SB) inflation in gilthead seabream, Sparus aurata, were evaluated. Over the salinity range tested, 1–32 day old seabream larvae were found to be osmotic regulators. Within the range tested, 1 day old larvae maintained an osmotic pressure of 224 mOsm kg−1, significantly lower than 410 mOsm kg−1 in 13 and 24 day old larvae. In addition, water content in larvae was negatively correlated with age, being over 86% in 4 day old larvae and 83% in 32 day old larvae. A negative relationship was found between salinity and survival; as the rearing salinity decreased from 40 to 25 p.p.t., survival increased from 5.3 to 18.6%. Larval final dry weight (DW) and wet weight (WW) were over 16% higher at 25 than 40 p.p.t. salinity. Finally, reduced salinity induced a significant increase in the rate of SB inflation; 65 to 92.5% in 40 and 25 p.p.t. acclimated larvae, respectively.

Daily Rhythms of Metabolic Rate and Body Temperature of Two Murids from Extremely Different Habitats

Daily circadian rhythms of body temperature (Tb) and oxygen consumption (VO2) were measured in two murid species, which occupy extremely different habitats in Israel. The golden spiny mouse (Acomys russatus) is a diurnal murid distributed in arid and hot parts of the great Syrio-African Rift Valley, while the broad-toothed field mouse (Apodemus mystacinus) is a nocturnal species that inhabits the Mediterranean woodlands. In both species, the daily rhythms of Tb and VO2 are entrained by the photoperiod. Under laboratory experimental conditions (ambient temperature Ta = 33 degrees C and photoperiod regime of 12L:12D), Acomys russatus exhibits a tendency towards a nocturnal activity pattern, compared to the diurnal activity displayed by this species under natural conditions. Under the same photoperiod regime and at Ta = 28 degrees C, Apodemus mystacinus displays nocturnal activity, as observed under natural conditions. The maximal values of Tb were recorded in Acomys russatus at midnight (23:50 h), while the maximal values of VO2 were recorded at the beginning of the dark period (18:20 h). In Apodemus mystacinus, the maximal values of Tb and VO2 were recorded at 23:40 and 20:00 h, respectively. The ecophysiological significance of these results is discussed further.

Homeostatic responses to water deprivation or hemorrhage in lactating and non-lactating bedouin goats

Three lactating and three non-lactating black Bedouin goats were subjected to four days of water deprivation or to hemorrhage. Four days of water deprivation caused body wt losses of 32 and 23% and plasma volume losses of 30 and 34% in lactating and non-lactating goats respectively. Plasma osmolality increased 17 and 15% in lactating and non-lactating goats. Plasma arginine vasopressin concentration rose from about 5 pg/ml to a mean of 36 pg/ml. Plasma renin activity increased from about 0.7 ng/ml/hr to a mean of 3.45 ng/ml/hr in lactating and to 3.15 ng/ml/hr in non-lactating goats. At 4.5 hr post-rehydration plasma osmolality and plasma vasopressin concentration were back to normal in non-lactating, but still elevated in lactating goats. Plasma renin activity increased after rehydration. Rapid blood volume loss of 21-28% increased plasma vasopressin concentration to 16-35 pg/ml in non-lactating and to 70 or greater than 500 pg/ml in lactating goats. It is concluded that black Bedouin goats are well adapted to endure severe dehydration and rapid rehydration, but that they (especially lactating animals) react strongly to rapid volume depletion.

Effects of dehydration and rehydration on body temperatures in the black Bedouin goat

Abstract The temperatures of the arterial blood and the brain in black Bedouin goats were measured continuously by miniature data loggers. The animals were either euhydrated or dehydrated to 75–80% of the initial body mass by withholding water for 3–4 days during exposure to intense solar radiation. The daily blood temperature means and maxima of were significantly higher in dehydration than in euhydration, but 40°C was rarely exceeded even during the hot hours of the day. Selective brain cooling occurred in euhydration, but its extent was small when blood temperature was below 39.5°C. In dehydration, however, selective brain cooling was frequent and the standard response when blood temperature exceeded 39°C. We believe that selective brain cooling contributes to the inhibition of evaporative heat loss, which is the primary cause of the higher blood temperature in dehydration. Rapid rehydration with cold water induced long-lasting depression of blood temperature. No evidence was found for mechanisms attenuating the subsequent decrease of brain temperature which occurred a few minutes after the uptake of cold water.

