Hormonal growth-promotant effects on grain-fed cattle maintained under different environments

Six steers (3/4 Charolais×1/4 Brahman) (mean body weight 314±27 kg) and six spayed heifers (3/5 Shorthorn×2/5 Red Angus) (mean body weight 478±30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; °C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9±0.9°C ambient temperature (T_A) and 61.7±22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2±4°C (T_A) and 78.3±13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6±0.9°C (T_A) and 63.4±1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P<0.05) on cold days and greater (P<0.05) on hot days compared to TNL. On hot days, RTs, were 0.62°C higher after compared to before implanting. Across all conditions, RTs were >0.5°C greater (P<0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were >0.8°C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2–0.35°C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P<0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P<0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.     

Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Erinaceus europaeus

Summary Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (T _b ) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of T _b were collected. The hedgehogs were exposed to natural environmental conditions at 57°N in NE Scotland. Hedgehogs showed seasonal changes in mean daily euthermic T _b ,with a July maximum of 35.9±0.2°C, a September minimum of 34.7±0.9°C, and a marked circadian T _b cycle that correlates closely with photoperiod. Maximal T _b occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum T _b was most marked between April and September. The circadian T _b cycle was least correlated with photoperiod during winter. Hibernal T _b during winter correlated with ambient temperature (T _a ),it was maximal in September (17.7±1.0°C) and minimal in December (5.2±0.9°C). Apart from the tracking of T _a and T _b during hibernal bouts, with a time-lag of 4–6 h, circadian rhythmicity of hibernal T _b was not evident. However, the T _b of hibernating hedgehogs rose significantly when T _a fell below — 5°C, although the animals did not neccessarily arouse. Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45±5.1 h GMT while the mean time of the start of spontaneous arousal from hibernation was 11:53±4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night, when euthermic hedgehogs have maximalT _b ,or in deep hibernation around midday, when euthermic hedgehogs have minimal T _b .Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T _b falling to 25.8±3.1 °C. Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with T _a or body mass. TST bouts started at 06:51±4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear, but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4°C·h^-1, and when entering hibernation cooled at 7.9±1.9°C·h^-1. Warming rates were slightly higher during mid-winter when T _b and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31°N. These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.Abbreviations T _a ambient temperature - T _b body temperature - CSD circular standard deviation - SWS slow wave sleep - TST transient shallow torpor     

Pigeon flight in a wind tunnel

Summary Core temperatureT _c, breast temperatureT _s–br and leg temperatureT _s–1 were measured simultaneously in pigeons during rest and flight in a wind tunnel, using thermistors.MeanT _c at rest is 39.8±0.7°C and is independent of ambient temperatureT _a (10–30°C). In the first minutes of flight,T _c increases to 1.5–3.0°C above resting level and remains at this higher level. This hyperthermia increases withT _a (v=const.). It is±constant in the lowT _a range (10.6–13.9°C) at flight speeds v ranging from 10–18 m s^–1 and normal body mass, but increases with v and elevated body mass in the highT _a range (23.7–28.8°C). T _s–1 is adapted toT _a at rest and increases in flight up to 3–4°C belowT _c. This increase inT _s–1 is linear toT _a. T _s–br is always lower thanT _c, in extreme cases reaching restingT _c in flight.Supported by the Deutsche Forschungsgemeinschaft     

Cold tolerance in nematodes

Summary The nematodesTrichostrongylus colubriformis (J3),Ditylenchus dipsaci (J4) andPanagrellus silusae (adults) are freezing-susceptible but can avoid freezing by supercooling. Their mean supercooling points were –30.0±0.7°C forT. colubriformis, –21.7±0.7°C forD. dipsaci and –20.7±0.84°C forP. silusae. T. colubriformis andD. dipsaci could prevent seeding by external ice butP. silusae could not. The glycerol concentrations of these nematodes are considered to be too low to have a significant antifreeze effect.Abbreviations J3 3rd-stage juvenile - J4 4th stage juvenile - SEM standard error of the mean - T ₅₀ 50% survival temperature     

Effect of torpor on the water economy of an arid-zone marsupial,the stripe-faced dunnart (<Emphasis Type="Italic">Sminthopsis macroura</Emphasis>)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T_a) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 (T_a=30°C) to 3.13±0.22 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor at T_a=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing T_a, and ranged from 1.81±0.37 (T_a=30°C) to 5.26±0.86 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H₂O h^–1. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T_a investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.     

