Therapeutic Effect of Liposomal Superoxide Dismutase in an Animal Model of Retinopathy of Prematurity

A newborn rat model of retinopathy of prematurity was used to test the hypothesis that a lack of superoxide dismutase contributes to the retinal vaso-attenuation seen during exposure of the animals to hyperoxic conditions. To determine the endogenous superoxide dismutase activity of the retina under hyperoxic conditions, litters of albino rats were placed in either constant 80% ambient oxygen (constant hyperoxia), or placed in 21% oxygen (room air) immediately after birth. Every other day, for 14 days, several rat pups were sacrificed and their retinas removed for the determination of total superoxide dismutase (SOD) activity and manganese-associated SOD activity. An attempt was made to increase retinal SOD activity by intraperitoneal administration of exogenous SOD encapsulated in polyethylene glycol-modified liposomes. Additional litters were exposed to the same oxygen treatments and supplemented twice daily with either liposome-encapsulated superoxide dismutase in saline or liposomes containing saline without SOD. Animals were sacrificed at various time points for the determination of total superoxide dismutase activity and computer-assisted analysis of vessel density and avascular area. Animals raised in an atmosphere of constant 80% oxygen had significantly reduced levels of retinal superoxide dismutase activity through 6 days of life when compared to their room air-raised littermates. At 6 days of age, daily supplementation with liposome-encapsulated SOD had significantly increased retinal superoxide dismutase activity and reduced oxygen-induced vaso-attenuation as evidenced by increased vessel density and decreased avascular area, when compared to littermates exposed to constant hyperoxia that received control liposomes. Superoxide dismutase had no adverse effects on any of the animals regardless of treatment. Tracing experiments demonstrated that liposomes entered the retina and were found in cells morphologically resembling mi-croglia. Delivery of SOD to the retina via long-circulating liposomes proved beneficial, suggesting that restoration and/or supplementation of endogenous antioxidants in oxygen-damaged retinal tissue is a potentially valuable therapeutic strategy.     

Effect of thermoperiod on diapause intensity in Pyrrhocoris apterus (Heteroptera Pyrrhocoridae)

The intensity of adult diapause in Pyrrhocoris apterus was measured in two series of experiments as the duration of pre-oviposition period at a constant temperature of 25 degrees C after transfer from short (12L:12D) to long day conditions (18L:6D). Higher diapause intensity was induced with a thermoperiod than at constant temperatures. After the induction throughout larval instars 3-5 and during 4 weeks of adult life at short days and a thermoperiod of 25/15 degrees C the pre-oviposition period was 30+/-4 and 26+/-3 days. After induction at constant 25 degrees C the pre-oviposition period was 22+/-3 and 23+/-4 days, while after induction at constant 20 degrees C it was 17+/-4 and 19+/-4 days. Induction at a lower constant temperature of 20 degrees C was thus followed by a less intense diapause than the induction at a higher constant temperature of 25 degrees C. These counterintuitive results are discussed. The oxygen consumption rate measured at experimental temperatures prior to transfer from short to long days was higher at thermoperiodic conditions than at constant temperatures and it was similar at constant 20 and 25 degrees C. Thus, the oxygen consumption rate measured prior to the transfer was highest (indication of the least intense diapause) in the insects that showed later, after the transfer to long days, the longest pre-oviposition period (indication of the most intense diapause). Within the first two days after transfer to constant 25 degrees C, oxygen consumption rate measured at 25 degrees C decreased in the thermoperiodic insects, while it transiently increased in insects from constant 20 degrees C. Two days and later after the transfer, oxygen consumption rate was similar in all groups. Cold hardiness was not correlated with diapause intensity. The low lethal temperature in diapausing insects was correlated with the night temperature during diapause induction.     

IMPAIRMENT OF GROWTH AND DEVELOPMENT OF THE RAT BRAIN BY HYPEROXIA AT ATMOSPHERIC PRESSURE

Abstract— The continuous exposure of newborn rats to 70–80 per cent oxygen at atmospheric pressure throughout the iirst 9 days of life significantly inhibited the growth of the brain which normally occurs during this period of life. The accumulations of DNA, RNA, total protein, and proteolipid protein which accompany brain growth during this period were all approximately proportionately depressed by the oxygen-enriched atmosphere. RNA/DNA and protein/DNA ratios were unaffected. The increase in brain mass in the first week of life reflects mainly cell proliferation, and since the decreased DNA accumulation occurred with no changes in RNA/DNA and protein/DNA ratios, we conclude that the effect of oxygen was to inhibit cellular division. We estimate that the oxygen exposure caused an approximately 7 per cent deficit in the cell population of the brain. These results indicate that the use of elevated concentrations of oxygen may have serious deleterious effects on the growth and development of the brain.     

