Cutaneous blood flow in the pigeon Columba livia: its possible relevance to cutaneous water evaporation.

The heat-acclimated rock pigeon is thought to use cutaneous water evaporation (CWE) as the 'preferred' route for heat dissipation, and this mechanism is controlled by adrenergic signaling. In the present study, we tested the hypothesis that adjustments in skin blood flow are a crucial component of this adaptation. Skin blood flow was measured by laser Doppler flowmetry and by ultrasonic flowmetry in heat-acclimated (HAc) and non-acclimated (NAc) pigeons. Skin blood flow, CWE and rectal and skin temperatures were measured under heat exposure (T(a)=50 degrees C) or following propranolol (1.3 mg kg(-1)) or clonidine (80 microg kg(-1)) administration. Using laser Doppler flowmetry, we found a significant increase (1.3-fold) in skin blood flow in the dorsal skin of HAc pigeons following propanolol administration. In contrast, a significant decrease (0.7-fold) was observed in NAc birds. Injection of clonidine resulted in a significant decrease in skin blood flow in both HAc and NAc pigeons (0.4- and 0.5-fold, respectively). Heat exposure increased blood perfusion in both groups (2.5- and 1.8-fold, respectively). Using ultrasonic flowmetry, we showed that both propanolol and clonidine increase the arterial blood flow (Q(a)) in HAc pigeons, while venous blood flow (Q(v)) decreases. In contrast, no significant changes were found in NAc pigeons. As shown by the effect of clonidine, augmentation of skin blood flow is not a prerequisite for CWE, but normally coincides with a greater difference in arterial-venous pressure. Possible regulatory mechanisms are discussed.

Cardiovascular responses to adrenergic agents in different acclimation states in the rock pigeon (Columba livia).

The effect of propranolol on heart rate (fH) was measured in season-acclimatized pigeons. Propranolol treatment decreased fH in winter-acclimatized pigeons, accelerated fH in summer-acclimatized pigeons, but had no effect on fH in spring-acclimatized pigeons. The effect of propranolol in summer-acclimatized pigeons is opposite to that observed in mammals. Interestingly, isoproterenol produced a propranolol-like cardioacceleration in heat-acclimated pigeons. We suggest that propranolol affects fH in summer-acclimatized pigeons via two opposing routes-a direct and a peripheral indirect route. We also suggest that the cardiovascular effects of propranolol are involved in the capacity of the pigeon to evaporate water from its skin.

Ozone treatment affects pigment precursor metabolism in pine seedlings.

Five-week-old seedlings of Pinus halepensis Mill. and Pinus brutia Ten. were exposed to air polluted with ozone (O3) (250 nl l-1, 12 h day-1 for 4 days) or to ambient air containing ca 10-20 nl l-1 O3, in the light (180 &mgr;mol m-2 s-1 photosynthetic photon flux density [PPFD], 12 h day-1) and then fed for 24 h in the light (100 &mgr;mol m-2 s-1 PPFD) with various radioactive precursors of chlorophyll (Chl) and carotene biosynthesis: 5-[4-14C]-aminolevulinic acid (14C-ALA), L-[14C(U)]-glutamic acid (14C-Glu), or D,L-[2-14C]-mevalonic acid (14C-MVA). Pigments were then extracted from cotyledons and fully expanded needles. Chl a and carotene were separated by thin-layer chromatography and high-performance liquid chromatography and their specific activities were determined. 14C-ALA and 14C-Glu labels were incorporated into Chl a and carotene. Exposure to O3 did not inhibit incorporation of 14C-ALA into Chl a molecules, but hydrolysis of Chl a showed that O3 inhibited phytol labelling of Chl a. Labelling of carotene was also inhibited by O3, but not when 14C-MVA was used as the label. These data suggest that O3 treatment inhibits (directly or indirectly) the biosynthesis of isoprenoids from products of ALA and Glu metabolism in the plastid, but not from MVA in the cytosol. This inhibition was more prominent when 14C-ALA was used as the label than when 14C-Glu was the labelling precursor. A significant increase in pheophorbide a, a tetrapyrrole component of Chl a labelling, and a concomitant decrease in phytol labelling was observed following incubation of O3-treated pine seedlings with 14C-ALA and 14C-Glu. Stronger inhibition of carotene biosynthesis and activation of Chl a tetrapyrrole labelling by 14C-ALA (in comparison with 14C-Glu) indicated that exposure to O3 inhibits the conversion of ALA to Glu as the first step in ALA catabolism. These results also suggested a more intensive Glu metabolism (in comparison with ALA) for carotene biosynthesis in the cytosol, as well as cooperation between two pathways of isopentenyl diphosphate biosynthesis.