Myocardial regional blood flow: Quantitative measurement by computer analysis of contrast enhanced echocardiographic images

Quantitation of regional myocardial blood flow constitutes the missing link between the anatomy of coronary obstruction and its physiological effect on regional oxygen supply. Microscopic air bubbles, introduced into the coronary circulation, were shown to produce a transitory enhancement of the myocardial tissue contrast, easily detectable with standard ultrasonic imaging equipment. This study presents a new approach linking the tissue blood flow with the time-dependent changes in the intensity of the ultrasonic reflections produced by the microbubbles. The tissue blood flow is evaluated using the well-known indicator dilution relation, according to which flow equals the ratio between the intravascular fraction of the tissue sample volume and the mean transit time of the contrast agent. We derive these two parameters from the time curves representing the contrast induced variations in the mean videointensity measured in two regions of interest, a reference region in the left ventricular cavity and the region of interest within the myocardial tissue. The intravascular volume fraction is computed as the ratio of the total power of the above two intensity curves, as each of these is assumed to be proportional to the total amount of tracer traversing the corresponding region of interest. The mean transit time is computed using combined time- and frequency-domain processing, involving Fourier deconvolution of the response function of the myocardial tissue sample. This approach was validated in an in vivo model in a series of animal experiments involving left atrial injection of albumin coated air microbubbles (Albunex). Videointensity curves obtained during contrast enhancement of the myocardium were analyzed to provide values of regional myocardial blood flow (in mL/min/100 g) in 45 myocardial regions of interest defined in 7 experiments performed on 4 animals. The values obtained with our approach correlated well (r = 0.77, p < 0.001) with standard reference measurements based on radiolabeled microspheres. The intertechnique variability was found to be smaller than the intersegment variability characterizing our technique. The difference between the mean flow values obtained with microspheres for segments of the entire heart and the mean flow obtained with our technique for all regions of interest ranged between 1 to 19% in the 7 experiments. In its present form, based on left atrial or left ventricular injection of contrast solution, this method may allow, for the first time, quantitative evaluation of myocardial regional blood supply in the cardiac catheterization laboratory or the operation theater.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid Rehydration and Kidney Function in the Black Bedouin Goat

Black goats, tended by Bedouin tribesmen in the extreme deserts of the Middle East, drink only once every 2-4 days and imbibe amounts of water that often exceed 40% of their dehydrated body weight. The water that the goats drink copiously is first retained in the rumen and only gradually flows into the other body fluid compartments. Five hours after the drinking, 81% of the water imbibed was still stored in the spacious rumen of the goat. The kidney of the Bedouin goat responded to the voluminous drinking by a drop in the blood flow that was followed by a compatible drop in both the GFR and the urine flow. The urine flow, even 4 h following the drinking, was below the rate recorded in the dehydrated animal. Urine Na⁺ concentration that amounted to 80.3 mM in the dehydrated animal dropped to only 37.7 mM following the drinking. A drop (from 144 mM to 49 mM) was also simultaneously recorded in Cl⁻ concentration; K⁺ and urea concentration, however, changed only slightly. It is suggested that the rumen in the goat serves as a water reservoir that helps maintain the osmotic stability of the body proper. The kidneys in these animals efficiently conserve the water imbibed as well as the bodys Na⁺ and Cl⁻. Studies of sheep that assign similar roles to the rumen and the kidneys indicate that the physiological mechanism described in the present study is generally shared by ruminants tended in a pastoral system.