Development of temperature regulation in the common white-toothed shrew, Crocidura russula

1. Body temperature and oxygen consumption were measured during the first month of postnatal life in two litters of Crocidura russula at four different ambient temperatures. 2. Body temperature in the nest varies from 30.5-35.0 degrees C during the first 10 days; afterwards it becomes more constant (35.5-37.0 degrees C). 3. First homoiothermic reactions occur on the 2nd day of life and become effective on the 4th day. 4. In the case of undernourished shrews, torpor is already developed on the 2nd day. 5. After the 7th day torpor is the obligatory reaction in cooling experiments. 6. This discontinuous development of temperature regulation is interpreted as typical for shrews capable of torpor.     

Differential effects of prostaglandins and arachidonic acid on gastric circulation and oxygen consumption

Experiments were carried out on anesthetized dogs to compare the effects of prostaglandin E₂ (PGE₂), prostacyclin (PGI₂) and arachidonic acid (AA) administered intraarterially on gastric blood flow and oxygen consumption during constant arterial pressure perfusion and constant flow perfusion of the stomach. Both PGE₂ and PGI₂ increased total blood flow and oxygen consumption both in the resting stomach and following histamine stimulation although the effects of PGE₂ on the oxygen consumption in stimulated stomach were not statistically significant. On the contrary, AA decreased both gastric blood flow and oxygen consumption in the histamine stimulated stomach. To determine if these compounds can influence gastric oxygen consumption independently of their effects on blood flow, the experiments with constant flow perfusion were performed. Both PGE₂ and PGI₂ decreased both the perfusion pressure and oxygen consumption in the resting as well as in the histamine-stimulated stomach whereas AA increased perfusion pressure and decreased oxygen consumption during histamine administration. Effects of AA were blocked by indomethacin suggesting that not AA itself but some of its metabolites, most likely thromboxanes were responsible for the hemodynamic and metabolic changes resulting from the contraction of gastric arterioles and precapillary sphincters. On the contrary, both PGE₂ and PGI₂ caused gastric hyperemia and an increase in oxygen consumption in the resting stomach, but decreased the latter parameter in the stimulated stomach, most probably as a result of secretory inhibition overcoming direct vascular effects of these compounds.     

Oxygen and effective vasular compliance in acute heart failure.

The effect of hypoxemia on total vascular compliance was studied in anesthetized dogs using a venous bypass technique. Cardiac output was kept constant with an extracorporeal pump and respiration controlled to maintain normocapnia. When nitrogen was added to the respired gas to produce an arterial PO2 approximately 45 mm Hg, total vascular compliance was rapidly and significantly reduced to 0.93 ml (mm Hg)(-1) kg(-1) with incomplete recovery to baseline values of 1.30 plus or minus 0.06 ml (mm Hg)(-1) kg(-1) during subsequent ventilation with 100% oxygen. Acute heart failure was induced by gradual aortic constriction. Ventilation with 100% oxygen failed to prevent a gradual reduction in total vascular compliance to 0.86 ml (mm Hg)(-1) kg(-1) from a baseline value of 1.23 plus or minus 0.06 ml (mm Hg)(-1) kg(-1). Ventilation with 100% oxygen following the reduction in vascular compliance during acute heart failure also failed to significantly alter this parameter. Thus, improvement of arterial oxygen tension in patients with acute heart failure would be beneficial in providing greater oxygen delivery to the tissues without abolishing a compensatory mechanism of reduced vascular compliance which attempts to maintain a cardiac filling gradient of pressure.     

Changes in free fatty acids and diglycerides in mouse brain at birth and during anoxia