The Influence of Temperature on Metabolic and Cellular Protection of the Heart during Long-Term Ischemia: A Study Using P-31 Magnetic Resonance Spectroscopy and Biochemical Analyses

We have compared the influence of two different cold temperatures (below 10°C) for cardiac ischemia by measuring a large variety of hemodynamic and metabolic parameters during ischemia and reflow. Isolated isovolumic rat hearts were arrested with a preservation solution which was developed in our laboratory and then submitted to 5 h of cold storage (4°C, group I; and 7.5°C, group II) in the same solution. After an additional period of 50 min of ischemia at 15°C with intermittent cardioplegic infusion, hearts were reperfused for 60 min at 37°C. Function was assessed during the control period and reflow. High-energy phosphates and intracellular pH were followed by³¹P magnetic resonance spectroscopy. Analyses of metabolites and enzymes were performed by biochemical assays and HPLC in coronary effluents and in freeze-clamped hearts to assess cellular integrity. The energetic pool was better preserved at 4°C during ischemia (ATP at the end of 4°C ischemia, 59 ± 7% in group I vs 31 ± 5% in group II,P< 0.01) and reflow (P< 0.05) but membrane protection was higher when increasing the temperature to 7.5°C (reduction of creatine kinase leakage, 89 ± 16 IU/min in group I vs 51 ± 5 IU/min in group II,P< 0.05). As a result, functional recovery, represented by the rate pressure product, was higher in hearts preserved at 7.5°C (52 ± 6% recovery in group I vs 77 ± 7% in group II at the end of reflow,P< 0.05). Altogether, cold storage at 7.5°C provides a better protection than storage at 4°C.     

Ventilatory physiology of the numbat (<Emphasis Type="Italic">Myrmecobius fasciatus</Emphasis>)

This study examines the ventilatory physiology of the numbat (Myrmecobius fasciatus), a small to medium-sized (550 g) termitivorous marsupial. Ventilatory parameters at thermoneutrality reflect the slightly low (83% of predicted) basal metabolic rate of the numbat, with ventilation frequency (ƒ_R; 30.6±3.65 breaths min^–1), tidal volume [V_T; 6.0±0.66 ml at body temperature and pressure, saturated (BTPS)] and consequently minute volume (V_I; 117.7±15.22 ml min^–1; BTPS) all being 80–87% of that expected for a marsupial of similar body mass. Oxygen extraction was 27.7±1.37% in the thermoneutral zone. As is typical of marsupials, numbats accommodated increased oxygen consumption rates at ambient temperatures (T _a) below the thermoneutral zone by increasing minute volume (up to 411.2±43.98 ml min^–1; BTPS at T _a=10 °C) rather than oxygen extraction. Minute volume at 10 °C increased more by changes in ventilation frequency (up to 45.5±4.85 breaths min^–1) than tidal volume (9.4±1.03 ml, BTPS), as is also typical for a small-medium sized marsupial.Abbreviations BMR basal metabolic rate - BTPS body temperature and pressure, saturated - EO ₂ oxygen extraction - ƒ _R ventilation frequency - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - TNZ thermoneutral zone - V _I minute volume - V _T tidal volume - O ₂ oxygen consumption rate Communicated by I.D. Hume     

Seasonal and daily rhythms of body temperature in the European hamster (Cricetus cricetus) under semi-natural conditions