Synergistic effects of a photooxidized polycyclic aromatic hydrocarbon and copper on photosynthesis and plant growth: evidence that in vivo formation of reactive oxygen species is a mechanism of copper toxicity.

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) are often cocontaminants in industrialized environments, yet little is known about either the extent or mechanisms of their cotoxicity. To address this shortfall, the combined effects of an oxygenated PAH, 1,2-dihydroxyanthraquinone (1,2-dhATQ), and a heavy metal, Cu2+, on photosynthesis and growth of the duckweed (Lemna gibba) were evaluated. Using assays of chlorophyll a fluorescence and photosystem I activity, 1,2-dhATQ inhibited electron transport at the cytochrome b6/f complex. Conversely, Cu2+ alone (at low concentrations) had little effect on photosynthesis. When Cu2+ was combined with 1,2-dhATQ, an increase in transient and steady-state chlorophyll a fluorescence quenching occurred relative to 1,2-dhATQ alone. Treatment of isolated thylakoid membranes with 1,2-dhATQ inhibited whole-chain linear electron transport, measured as O2 consumption using methyl viologen as the electron acceptor. However, Cu2+ plus 1,2-dhATQ resulted in active O2 consumption with or without methyl viologen as an electron acceptor. From these data, we conclude that 1,2-dhATQ renders the plastoquinone pool to a highly reduced state by inhibiting at cytochrome b6/f. Then, Cu2+ is able to mediate the transfer of electrons from reduced plastoquinone to O2, forming reactive oxygen species. At the whole-organism level, when Cu2+ and 1,2-dhATQ were mixed at concentrations that resulted in the above-mentioned impacts on photosynthesis, synergistic inhibition of plant growth was observed. This suggests a catalytic mechanism of toxicity for redox active metals, a process that could be instrumental in explaining their impacts at low concentrations.

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation.

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.

New experimental test of the pauli exclusion principle using accelerator mass spectrometry

We report the results of a new experimental search for the Pauli-forbidden 1s(4) state of Be, denoted by Be ('). Using the Accelerator Mass Spectrometer facility at Purdue University, we set limits on the abundance of Be (') in metallic Be, Be ore, natural gas, and air. Our results improve on those obtained in a previous search for Be (') by a factor of approximately 300.

Oxygen uptake photosensitized by disorganized chlorophyll in model systems and thylakoids of greening barley.

Light-dependent oxygen uptake was observed and studied in thylakoids from early greening barley in comparison to oxygen uptake in chlorophyll solutions and in thylakoids from fully green leaves. Substantial oxygen uptake was observed in chlorophyll solutions supplemented with tryptophan, histidine, ascorbic acid or linoleic acid. This uptake was diminished by adding azide, beta-carotene and alpha-tocopherol, which are specific singlet-oxygen quenchers. Illuminated thylakoids from greening barley also exhibited marked oxygen uptake that, likewise, was strongly quenched by azide. In comparison, azide was found not to affect oxygen uptake that is associated with the methyl viologen-catalyzed Mehler reaction. It is reasoned that in the first two cases the oxygen uptake arises from chlorophyll-photosensitized activation of oxygen to the singlet state and its consumption by exogenous or endogenous substrates. In greening, we propose that disorganized chlorophyll photo-sensitizes the oxygen uptake.

The role of beta-adrenergic receptors in the cutaneous water evaporation mechanism in the heat-acclimated pigeon (Columba livia).

The effects of selective and non-selective beta-adrenergic agents on cutaneous water evaporation (CWE) were studied in hand-reared rock pigeons (Columba livia). CWE was measured by the vapor diffusive resistance method, using a transient porometer. Intramuscular and subcutaneous injections of a non-selective beta-adrenergic antagonist (propranolol) or a selective beta(2)-adrenergic antagonist (ICI-118551) to heat-acclimated (HAc) pigeons at ambient temperature (T(a)) of 24 degrees C resulted in intensive CWE. The CWE values that were triggered by propranolol and ICI-118551 (18.59+/-0.73 and 16.48+/-0.70 mg cm(-2) h(-1), respectively) were close to those induced by heat exposure (17.62+/-1.40 mg cm(-2) h(-1)). Subcutaneous administration of propranolol produced local response. Intramuscular injection of salbutamol (selective beta(2)-adrenergic agonist) to HAc pigeons drastically diminished CWE induced by either propranolol, metoprolol or heat exposure. Such manipulations also enhanced panting at relatively low T(a)s (42 degrees C). The inhibition of beta(1)-adrenergic receptors by metoprolol increased CWE, while inhibition by atenolol produced no change from basal values. This difference may be attributed to their distinctive nature in penetrating the blood-brain barrier. Our findings indicate a regulatory pathway for CWE consisting of both beta(1)- and beta(2)-adrenergic receptors. We suggest that the beta(1)-adrenergic effect is restricted mainly to the CNS, while the beta(2)-adrenergic effect takes place at the effector level. We postulate this level to be either the cutaneous microvasculature or the epidermal layer.