Abstract: Within the first few hours of life in the mouse, marked changes were seen in brain endogenous free fatty acids (FFA). A 21% decrease in the total FFA pool occurred during the 1st h of life, and a constant value was maintained thereafter to 10 h. Polyunsaturated fatty acids displayed a different pattern of change. There was 27% less free ararhidonic acid at birth (0 h) than 1 h later. Similar values were obtained for docosahexaenoic acid at birth and at 10 h, although palmitoleic and oleic acids decreased markedly after 1 h. The polyunsaturated fatty acyl chains of diglycerides (DG) showed a statistically significant increase as a function of time after birth, despite an unchanged total DG pool size. The brains of pups subjected to 40 min of N₂-anoxia immediately after delivery exhibited a decrease in FFA, especially the monoenoic components, but 60 min of anoxia yielded higher FFA levels. Anoxia induced at 10 h increased FFA and arachidonic acid was higher than when anoxia was induced at 0 h. FFA accumulation was further stimulated by raising the environmental temperature during anoxia. When anoxia was induced, DG exhibited a net increase in palmitate, oleate, and palmitoleate at 0 and 10 h. No arachidonoyl-DG accumulated at 0 h, even after 60 min of anoxia, and stearate was unchanged at 0 and 10 h. The lipid changes observed in the brain during the first hours of life suggest that the enzymatic reactions that promote accumulation of free arachidonic and docosahexaenoic acids and arachidonoyl-DG in the mature brain are present at low levels at the time of delivery. The sluggish modifications found in our study may be related to the longer resistance of newborns to oxygen deficiency.     

Effects of different ambient temperatures on physiological responses during exercise and recovery with special reference to energy requirement

Observation of the physiological responses was made on seven young male subjects ages 27–31, during pedalling a bicycle ergometer at the constant work load of 600 kg. m/min for 20 min and recovery in 35°C with 50% RH, in 30°C with 50% RH and in 23°C with 50% RH. Heart rate, respiratory volume, total oxygen intake and energy requirement were increased with an increase in ambient temperature, while blood pressures were lower in a hot environment than in cooler environments. In 35°C, oxygen intake during exercise, oxygen debt and anaerobic fraction of oxygen debt had increased when compared with those in 23°C. Thus it is inferred that the energy requirement, the oxygen debt and the anaerobic fraction of the oxygen debt for a fixed work had increased more in a hot environment than in a comfortable environment. Factors which caused differences in the physiological reactions during exercise and recovery in different conditions are discussed.     

Predicting the population dynamics of the house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) in response to a constant hygrothermal environment using a model of the mite life cycle

A generalised model of the life cycle of a house dust mite, which can be tailored to any particular species of domestic mite, is presented. The model takes into account the effects of hygrothermal conditions on each life cycle phase. It is used in a computer simulation program, called POPMITE, which, by incorporating a population age structure, is able to predict population dynamics. The POPMITE simulation is adapted to the Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) (DP) mite using published data on the egg development period, total development period, adult longevity, mortality during egg development, mortality during juvenile development, and fecundity of individual DP mites held at a range of constant hygrothermal conditions. An example is given which illustrates how the model functions under constant hygrothermal conditions. A preliminary validation of POPMITE is made by a comparison of the POPMITE predictions with published measurements of population growth of DP mites held at a range constant hygrothermal conditions for 21 days. The POPMITE simulation is used to provide predictions of population growth or decline for a wide range of constant relative humidity and temperature combinations for 30 and 60 days. The adaptation of the model to correctly take account of fluctuating hygrothermal conditions is discussed.     

The growth and energy metabolism of <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis> (Lymnaeidae,Gastropoda): I. Early postlarval period

The growth and the oxygen consumption rate of Lymnaea stagnalis were studied during the first ten weeks after hatching. It is shown that these processes are atypical during early ontogenesis in comparison with adult mollusks. The obtained data on linear (height of shell) and weight growth can be equally well approximated with the von Bertalanffy equation or exponential and power equations. Both linear and weight growth are characterized by an approximately constant specific rate associated with synchronous oscillations of a week period. The oscillations were observed also for the oxygen consumption rate, but of another period (about 2.6 weeks). On average the metabolic rate after the initial triple increase during the first three days remains stable. The power coefficient of the allometric dependence of the total weight on the shell height is significantly less than that of the adult.     

Studies on avian erythrocyte metabolism. Effect of organic phosphates on oxygen affinity of embryonic and adult-type hemoglobins of the chick embryo.