Body temperature of five European hamsters exposed to semi-natural environmental conditions at 47° N in Southern Germany was recorded over a 1.5-year period using intraperitoneal temperature-sensitive radio transmitters. The animals showed pronounced seasonal changes in body weight and reproductive status. Euthermic body temperature changed significantly throughout the year reaching its maximum of 37.9±0.2°C in April and its minimum of 36.1±0.4°C in December. Between November and March the hamsters showed regular bouts of hibernation and a few bouts of shallow torpor. During hibernation body temperature correlated with ambient temperature. Monthly means of body temperature during hibernation were highest in November (7.9±0.8°C) and March (8.2±0.5°C) and lowest in January (4.4±0.7°C). Using periodogram analysis methods, a clear diurnal rhythm of euthermic body temperature could be detected between March and August, whereas no such rhythm could be found during fall and winter. During hibernation bouts, no circadian rhythmicity was evident for body temperature apart from body temperature following ambient temperature with a time lag of 3–5 h. On average, hibernation bouts lasted 104.2±23.8 h with body temperature falling to 6.0±1.7°C. When entering hibernation the animals cooled at a rate of -0.8±0.2°C·h^-1; when arousing from hibernation they warmed at a rate of 9.9±2.4°C·h^-1. Warming rates were significantly lower in November and December than in January and February, and correlated with ambient temperature (r=-0.46, P<0.01) and hibernating body temperature (r=-0.47, P<0.01). Entry into hibrnation occured mostly in the middle of the night (mean time of day 0148 hours ±3.4 h), while spontaneous arousals were widely scattered across day and night. For all animals regression analysis revealed free-running circadian rhythms for the timing of arousal. These results suggest that entry into hibernation is either induced by environmental effects or by a circadian clock with a period of 24 h, whereas arousal from hibernation is controlled by an endogenous rhythm with a period different from 24 h.Abbreviations bw body weight - CET central European time - T _a ambient temperature - T _b body temperature - TTL transistor-transistor logic     

Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis)

Summary Behavioural activity, and core and surface temperatures of 4 unrestrained Galapagos fur seals were recorded in the natural habitat during their first weeks of life. Climatic variables were registered simultaneously. Pup behaviours were divided into bouts of resting (55% of total time), sucking (23%) and other activities (22%). Pups maintained a constant body temperature from their first day. Core temperature (T _e ) was 37.7° C±0.3° C (x ± SD) over 39 pup-days and 8 pup-nights. Skin temperature was correlated with T _c , but flipper temperature was not. No daily T _c rhythm was detected. Microclimate data were used to calculate operative temperature T _e . Environmental temperatures can be very high, with T _e above T _c 6–9 h a day for animals exposed to the sun, but below it in the shade. T _c is about 22° C at night. Pups avoid overheating mainly by withdrawing into the shade and reducing activity to a minimum during the hot hours of the day. Sun-exposed pups could be active at any time during the day if they had access to water, which was usually around high tide.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption     

Adaptive variations in heat production within Gerbils (genus Gerbillus) from different habitats

Summary Species of the genus Gerbillus are very common among the rodent fauna inhabiting arid zones and dune habitats in the palaearctic region. In Israel G. nanus is distributed in extreme arid areas, while G. allenbyi is common in coastal plain dune habitats, of mesic and semi-arid areas. Therefore, their distribution pattern is considered allopatric.Heat production, estimated by the oxygen consumption (Vo2), and body temperature (T _b) at various ambient temperatures were measured in both gerbils. The thermoneutral zone for G. allenbyi is between T _a=28–35° C ( T _b=36.3–38.3° C) and for G. nanus is at T _a=33±1° C ( , T _b=38.8° C). The values at thermoneutrality are 75.7% and 50.6% respectively of the calculated values for rodents with a mean body weight of 35.3 g and 28.4 g.Nonshivering thermogenesis (NST) was measured in both species as the maximal response to an injection of noradrenaline (2.0 mg/Kg s.c.). NST magnitude was the same for both species.The results show that both gerbils are adapted to arid environments. The difference in the thermoneutral zones of the two species is discussed in terms of its adaptive nature.     