Heat stress induces ultrastructural changes in cutaneous capillary wall of heat-acclimated rock pigeon.

In heat-acclimated rock pigeons, cutaneous water evaporation is the major cooling mechanism when exposed at rest to an extremely hot environment of 50-60 degrees C. This evaporative pathway is also activated in room temperature by a beta-adrenergic antagonist (propranolol) or an alpha-adrenergic agonist (clonidine) and inhibited by a beta-adrenergic agonist (isoproterenol). In contrast, neither heat exposure nor drug administration activates cutaneous evaporation in cold-acclimated pigeons. To elucidate the mechanisms underlying this phenomenon, we studied the role of the ultrastructure and permeability of the cutaneous vasculature. During both heat stress and the administration of propranolol and clonidine, we observed increased capillary fenestration and endothelial gaps. Similarly, propranolol increased the extravasation of Evans blue-labeled albumin in the skin tissue. We concluded that heat acclimation reinforces a mechanism by which the activation of adrenergic signal transduction pathways alters microvessel permeability during heat stress. Consequently the flux of plasma proteins and water into the interstitial space is accelerated, providing an interstitial source of water for sustained cutaneous evaporative cooling.

How to stay cool in a hot desert--a lesson from the rock pigeon.

This review presents an overview of the puzzle called "cutaneous water evaporation (CWE) cooling mechanism" in birds. Heat acclimation of the rock pigeon induces cellular modifications that affect the myocardium, cutaneous vasculature, and the epidermis, and hence enable the initiation of CWE. These cells are the targets for adrenergic signals that participate in the mechanism that controls the initiation and intensity of CWE. As a result the cardiac performance of the heat acclimated pigeon is intensified in response to adrenergic agents, and peripheral blood vessels and the epidermis both increase their permeability in response to heat stress. The CWE cooling mechanism is more economical in terms of water conservation, and provides more efficient protection to its owner, compared to the 'classic' respiratory cooling mechanism. Moreover, current data present the rock pigeon--a small diurnal homeotherm--as a classic model for a desert bird.

Adaptive changes in the epidermal structure of the heat-acclimated rock pigeon (Columba livia): A comparative electron microscopy study.

The purpose of this study was to find out whether the microstructure of the highly permeable skin of heat-acclimated pigeons allowing increased evaporative cooling differs from the skin of pigeons in the non-acclimated or cold-acclimated state. In addition, the correlation between epidermal morphology and cutaneous water evaporation in heat-acclimated pigeons was elucidated. The epidermis of heat-acclimated pigeons differs in several respects from the epidermis of non-acclimated or cold-acclimated birds. Both the dorsal and the abdominal skin include modified areas, characterized by increased vascularization, epidermis with greater thickness, and changes in intracellular structures. Greater thickness results from hypertrophy of epidermal cells possibly due to greater fluid content of the sebokeratinocytes in the germinative layers. The stratum corneum includes corneocytes with thickened cornified envelopes and contains greater mass of keratin-complex material compared to non-acclimated and cold-acclimated pigeons. The extracellular space between the compactly piled corneocytes contains amorphous lipoid material. The multigranular bodies lack compact organization of lipid bilayers. The transitional layer in the heat-acclimated pigeon displays atypical keratohyalin granules, which are multilateral and dendritic in shape. It is concluded that the dorsal and abdominal skin of heat-acclimated pigeons contains areas that differ in structure from their counterparts in non-acclimated and cold-acclimated pigeons. The structural characteristics of these modified patches suggest a high rate of cutaneous evaporation and decreased skin resistance to transepidermal diffusion of water vapor. Thus, the skin of a heat-acclimated pigeon responds to the thermoregulatory requirements for increased cutaneous water evaporation by structural changes. J. Morphol. 235:17-29, 1998. © 1998 Wiley-Liss, Inc.

Determination of catabolism of the photosystem II D 1 subunit by structural motifs in the polypeptide sequence.

