Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

The peptide hormone ghrelin, also known as "hunger hormone", is primarily secreted by the stomach and plays a key role in the regulation of vertebrate appetite and energy balance. While the hunger hormone and its functions have been extensively researched in mammalian species, its physiological roles have received less attention in birds and knowledge on the ghrelin system is especially poor in wild avian species. In contrast to mammals, ghrelin acts as an anorexigenic signal in birds and suppresses food intake. In this study, we focussed on the altricial chicks of thin-billed prions (Pachyptila belcheri) which are subjected to irregular, up to 8 day-long fasts, while waiting for their parents to return from feeding trips. We show that thin-billed prion chicks, which received a meal in the night prior to sampling, had higher circulating ghrelin levels than fasting conspecifics. Ghrelin levels did not correlate with chick body condition, meal size, or the length of a fast. Our study adds to past literature supporting an anorexigenic effect of avian ghrelin and is among the first to describe ghrelin profiles in seabirds, thereby significantly contributing to the scarce literature on ghrelin in wild avian species.

Larvae of Galleria mellonella are well known for their parasitisation of honeybees, so developing new methods of controlling the pest population is an important issue. The present research examined the immunotoxic effects of 2-octenoic acid against wax moth larvae. The last instar larvae were used for all experimental analyses. The tested fatty acid doses LD50 and LD100 (9.66 µg/mg and 11.72 µg/mg of body mass) were applied topically to insects under in vivo conditions and the hemolymph was collected after 24 and 48 h. To check the in vitro impact of the 2-octenoic acid, the examined fatty acid was given directly to the cultured hemocytes (to a final concentration: 0.33 and 0.16 µg/µl) and incubated for 24 and 48 h. Current research using fluorescence microscopy and spectrofluorimetric measurements indicates the death of immunocompetent cells via the apoptosis pathway. Moreover, it shows the activation of caspases and an increase in the level of reactive oxygen/nitrogen damage after both in vivo and in vitro treatment of 2-octenoic acid. This points to the impact of both cellular and humoral elements on the immunological response to the toxic compound. Hence, 2-octenoic acid seems to have significant potential as an insecticide while being safe for humans and the environment. Therefore, further research into its potential is warranted.

Ischemia-reperfusion (I-R) injury represents a predominant etiology of acute kidney injury (AKI), for which effective treatments remain unavailable. In contrast, hibernating mammals exhibit notable resistance to cell death induced by I-R injury. However, the impact of I-R injury on cellular senescence-an important factor in AKI-has not been extensively studied in these species. Comparative biology may offer novel therapeutic insights. Renal proximal tubular epithelial cells (RPTECs) from the native hibernator Syrian hamster or mouse RPTECs were subjected to anoxia-reoxygenation. Proteins involved in DNA damage response (DDR) and cellular senescence were assessed using western blotting, reactive oxygen species (ROS) levels and cell death were quantified colorimetrically, and IL-6 with ELISA. Anoxia-reoxygenation induced oxidative stress in both mouse and hamster RPTECs; however, cell death was observed exclusively in mouse cells. While anoxia-reoxygenation elicited a DDR and subsequent senescence in mouse RPTECs, such responses were not detected in hamster RPTECs. Thus, RPTECs from the Syrian hamster exhibited increased ROS production upon reoxygenation but did not show DDR or cellular senescence. Further research is required to elucidate the specific protective molecular mechanisms in hibernators, which could potentially lead to the development of novel therapeutic approaches for I-R injury in non-hibernating species, including humans.

The knowledge about the occurrence and biochemical characteristics of key digestive enzymes is crucial for an enhanced understanding of the dietary ecophysiology of the species. On the other hand, integrative studies on digestive physiology and on tissue content of glycogen, glucose, lipid and protein in groups of ecological and economic importance are currently limited. In this work, we determined the occurrence and biochemical characteristics in intestine of key digestive enzymes activities as indexes of the ability to digest different dietary substrates and of functional differentiation for digestion/absorption of nutrients along with the intestinal coefficient as index of dietary habit and digestion efficiency in adults of Odonthtestes argentinensis inhabiting Mar Chiquita Coastal Lagoon (Buenos Aires, Argentina). Furthermore, to identify storage sites, glycogen, triglycerides and protein content in different tissues were also analyzed. The presence and biochemical characteristics of amylase, maltase, sucrase, lipase, trypsin and aminopeptidase-N activity in intestine, as well as the tissue content of glycogen, triglycerides and protein suggests that adults of O.argentinensis exhibit an adequate digestive battery to potentially perform complete hydrolysis of various dietary substrates and capacity for storage and/or utilization of energy reserves. Our study provides novel insights into the digestive/metabolic traits in adults of the resident silverside O. argentinensis from Mar Chiquita Coastal Lagoon.