The effects of 2,3 diphosphoglyceric acid (2,3-DPG), adenosine triphosphate (ATP), and inositol hexaphosphate (IHP) on the oxygen affinity of whole “stripped” hemoglobin (WSH), hemoglobin H (Hb-H), hemoglobin A (Hb-A) and hemoglobin D (Hb-D) isolated from 18-day chick embryo blood have been determined. The effect of the three organic phosphates upon the oxygen dissociation curves is similar and the following order of decreasing oxygen affinity of the organic phosphates was observed for each hemoglobin: 2,3-DPG < ATP < IHP. 2,3-DPG appears to have a slightly greater effect upon the P₅₀ of Hb-H than upon that of either of the two adult-type hemoglobins. However, this effect seems insufficient to suggest a preferential interaction of 2,3-DPG with Hb-H which would account for either the large amounts of 2,3-DPG in the erythrocytes of embryos or the higher oxygen affinity of the whole blood. The effects of the organic phosphates upon the Hill constant of the purified hemoglobins are variable. It is concluded that since the distribution of hemoglobins H, A, and D in the erythrocytes during the developmental period from 18-day embryos to 6-day chicks remains fairly constant, the previously described progressive decrease in oxygen affinity of the whole blood during this period results from changes in the total amount and distribution of the intraerythrocytic organic phosphates.²     

The development of photosynthesis in a greening mutant of chlorella and an analysis of the light saturation curve

Photosynthetic oxygen evolution considerably precedes the rise in chlorophyll during the greening of a yellow mutant of Chlorella vulgaris. Dark-grown cells required 20 times more light to saturate photosynthesis than light-grown or normal cells. The chlorophyll appears to add first to active reaction centers, then to fill in a more general antenna. The carotenoid pigments seem to add more randomly to the reaction centers. The shape of the light saturation curves can be explained with the assumption that an excitation in the antenna can reach several reaction centers. The efficiency of the total unit is constant during the greening process.     

Hypoxic effects on growth of Palaemonetes vulgaris larvae and other species: Using constant exposure data to estimate cyclic exposure response

First stage larval marsh grass shrimp, Palaemonetes vulgaris, were exposed to patterns of diurnal, semidiurnal, and constant hypoxia to evaluate effects on growth and to determine if there was a consistent relationship between exposures. A comparison of growth with cyclic exposures versus constant low dissolved oxygen (D.O.) concentrations equivalent to the minima of the cycles showed the cyclic exposures resulted in less growth impairment than constant low-D.O. exposures, when compared to saturated controls. The mean extent of growth impairment of cyclic hypoxia was, however, almost 1.5 times more than would be estimated using an arithmetic time-weighted-average of the hypoxic portion of the cycle. Additional testing with other life stages and species resulted in similar patterns of response. Based on this relationship, an adjusted time-weighted-average could be used to estimate field related responses to cyclic dissolved oxygen from laboratory-derived constant exposure data.     

Effect of Temperature on the Rate of Oxygen Consumption during the Second Half of Embryonic and Early Postembryonic Development of European Pond Turtle <Emphasis Type="Italic">Emys orbicularis</Emphasis> (Reptilia: Emydidae)

Oxygen consumption by eggs of European pond turtle was determined at two constant incubation temperatures of 25 and 28°C during the second half of embryogenesis. During development at both temperatures, the rate of oxygen consumption initially increased to remain constant during the last quarter of embryogenesis. The difference between the rates of oxygen consumption at these temperatures decreased during the studied period. The coefficient Q₁₀ for the rate of oxygen consumption decreased from 9 to 1.7. At an incubation temperature of 28°C, the changes in the rate of oxygen consumption in response to a short-term temperature decrease to 25°C or increase to 30°C depended on the developmental stage and were most pronounced at the beginning of the studied period. During late embryonic and first 2.5 months of postembryonic development, the rate of oxygen consumption did not significantly differ after such temperature changes. The regulatory mechanisms formed during embryonic development are proposed to maintain the level of oxygen consumption during temperature changes.     

Activity and respiration in the anemone, Metridium senile (L.) exposed to salinity fluctuations

Activity and respiration in the anemone, Metridium senile (L.), were monitored under both constant and fluctuating salinity conditions. During constant exposure to 50% sea water it was found that the animals retracted the tentacles and that the rate of oxygen consumption decreased by ≈50%. The same response was elicited from animals in 100% sea water in a contracted state. Animals exposed to continually fluctuating salinities were found to retract the tentacles, contract the body wall, and produce amounts of mucus during periods of decreasing salinities. These reactions were reversed during exposure to increasing salinity. Oxygen consumption never ceased entirely in animals exposed to dilute sea water and it was found that during declining oxygen tension M. senile regulated its oxygen consumption until the environmental oxygen tension fell to ≈30% saturation.     