Proteolytic mapping of the D 1 subunit of photosystem two and a degradation product which arises during its rapid catabolism shows that the latter is a result of proteolysis within the peptide motif QEEET. This motif is located in a portion of the D 1 protein thought to form a stroma-exposed connection between fourth and fifth transmembrane segments. This connection domain also contains a "PEST"-like sequence and forms part of the QB/herbicide binding niche. The QEEET motif seems to provide a major epitope in immunological studies, as judged from reaction of D 1 and its fragments with polyclonal antibodies. Antibodies against D 1 were found to react with other animal and plant proteins which contain similar sequence motifs.

The effect of heat exposure on blood chemistry of the hyperthermic rabbit.

1. Two hours of exposure to heat stress, resulted in hyperthermia in rabbits (Oryctolagus cuniculus). 2. This was accompanied by a severe hypocapnia, partly compensated for by a significant decrease in bicarbonate (HCO3-) concentration. 3. The severest hyperthermia (Tb = 43.5 degrees) was followed by a sharp decreased in both PaCO2 (to 20.2 torr) and HCO3- (to 9.2 mM/l), resulting in extreme metabolic acidosis (pH = 7.290). 4. The significant increase in serum osmolality (27%) is interpreted by the cumulative effect of increased electrolyte and metabolite concentrations. 5. The elevation in blood BUN, creatinine, globulin and GOT levels point to a possible damage to muscle cells by hypothermia. 6. The stable cholesterol and alkaline phosphatase levels, suggest that liver tissue was not damaged. 7. The dramatic increase in glucose from 103.8 to 348.8 mg%, and the significant increase (from 22.0 to 39.9 mg%) in BUN, suggest a possible disability of the cells to metabolize carbohydrates, accompanied by a progressive proteolysis as an alternative process for energy production. 8. The data suggest that the emergence of muscle cell damage, severe hyperglycemia and acidosis under heat stress, precedes and amplifies the deteriorating effects of high Tb in heat stressed rabbits, which often lead to mortality.

Osmoregulation and body fluid compartmentalization in dehydrated heat-exposed pigeons.

Osmoregulatory and volume-regulatory responses of heat-acclimated pigeons (Columba livia) were studied during normal hydration and dehydration combined with heat exposure. Dehydrated heat-exposed pigeons (exposure to 50 degrees C following 48 h of water deprivation; 16-18% mass loss) could recover 97% of their initial body mass within 30 min of free drinking at the end of heat exposure. At the end of heat exposure, body temperature increased by 3 degrees C and hematocrit increased by 12.5%. Serum electrolyte and protein concentrations increased by 33-53% (P less than 0.001). Serum osmolality reached an outstanding mean value of 436.7 +/- 28.5 mosmol/kg (n = 11), 30.5% higher than the normal mean value. Serum glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase concentrations did not change during dehydration, suggesting no impairment in circulatory function. Blood urea nitrogen increased sixfold, indicating a total shutdown of the kidney. Relative plasma volume was maintained during dehydration at the expense of extravascular spaces and with a decreased vascular permeability as indicated by the increase in Evans blue-labeled albumin half-life (control, 104 +/- 53 min; dehydration, approaching infinity). Altogether, extracellular fluid volume and intracellular fluid volume contributed 53 and 47% of the evaporative water loss, respectively. It is concluded that plasma volume regulation may play an important role in the effective thermoregulatory responses of heat-exposed dehydrated pigeons. This regulation is achieved by preferential shifts of body water reserves among the various body water compartments coinciding with a remarkable tolerance to high osmotic pressures.

Panting and acid-base regulation in heat stressed birds.

1. Studies in respiratory physiology and acid-base balance of panting birds exposed to high Tas show that flying as well as nonflying birds can use the respiratory system simultaneously for gas exchange and evaporative cooling. 2. The present study proves that well acclimated hand-reared birds can effectively regulate a normal CO2 level and acid-base status in arterial blood, when exposed to extremely high temperatures (50-60 degrees C). 3. In many birds practising simple or "flush-out" panting, the dead space can be reduced to a volume which is estimated to be approx 15% the volume of the respiratory tract. 4. These two modes of ventilation, shallow and high-rate, restricted to the nonrespiratory surfaces, may ensure the avoidance of CO2-washout and limit lung ventilation to the volumes needed for oxygen consumption. 5. This view supports earlier theories, suggesting the existence of physiological shunt mechanisms which operate during thermal panting in birds.

Reproduction of rock pigeon exposed to extreme ambient temperatures.