Elasmobranchs are commonly carnivores and are important in energy transfer across marine ecosystems. Despite this, relatively few studies have examined the physiological underpinnings of nutrient acquisition in these animals. Here, we investigated the mechanisms of uptake at the spiral valve intestine for two representative amino acids (_L-alanine, _L-leucine) and one representative fatty acid (oleic acid), each common to the diet of a carnivore, the Pacific spiny dogfish (Squalus suckleyi). Transport was saturable for all three nutrients, depending upon transport calculation metric (i.e., mucosal disappearance, serosal appearance, or tissue accumulation). Over 0-10 mM range of amino acids the concentration at which ½ maximal transport occurred (K_m; a measure of transporter affinity) was 11.9 and 11.2 mM for tissue accumulation of alanine and leucine, respectively. Oleic acid transport was measured at lower concentrations (0-200 µM) and tissue accumulation did not reach saturation. Putative amino acid transport systems were delineated upon confirmation of sodium dependence and competitive inhibition with threonine, glycine, and lysine. The interplay of nutrient combinations on the modulation of nutrient acquisition rates, which better mimics the complex composition of both a meal and the internal osmolytes, was next investigated. Here, the application of serosal oleic acid led to diminished mucosal disappearance of leucine. Feeding did not significantly alter transport rates, perhaps indicative of maximal transport of these energy sources whenever the substrate is available given their importance both as metabolic fuels and precursors to the osmolyte urea.

We developed and validated a surgical technique to measure central venous pressure (CVP) in Nile tilapia, and investigated the effects of an acute temperature decrease (from 30 vs. 24 °C) and changes in heart rate (f_H) using zatebradine hydrocholoride, which decreases intrinsic f_H, on this species' cardiac function. As predicted, f_H and cardiac output ( $\dot{Q}$ ) were ~ 40% lower in the acutely cooled fish, and both groups had very comparable (i.e., within 10%) values for stroke volume (V_S)_. The CVP of fish acutely exposed to 24 °C was consistently ~ 0.04 kPa higher than in those measured at 30 °C across all concentrations of zatebradine (i.e., CVP increased from 0.04 to 0.11 kPa vs. - 0.01-0.07 kPa for 24 vs. 30 °C tilapia, respectively, as f_H was reduced). However, this did not result in an increase in V_S due to a right-shifted relationship between CVP and V_S for the 24 °C fish. These data suggest that the V_S of tilapia is less sensitive to changes/increases in CVP when temperature is acutely lowered, and that regardless of increases in preload (CVP), $\dot{Q}$ is primarily modulated by f_H in this species.

During the transition from fresh waters to terrestrial habitats, significant adaptive changes occurred in kidney function of vertebrates to cope with varying osmotic challenges. We investigated the mechanisms driving water conservation in the mammalian nephron, focusing on the relative contributions of active ion transport and Starling forces. We constructed a thermodynamic model to estimate the entropy generation associated with different processes within the nephron, and analyzed their relative importance in urine formation. We demonstrate that active ionic reabsorption exerts a pressure above 15,000 torr, a value more than 500 times greater than Starling forces. The entropy generation of the reabsorption process is found to be 20-fold higher than that of renal blood perfusion. These findings imply that the evolutionary history of vertebrates, particularly terrestrial mammals, has shaped the renal architecture to prioritize water conservation by means of an entropically costly process. This approach to the nephron function provides insights into the physiological adaptations of terrestrial vertebrates to conserve water and sheds light on the intricate interplay between environmental conditions and evolutionary responses in renal physiology.