Circular dichroism spectra of human hemoglobin reveal a reversible structural transition at body temperature

Previously we have shown that human red blood cells (RBCs) undergo a sudden change from blocking to passing through a 1.3±0.2-µm micropipette when applying an aspiration pressure of 2.3 kPa at a critical transition temperature (T_c=36.4±0.3 °C). Low-shear viscosity measurements suggested that changes in the molecular properties of hemoglobin might be responsible for this effect. To evaluate structural changes in hemoglobin at the critical temperature, we have used circular dichroism (CD) spectroscopy. The thermal denaturation curves of human hemoglobin A (HbA) and hemoglobin S (HbS) upon heating between 25 and 60 °C were non-linear and showed accelerated denaturation between 35 and 39 °C with a midpoint at 37.2±0.6 °C. The transition was reversible below 39 °C and independent of solution pH (pH 6.8–7.8). It was also independent of the oxygenation state of hemoglobin, since a sample that was extensively deoxygenated with N₂ showed a similar transition by CD. These findings suggest that a structural change in hemoglobin may enable the cellular passage phenomenon as well as the temperature-dependent decrease in viscosity of RBC solutions.     

Heat production in cold and long scotophase acclimated and winter acclimatized rodents

Heat production by means of oxygen consumptionVo₂ (at T_a = 6° C, 25° C, 30° C, and 32° C) and non-shivering thermogenesis (NST) were studied in individuals of a diurnal rodent (Rhabdomys pumilio) and a nocturnal rodent (Praomys natalensis). The studied mice were acclimated to cold at T_a=8°C with a photoperiod of LD 12:12. On the otherhand specimens of these two species were acclimated at T_a=25°C with a long scotophase LD8:16. The results were compared with a control group (T_a=25° C, LD 12:12) and winter acclimatized individuals of both species.Vo₂ in cold acclimated mice of both species was significantly increased when compared to the control group and was even higher than the winter acclimatized group when measured below the lower critical temperature. Long scotophase acclimated mice of both species also increased their oxygen consumption significantly when compared to the control group. NST was significantly increased in long scotophase acclimated mice from both species when compared to the control group. The results of this study indicate that the effects of acclimation to long scotophase are similar to those of cold acclimation. As changes in photoperiod are regular, it may be assumed that heat production mechanisms in acclimatization to winter will respond to changes in photoperiodicity.Present address: University of Haifa, Oranim, P.O. Kiryat Tivon, Israel.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

The degree of dietary fatty acid unsaturation affects torpor patterns and lipid composition of a hibernator

Diets rich in unsaturated and polyunsaturated fatty acids have a positive effect on mammalian torpor, whereas diets rich in saturated fatty acids have a negative effect. To determine whether the number of double bonds in dietary fatty acids are responsible for these alterations in torpor patterns, we investigated the effect of adding to the normal diet 5% pure fatty acids of identical chain length (C18) but a different number of double bonds (0, 1, or 2) on the pattern of hibernation of the yellow-pine chipmunk, Eutamias amoenus. The response of torpor bouts to a lowering of air temperature and the mean duration of torpor bouts at an air temperature of 0.5°C (stearic acid C18:0, 4.5±0.8 days, oleic acid C18:1, 8.6±0.5 days; linoleic acid C18:2, 8.5±0.7 days) differed among animals that were maintained on the three experimental diets. The mean minimum body temperatures (C18:0, +2.3±0.3°C; C18:1, +0.3±0.2°C; C18:2,-0.2±0.2°C), which torpid individuals defended by an increase in metabolic rate, and the metabolic rate of torpid animals also differed among diet groups. Moreover, diet-induced differences were observed in the composition of total lipid fatty acids from depot fat and the phospholipid fatty acids of cardiac mitochondria. For depot fat 7 of 13 and for heart mitochondria 7 of 14 of the identified fatty acids differed significantly among the three diet groups. Significant differences among diet groups were also observed for the sum of saturated, unsaturated and polyunsaturated fatty acids. These diet-induced alterations of body fatty acids were correlated with some of the diet-induced differences in variables of torpor. The results suggest that the degree of unsaturation of dietary fatty acids influences the composition of tissues and membranes which in turn may influence torpor patterns and thus survival of hibernation.Abbreviations bm body mass - T _a air temperature - T _b body temperature - FA fatty acid - MR metabolic rate - MUFA monounsaturated fatty acids - PUFA polyunsaturated fatty acids - VO₂ rate of oxygen consumption - SFA saturated fatty acids - UFA unsaturated fatty acids - UI unsaturation index - SNK Student-Newman-Keuls test     

