A comparative study of hummingbirds and chickens provides mechanistic insight on the histidine containing dipeptide role in skeletal muscle metabolism

Histidine containing dipeptides (HCDs) have numerous ergogenic and therapeutic properties, but their primary role in skeletal muscle remains unclear. Potential functions include pH regulation, protection against reactive oxygen/nitrogen species, or Ca2+ regulation. In recognition of the challenge of isolating physiological processes in-vivo, we employed a comparative physiology approach to investigate the primary mechanism of HCD action in skeletal muscle. We selected two avian species (i.e., hummingbirds and chickens), who represented the extremes of the physiological processes in which HCDs are likely to function. Our findings indicate that HCDs are non-essential to the development of highly oxidative and contractile muscle, given their very low content in hummingbird skeletal tissue. In contrast, their abundance in the glycolytic chicken muscle, indicate that they are important in anaerobic bioenergetics as pH regulators. This evidence provides new insights on the HCD role in skeletal muscle, which could inform widespread interventions, from health to elite performance

Adaptations to salinity and osmoregulation in the frog Thoropa-miliaris (Amphibia, Leptodactylidae)

The leptodactylid frog Thoropa miliaris, from SE Brazil, may live on rocky marine shore, where it thrives on terrestrial and marine invertebrates, and often moves into the intertidal zone. The osmotic concentration of plasma, muscle homogenate and urine of the frogs freshly captured on the rocky shore was higher than those collected far from the sea, or kept in captivity for 6-8 months on a diet free of marine items. Increase in body urea and sodium concentrations, reported in amphibians as a response to hyperosmotic environment, was not found in T. miliaris. Osmotic concentration of the frogs from rocky shore was variable though, ranging from 400 to 980 mOsm/l. Such variation in the osmotic concentration may reflect a territorial behavior for foraging sites, which would result in higher intake of marine items by individuals living closer to intertidal zone

Whole-body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

The whole-body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non-shivering thermogenesis (NST) component of regulatory body heat originates differently in each group: from skeletal muscle in birds and from brown adipose tissue (BAT) in mammals. However, BAT is absent in monotremes, marsupials, and many eutherians, all whole-body endotherms. Indeed, recent research implies that BAT-driven NST originated more recently and that the biochemical processes driving muscle NST in birds, many modern mammals and the ancestors of both may be similar, deriving from controlled ‘slippage’ of Ca2+ from the sarcoplasmic reticulum Ca2+-ATPase (SERCA) in skeletal muscle, similar to a process seen in some fishes. This similarity prompted our realisation that the capacity for whole-body endothermy could even have pre-dated the divergence of Amniota into Synapsida and Sauropsida, leading us to hypothesise the homology of whole-body endothermy in birds and mammals, in contrast to the current assumption of their independent (convergent) evolution. To explore the extent of similarity between muscle NST in mammals and birds we undertook a detailed review of these processes and their control in each group. We found considerable but not complete similarity between them: in extant mammals the ‘slippage’ is controlled by the protein sarcolipin (SLN), in birds the SLN is slightly different structurally and its role in NST is not yet proved. However, considering the multi-millions of years since the separation of synapsids and diapsids, we consider that the similarity between NST production in birds and mammals is consistent with their whole-body endothermy being homologous. If so, we should expect to find evidence for it much earlier and more widespread among extinct amniotes than is currently recognised. Accordingly, we conducted an extensive survey of the palaeontological literature using established proxies. Fossil bone histology reveals evidence of sustained rapid growth rates indicating tachymetabolism. Large body size and erect stature indicate high systemic arterial blood pressures and four-chambered hearts, characteristic of tachymetabolism. Large nutrient foramina in long bones are indicative of high bone perfusion for rapid somatic growth and for repair of microfractures caused by intense locomotion. Obligate bipedality appeared early and only in whole-body endotherms. Isotopic profiles of fossil material indicate endothermic levels of body temperature. These proxies led us to compelling evidence for the widespread occurrence of whole-body endothermy among numerous extinct synapsids and sauropsids, and very early in each clade's family tree. These results are consistent with and support our hypothesis that tachymetabolic endothermy is plesiomorphic in Amniota. A hypothetical structure for the heart of the earliest endothermic amniotes is proposed. We conclude that there is strong evidence for whole-body endothermy being ancient and widespread among amniotes and that the similarity of biochemical processes driving muscle NST in extant birds and mammals strengthens the case for its plesiomorphy

Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia

The aim of this study was to describe the effect of hypoxia on whole body ion fluxes and hematological parameters in two Amazonian teleosts: Serrasalmus eigenmanni and Metynnis hypsauchen. The increase of Na+ and Cl- effluxes on M. hypsauchen exposed to hypoxia may be related to an increase of gill ventilation and effective respiratory surface area, to avoid a reduction in the oxygen uptake, and/or with the decrease of pHe, that could inhibit Na+ and Cl- transporters and, therefore, reduce influx of these ions. Effluxes of Na+ and Cl- were lower in hypoxia than in normoxia for S. eigenmanni, possibly because in hypoxia this species would reduce gill ventilation and oxygen uptake, which would lead to a decrease of gill ion efflux and, consequently, reducing ion loss. The increase on hematocrit (Ht) during hypoxia in M. hypsauchen probably was caused by an increase of the red blood cell volume (MCV). For S. eigenmanni the increase on glucose possibly results from the usage of glucose reserve mobilization. Metynnis hypsauchen showed to be more sensitive to hypoxia than Serrasalmus eigenmanni, since the first presented more significant alterations on these osmoregulatory and hematological parameters. Nevertheless, the alterations observed for both species are strategies adopted by fishes to preserve oxygen supply to metabolizing tissues during exposure to hypoxia

Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia

The aim of this study was to describe the effect of hypoxia on whole body ion fluxes and hematological parameters in two Amazonian teleosts: Serrasalmus eigenmanni and Metynnis hypsauchen. The increase of Na+ and Cl- effluxes on M. hypsauchen exposed to hypoxia may be related to an increase of gill ventilation and effective respiratory surface area, to avoid a reduction in the oxygen uptake, and/or with the decrease of pHe, that could inhibit Na+ and Cl- transporters and, therefore, reduce influx of these ions. Effluxes of Na+ and Cl- were lower in hypoxia than in normoxia for S. eigenmanni, possibly because in hypoxia this species would reduce gill ventilation and oxygen uptake, which would lead to a decrease of gill ion efflux and, consequently, reducing ion loss. The increase on hematocrit (Ht) during hypoxia in M. hypsauchen probably was caused by an increase of the red blood cell volume (MCV). For S. eigenmanni the increase on glucose possibly results from the usage of glucose reserve mobilization. Metynnis hypsauchen showed to be more sensitive to hypoxia than Serrasalmus eigenmanni, since the first presented more significant alterations on these osmoregulatory and hematological parameters. Nevertheless, the alterations observed for both species are strategies adopted by fishes to preserve oxygen supply to metabolizing tissues during exposure to hypoxia