Effects of infrequent drinking on the nitrogen metabolism of Bedouin goats maintained on different diets

The effect of infrequent drinking on nitrogen metabolism was studied in Bedouin goats, a breed herded in the extreme deserts of the Middle East. The goats were given water either daily or only once every 4 days, while being maintained on roughages of different quality: lucerne hay (19% protein), Rhodes grass (10% protein) or wheat straw (3·7%). On lucerne hay and Rhodes grass the goats kept their body mass constant, whether given water daily or only once every 4 days. When on wheat straw the body mass was maintained constant only when given water once every 4 days. Infrequent drinking was found to hamper considerably the food intake of the goats when fed on high quality roughage. When on the wheat straw, the nitrogen intake of the goats (only 12% of that recorded when fed lucerne hay and given water daily) was, however, not affected by the drinking regime. Infrequent drinking improved nitrogen digestibility on all the diets, but more so on those of low quality than on the lucerne hay. When tested on the low quality feeds, urea excretion was low and urea retention and recycling were maintained at high rates. Infrequent drinking had no adverse effect on these capacities.

Effect of dehydration and rapid rehydration on renal function and on plasma renin and aldosterone levels in the black Bedouin goat

Bedouin goats in the extreme deserts of the Middle East are regularly subjected to severe dehydration and possess a capacity to rapidly rehydrate by drinking large volumes of water. Urine flow, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in the fully hydrated animals amounted to 0.74±0.4 ml · min−1, 76±29 ml · min−1 and 344±146 ml · min−1 respectively. In goats that were dehydrated to a loss of about 30% of their initial body weight, urine flow dropped to 24% of the value recorded in the hydrated animals and GFR and ERPF dropped to half their level recorded in the hydrated phase. Na and K+ excretion decreased in the water depleted goats and further decrease was recorded following drinking. Following drinking the urine flow, GFR and ERPF of the recently rehydrated goats dropped to below the rates recorded in the dehydrated animals. During the 3 h of the continuous recording that followed the drinking, all three rates did not exceed the predrinking level. Plasma renin activity amounted to 0.37±0.32 ng AI·ml−1·h−1 in the hydrated animals. In dehydrated ones it amounted to 4.8±2.8 ng AI·ml−1·h−1 and a further increase was recorded following drinking. Aldosterone in the hydrated goats was 5.5±4.3 ng% and increased to 13.9±2.3 ng% in the dehydrated animal and amounted to 20.1±5.5 ng% 2 h following drinking. It is concluded that the kidney in the Bedouin goat plays a major role in conserving both water and solutes, not only when deprived of water but also following its rapid rehydration.

Rapid rehydration in the black bedouin goats: Red blood cells fragility and role of the rumen

Abstract 1. 1. Following dehydration, Bedouin goats regularly drink volumes of water amounting to 30–40% of their bodyweight. 2. 2. In vitro experiments showed that 50% hemolysis of the red blood cells of these goats occurred at a concentration of 110 mM NaCl. 3. 3. Blood plasma concentration dropped from 336.5± 6.9 mOsm/Kg before drinking, to only 303.7 ± 7.6, 6 hr afterwards. Changes in plasma volume were moderate too. 4. 4. The rumen was shown to first retain the water imbibed, and to release it only gradually later on: within 5 hr following the drinking only 18% of the ruminal fluid left the rumen.

Sweat Gland Secretion in the Black Bedouin Goat

The black bedouin goat is indigenous to the Negev Desert and the Sinai Peninsula and is unusual when compared with other breeds of goat in that it uses sweating rather than panting as its main mode of evaporative heat loss. The sweat rate from the side of the head is greater than that from the thorax. The rate of passive diffusion of water is similar to that of other mammalian species. There is no evidence that circulating adrenaline, either at rest or during exercise, stimulates sweat gland activity. The high rate of sweating is achieved mainly by the individual sweat glands, which secrete at a rate five to 10 times greater than other bovid species. It is concluded that the relatively high solar heat load imposed on this breed of goat by virtue of its black color is primarily dissipated by the development of sweat glands with a high secretory capacity.