Water permeability properties of the ovarian oocytes from Bufo arenarum and Xenopus laevis: A comparative study

The water permeability properties of ovarian oocytes from Xenopus laevis and Bufo arenarum, a toad species found in the Buenos Aires region, were studied. We report that: (i) the water osmotic permeability (P _f, cm/sec × 10^–4) was significantly higher in Bufo (6°C=12.3±2.4; 18°C = 20.8±4.8) than in Xenopus oocytes (6°C=5.3±0.3; 18°C=6.2±1.6). The corresponding water diffusion permeability values (P _d, cm/sec × 10^–4) were: Xenopus = 2.3±0.3 (6°C) and 4.8±0.7 (18°C); Bufo=2.7±0.4 (6°C) and 6.0 ±0.5 (18°C). (ii) Amphotericin B increased the P _f and P _d values. The observed P _fP _d ratio was not significantly different from the expected results (n=3), after amphotericin B incorporation in both species. This means that the influence of unstirred layers and other potential artifactual compounds did not significantly affect our experimental results, (iii) Preincubation with gramicidin during 12 hr induced a clear increase in the oocyte volume. After that, a hypotonic shock only slightly increased the oocyte volume. Conversely, a hypertonic challenge induced a volume change significantly higher than the one observed in control conditions, (iv) Mercury ions did not affect the osmotic permeability in Xenopus oocytes but clearly inhibited, in a reversible way, the osmotic permeability in oocytes from B. arenarum. (v) Mercury ions did not reduce P _d values in either species, (vi) The P _fP _d values calculated from the differences observed in these parameters between both species were 11.9±5.1 at 18°C and 15.5±2.4 at 6°C. These numbers are similar to those previously reported in the case of membranes having water channels. From these results, we propose that water channels are present in the ovarian oocyte from B. arenarum but not in the ovarian oocyte from X. laevis.This work was supported by Fundación Antorchas, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina) and Universidad de Buenos Aires (UBA). It was developed in the frame of an INSERM (France)-CONICET cooperative program.     

Comparative study on the thermostability of collagen I of skin and bone: Influence of posttranslational hydroxylation of prolyl and lysyl residues

Pepsin-solubilized collagen I from skin and bone was analyzed with regard to its thermal stability as a triple helical molecule in solution and afterin vitro fibril formation. Collagen I from human control bone was compared with samples showing deficiencies or surplus in the degree of hydroxylation of lysine. The helix to coil transitions were studied by circulardichroism measurements and limited trypsin digestion. Melting of fibrils from standardizedin vitro self-assembly was investigated turbidimetrically. Human control bone collagen I has a maximum transition rate (T _m ) at 43.3°C in 0.05% acetic acid. This is 1.9°C above control skin (T _m =41.4°C), most likely, due to a higher degree of prolyl hydroxylation—0.48 in bone vs. 0.41 in skin collagen I. Lysyl overhydroxylation of human and mouse bone collagen I appears to reduce theT _m slightly (1°C). Underhydroxylated bone collagen has aT _m which is 2°C below control. Melting temperatures ofin vitro formed fibrils are an indication for higher thermostability in parallel with an increase of lysyl hydroxylation. Accordingly, the melting temperature of such fibrils from human control skin, 49.3°C, exceeds control bone by 1.4°C. The degree of lysyl hydroxylation in these samples is 0.14 and 0.10, respectively. Further underhydroxylation (0.06) reduced it down to 45.4°C, while extensive overhydroxylation did not continue to increase the thermal stability of fibrils.     