SEASONAL VARIATION IN METABOLIC FUNCTIONS OF BRAMBLINGS

Seasonal variation in the rate of oxygen consumption during rest at different test temperatures and in the respiratory quotient (RQ) was observed in male Bramblings Fringilla montifringilla which had been caught as immature birds during autumn migration and kept under outdoor conditions for one year. Resting oxygen consumption measured from +31^o to – 4^oC during one night was significantly lower in late April and October (migratory seasons) as compared to the preceding and the following December. Because of marked seasonal changes in body weight, the significance of differences in metabolic rate between different seasons was largely dependent on the manner of expressing the rate of oxygen consumption, either per bird or as the 0–67 power of body weight (“surface coefficient”). The lower resting rate of oxygen consumption during the migratory seasons was interpreted as one possible factor responsible for allowing fat deposition by reducing total energy expenditure. This modification occurred only in birds kept under quasi-natural conditions outdoors and not in birds which were kept in cages under constant conditions of light and temperature in the laboratory.     

CARBON DIOXIDE PRODUCTION AND DURATION OF LIFE OF DROSOPHILA CULTURES

The total CO₂ produced by aseptic Drosophila cultures during the entire duration of life has been determined at 15°, 26°, and 30°C. in the dark and at 22–26°C. in the light. The total amount of CO₂ produced is not constant but is greater at 15° than at 26° or 30°, and is much greater in the light than in the dark. The total duration of life, therefore, is not determined by the time required to produce a limiting amount of CO₂.     

Dynamic model of vascular-targeted photodynamic therapy

Vascular-targeted photodynamic therapy has shown efficiency in treating port wine stains. A dynamic model that incorporates blood flow, kinetic diffusion, oxygen and photosensitizer consumption and reaction, and light modulation is proposed to reveal the interactions among light, photosensitizer, and oxygen. Simulation results show that pulse light modulation synchronized with heartbeats hold the advantage of increased singlet oxygen accumulation, higher oxygen concentration and lower temperature. Meanwhile, constant light treatment is advantageous in terms of higher temperature, lower total oxygen concentration and singlet oxygen accumulation. Therefore, the optimized treatment protocol may involve a balance among the phototoxicity, hypoxia, and photothermolysis.     

Intermediate metabolism during the ontogenetic development of Anastrepha fraterculus (Diptera: Tephritidae)

The fruit fly Anastrepha fraterculus is a major pest of native and exotic fruit trees in South America. Changes in weight, water content and metabolism were observed during its ontogenetic development in standard conditions (25 degrees C, RH=60% and 14 h:10 h photoperiod). The metabolic variables glycogen, total proteins, triglycerides and total lipids were measured by means of spectrophotometric methods. The results were correlated with pupae metamorphosis, temporal pattern, and beginning of adult life. Pupae were observed daily, and a sub-sample of 10 individuals was collected and maintained at -20 degrees C. The same procedure was performed with adults at 4 days after adult eclosion. Levels of total lipids and triglycerides were constant during pupal development, peaking in 312-h-old pupae. In 0-h-old pupae, glycogen levels were high, and decreased progressively until the insects were 312 h old. The peak in total proteins coincides with the post-histolysis period of the larval tissue (96-120 h). These results indicated that glycogen and proteins may be the principal sources of energy for metamorphosis. Total lipid and triglyceride contents remained steady during metamorphosis, and these were consumed in the first 4 days of adult life.     

Comparison of buffer and red blood cell perfusion of guinea pig heart oxygenation

Myocardial mean myoglobin oxygen saturation was determined spectroscopically from isolated guinea pig hearts perfused with red blood cells during increasing hypoxia. These experiments were undertaken to compare intracellular myoglobin oxygen saturation in isolated hearts perfused with a modest concentration of red blood cells (5% hematocrit) with intracellular myoglobin saturation previously reported from traditional buffer-perfused hearts. Studies were performed at 37 degrees C with hearts paced at 240 beats/min and a constant perfusion pressure of 80 cmH2O. It was found that during perfusion with a hematocrit of 5%, baseline mean myoglobin saturation was 93% compared with 72% during buffer perfusion. Mean myoglobin saturation, ventricular function, and oxygen consumption remained fairly constant for arterial perfusate oxygen tensions above 100 mmHg and then decreased precipitously below 100 mmHg. In contrast, mean myoglobin saturation, ventricular function, and oxygen consumption began to decrease even at high oxygen tension with buffer perfusion. The present results demonstrate that perfusion with 5% red blood cells in the perfusate increases the baseline mean myoglobin saturation and better preserves cardiac function at low oxygen tension relative to buffer perfusion. These results suggest that caution should be used in extrapolating intracellular oxygen dynamics from buffer-perfused to blood-perfused hearts.