The pirarucu is one of the very few obligate air-breathing fish, employing a gigantic, highly vascularized air-breathing organ (ABO). Traditionally, the ABO is thought to serve mainly for O₂ uptake (ṀO₂), with the gills providing the major route for excretion of CO₂ (ṀCO₂) and N-waste. However, under aquatic hypercapnia, a common occurrence in its natural environment, branchial ṀCO₂ to the water may become impaired. Under these conditions, does the ABO become an important route of ṀCO₂ excretion to the air? We have answered this question by measuring ṀCO₂ and ṀO₂ in both air and water phases, as well as the pattern of air-breathing, in pirarucu under aquatic normocapnia and hypercapnia (3% CO₂). Indeed, ṀCO₂ to the air phase via the ABO increased 2- to 3-fold during exposure to high water PCO₂, accounting for 59-71% of the total, with no change in the dominant contribution of the ABO to ṀO₂ (71-75% of the total). These adjustments were quickly reversed upon restoration of aquatic normocapnia. During aquatic hypercapnia, ṀCO₂ via the ABO became more effective over time, and the pattern of air-breathing changed, exhibiting increased frequency and decreased breath volume. Ammonia-N excretion (86-88% of total) dominated over urea-N excretion and tended to increase during exposure to aquatic hypercapnia. We conclude that the ability of the ABO to take on the dominant role in CO₂ excretion when required may have been an important driver in the original evolution of air-breathing, as well as in the functionality of the ABO in modern air-breathing fish.

Air-breathing vertebrates face many physiological challenges while breath-hold diving. In particular, they must endure intermittent periods of declining oxygen (O₂) stores, as well as the need to rapidly replenish depleted O₂ at the surface prior to their next dive. While many species show adaptive increases in the O₂ storage capacity of the blood or muscles, others increase the oxidative capacity of the muscles through changes in mitochondrial arrangement, abundance, or remodeling of key metabolic pathways. Here, we assess the diving phenotypes of two sympatric diving birds: the anhinga (Anhinga anhinga) and the double-crested cormorant (Nannopterum auritum). In each, we measured blood- and muscle-O₂ storage capacity, as well as phenotypic characteristics such as muscle fiber composition, capillarity, and mitochondrial arrangement and abundance in the primary flight (pectoralis) and swimming (gastrocnemius) muscles. Finally, we compared the maximal activities of 10 key enzymes in the pectoralis, gastrocnemius, and left ventricle of the heart to assess tissue level oxidative capacity and fuel use. Our results indicate that both species utilize enhanced muscle-O₂ stores over blood-O₂. This is most apparent in the large difference in available myoglobin in the gastrocnemius between the two species. Oxidative capacity varied significantly between the flight and swimming muscles and between the two species. However, both species showed lower oxidative capacity than expected compared to other diving birds. In particular, the anhinga exhibits a unique diving phenotype with a slightly higher reliance on glycolysis and lower aerobic ATP generation than double-crested cormorants.

Global warming is a major threat to reptiles because temperature strongly affects their development. High incubation temperatures reduce hatchling body size and physiological performance; however, its effects on brain development and learning abilities are less well understood. In particular, it remains unclear if the effects of elevated temperatures on learning are restricted to hatchlings or instead will persist later in life. To address this gap, we examined the effect of 'current' and 'future' (end-of-century, + 4 °C) incubation temperatures on hatchling and juvenile geckos Amalosia lesueurii, to test: (1) if elevated temperatures affect hatchling learning ability; (2) if the effects on learning persist in juvenile lizards, and (3) if and how elevated temperatures affect hatchling and juvenile brain anatomy and neuronal count. We found that fewer future-incubated hatchlings succeeded in the learning tasks. Nonetheless, the successful ones needed fewer trials to learn compared to current-incubated hatchlings, possibly due to a higher motivation. Reduced learning ability was still observed at the juvenile stage, but it did not differ between treatments due to a reduced cognitive performance of current-incubated juveniles. Future-incubated hatchlings had a smaller telencephalon, but this pattern was not found in juveniles. Neuron number and density in hatchlings or juveniles from both treatments were not different. Our results suggest that global warming will affect hatchling survival in the wild but it remains unclear if future-incubated lizards could compensate for the harmful effects of elevated temperatures. Further testing beyond the laboratory is required to understand whether phenotypic plasticity in lizards is sufficient to track global warming.