1. The breeding biology of rock pigeon (Columba livia) exposed to ambient temperatures (Ta) between 50 and 60 degrees C was investigated. 2. Four families accomplished three complete life cycles after long term daily exposure to extreme Ta, with about 100% success. 3. The steady state temperatures in the nest were 60, 58, 53 and 44.6 degrees C in the air, substrate surface, underwing, and in the egg's microenvironment, respectively. 4. At thermal conditions between 30 and 60 degrees C, egg temperature (Tegg) was regulated between 36.8 +/- 0.8 (S.D.) and 41.7 +/- 0.4 (S.D.). Tegg increases by 0.163 degrees C/1 degree C rise in Ta. 5. Mean Tb of the nonincubating parent exposed to 30-60 degrees C is 41.6 +/- 0.6 degrees C (S.D.). Under the same conditions the incubating parent regulated a significantly (P less than 0.01) lower Tb (38.8 degrees C) at 45 degrees C Ta and about 1 degree C lower Tb at 30 and 60 degrees C Ta, respectively. 6. By comparing the differences between fast (5 min) cooling of hot egg (44.8 degrees C) to slow heating (60-90 min), we could demonstrate the high sensitivity of the incubating parent to the danger of embryo overheating. 7. The significance of the adaptive behavioral and physiological mechanisms in breeding under extreme thermal conditions are discussed.

Degradation of the 32 kD Herbicide Binding Protein in Far Red Light.

White light (400-700 nanometers) supports the activity of photosystem I (PSI) and photosystem II while far red light (>/=700 nanometers) supports PSI almost exclusively. In intact fronds of Spirodela oligorrhiza, turnover of the 32 kilodaltons herbicide binding protein is stimulated under both these light conditions, although not in the dark or at wavelengths >730 nanometers. As is the case in white light, the far red light induced degradation of the protein is inhibited by DCMU. The means by which far red light operates is unclear. Hypotheses considered include: PSI activated proteolysis, PSI-induced formation of semiquinone anions, and PSI-generated free radicals.

The heat-acclimated pigeon: an ideal physiological model for a desert bird.

Acclimation of rock pigeon (Columba livia) to high ambient temperature (Ta) 50 degrees C from the time of hatching resulted in a well-developed cutaneous evaporative cooling mechanism (CECM), which became the dominant mechanism for heat dissipation. After the age of 15 days and in adults, acclimated pigeons exposed to 48-60 degrees C Ta could regulate normal body temperature (Tb) without employing either panting or gular fluttering. Respiration rate varied between 36 +/- 12 (SD) and 35 +/- 14 breaths/min at moderate and at extreme high Ta's, respectively. During thermal stress (42, 45, and 47 degrees C) imposed in a metabolic chamber, nonpanting pigeons' heat balance was achieved by adjusting low-level heat production (46.2 +/- 6.8 W/m2) and by use of an efficient CECM that dissipated 145% of the metabolic heat. Tb was regulated between 40.7 +/- 0.5 and 41.8 +/- 0.4 degrees C over a wide range of Ta's (20-56 degrees C). The respiratory evaporative cooling mechanism (RECM) was effective since hatching. The CECM developed approximately 24 h later during the ontogeny of the altricial nestling pigeon. This trait, which exists in many bird species and may be a recent development, possibly evolved as an adaptation to hot environments. In the present study we have brought evidence for a multitrait physiological adaptation that takes preeminence in adjusting the processes involved in maintaining heat balance. This integrative complex creates a powerful, efficient tool for contending with the most extreme thermal conditions.

Identification of psbA and psbD gene products, D1 and D2, as reaction centre proteins of photosystem 2.

A recent report (Nanba O, Satoh K: Proc. Natl. Acad. Sci. USA 84: 109-112, 1987) described the isolation from spinach of a putative photosystem 2 reaction centre which contained cytochrome b-559 and three other electrophoretically resolvable polypeptide bands, two of which have molecular weights comparable to the D1 and D2 polypeptides. We have used in vivo labelling with radioactive methionine and probed with D1 and D2 monospecific antibodies (raised against synthetically expressed sequences of the psbA and psbD genes) for specific detection of these proteins in a similarly prepared photosystem 2 reaction centre preparation. These techniques identified a 32 000 dalton D1 band, a 30 000 dalton D2 band and a 55 000 dalton D1/D2 aggregate, the latter apparently arising from the detergent treatments employed. Digestions with a lysine-specific protease further confirmed the identification of the lysine-free D1 polypeptide and also confirmed that the D1 molecules in the 55 000 dalton band were in aggregation with other bands and not in self-aggregates. The D1 and D2 polypeptides (including the aggregate) are considerably enriched in the photosystem two reaction centre preparation compared to the other resolved fractions.