Low-temperature limitations of photosynthesis in three tropical Vigna species: A chlorophyll fluorescence study

The temperature-dependence of photosynthesis and chlorophyll (Chl) fluorescence quenching components was studied between 0 and 45°C in three tropical, chilling-sensitive Vigna species and in chilling-tolerant pea. Photosynthesis of the Vigna spp. was approx. 20% more reduced by temperatures between 7 and 30°C than in pea. The latter revealed significant changes in Chl fluorescence parameters at much lower temperature than the Vigna spp. Below 15°C, the reduction state of Q_A increased quickly in pea, while in Vigna already below 30°C, an increase of reduced Q_A was obtained. The analysis of different components of non-photochemical Chl fluorescence quenching (q_N) revealed, that in pea photoinhibitory quenching (q_I) occurred below 13°C. Below ca. 7°C, a sudden breakdown of both q_P and the fast relaxing component of q_N was observed in pea.In Vigna, susceptibility of LHC II phosphorylation or limitation of electron flow by damage to PS I, the PS II reaction centre or the water-splitting system were not responsible for the chilling-sensitivity of photosynthesis between 5 and 30°C. Instead, photosynthesis was gradually limited by an inefficient use of reduction equivalents. This, in turn may increase susceptibilty to photoinhibition, which occurred below 20°C in Vigna. The combined study of q_P and of the different components of q_N allowed the demonstration of the subsequent occurrence of different limiting processes with decreasing temperature in the chilling-sensitive Vigna species.     

Determination of reduction potential of an engineered Cu<Subscript>A</Subscript> azurin by cyclic voltammetry and spectrochemical titrations

The reduction potentials of an engineered Cu_A azurin in its native and thermally denatured states have been determined using cyclic voltammetry and spectrochemical titrations. Using a 4,4-dipyridyl disulfide modified gold electrode, the reduction potentials of native and thermally denatured Cu_A azurin are the same within the experimental error (422±5 and 425±5 mV vs. NHE, respectively, in 50 mM ammonium acetate buffer, pH 5.1, 300 mM NaCl, 25 °C), indicating that the potential is that of a nonnative state. In contrast, using a didodecyldimethylammonium bromide (DDAB) film-pyrolytic graphite edge (PGE) electrode, the reduction potentials of native and thermally denatured Cu_A azurin have been determined to be 271±7 mV (50 mM ammonium acetate buffer, pH 5.1, 4 °C) and 420±1 mV (50 mM ammonium acetate buffer, pH 5.1, 25 °C), respectively. Spectroscopic redox titration using [Ru(NH₃)₅Py]²⁺ resulted in a reduction potential (254±4 mV) (50 mM ammonium acetate buffer, pH 5.1, 4 °C) similar to the value obtained using the DDAB film-PGE electrochemical method. Complete reoxidation of [Ru(NH₃)₅Py]²⁺-reduced Cu_A azurin is also consistent with the conclusion that this spectrochemical titration method using [Ru(NH₃)₅Py]²⁺ measures the reduction potential of native Cu_A azurin.Abbreviations CcO cytochrome c oxidase - N₂OR nitrous oxide reductase - ET electron transfer - CV cyclic voltammetry - NHE normal hydrogen electrode - DDAB didodecyldimethylammonium bromide - PGE pyrolytic graphite edge