Jordi Altimiras

Gastrointestinal blood flow and postprandial metabolism in swimming sea bass Dicentrarchus labrax.

In trout and salmon, the metabolic costs of exercise and feeding are additive, which would suggest that gastrointestinal blood flow during exercise is maintained to preserve digestive and absorptive processes related to the specific dynamic action (SDA) of food. However, in most published studies, gastrointestinal blood flow drops during swimming, hypoxia, and general stress. To test whether gastrointestinal blood flow is spared during exercise after feeding, sea bass were instrumented with flow probes to measure cardiac output and celiacomesenteric blood flow while swimming in a respirometer before and after feeding. Swimming at 2 body lengths per second (bl s−1) increased metabolic rate considerably more than did feeding (208% vs. 32% increase, respectively, relative to resting), and a similar pattern was observed for cardiac output. In unfed fish, resting gastrointestinal blood flow was 13.8 ± 0.5 mL min−1 kg−1. After feeding, resting gastrointestinal blood flow increased by 82% but then decreased progressively with increasing swimming speeds. At 2 bl s−1, gastrointestinal blood flow in fed fish was not significantly different compared with that in unfed swimming fish, and, therefore, the data do not support the gastrointestinal sparing hypothesis. The magnitude of the SDA was maintained despite the decrease in gastrointestinal blood flow and the consequent reduction in oxygen supply to the gut. An estimate of maximal oxygen flow to the gastrointestinal tract after feeding yielded 2.6 mmol O2 h−1 kg−1, but this amount is not able to cover the oxygen demand of 3.16 mmol O2 h−1 kg−1. Therefore, the SDA must reflect metabolic processes in tissues other than those directly perfused by the celiacomesenteric artery.

SEX DIFFERENCES IN THE HEART RATE VARIABILITY SPECTRUM OF FREE-SWIMMING ATLANTIC SALMON (SALMO SALAR L.) DURING THE SPAWNING SEASON

Heart rates were telemetered from male and female adult salmon (Salmo salar L.) when they were ascending a river to spawn. In this specific period, males had higher heart rates than females, reflecting the higher activity levels and higher metabolic rates of the males. Analysis of the beat-to-beat intervals (using the heart rate variability spectrum) revealed a single spectral peak that differed between sexes, with males displaying a spectral peak at lower frequencies than females even when the heart rate was the same. The dual spectral peak observed in higher vertebrates and in some other studies in fish was not found. It is suggested that the single spectral peak is related to the activity of the blood pressure control loop. In this framework, the gender spectral differences could be explained by a differential vascular reactivity related to different sex steroid concentrations in plasma. Spectral analysis of beat-to-beat intervals is extensively used to understand short-term control of heart rate in mammals; this study indicates that it can also be applied to free-living fish to understand neural cardiovascular regulation.

Sensitivity of organ growth to chronically low oxygen levels during incubation in Red Junglefowl and domesticated chicken breeds

Genetic selection programs have imposed large phenotypic changes in domesticated chicken breeds that are also apparent during embryonic development. Broilers, for example, have a faster growth rate before hatching in comparison with White Leghorns, indicating that the allocation of resources toward different functions already begins before hatching. Therefore, we hypothesized that embryonic organ growth would follow different developmental trajectories and would be differentially affected by an oxygen shortage during incubation. Heart, brain, and liver growth were studied in broiler, White Leghorn, and Red Junglefowl embryos at embryonic (E) ages E11, E13, E15, E18, and E20, and the results were fitted to growth allometric equations to determine the degree of organ stunting or sparing caused by low oxygen during incubation. Hypoxia caused a 3-fold larger mortality in Red Junglefowl than in the domesticated breeds, with a similar impairment of embryonic growth of 18%, coupled with a reduction in yolk utilization of 56%. Relative brain size was not affected by hypoxia in any breed, but a substantial stunting effect was observed for the liver and heart at late embryonic ages, with marked differences between breeds. In Red Junglefowl, only the heart was stunted. In White Leghorns, only the liver was stunted, and in broilers, both organs were stunted. These results can be explained in terms of the selection pressure on long-term production traits (reproductive effort) in White Leghorns, requiring a more efficient lipid metabolism, compared with the selection pressure on shorter-term production traits (growth) in broilers, requiring overall metabolic turnover and convective nutrient delivery to all tissues. At the same time, a remarkable sparing of the heart was observed in broilers and Red Junglefowl between E11 and E15, which suggests that cardiac growth can be manipulated during embryonic development. This result could be relevant for manipulating the phenotype of the heart for management purposes at a developmental stage when the bird is most versatile and phenotypically malleable.

Is domestication driven by reduced fear of humans? Boldness, metabolism and serotonin levels in divergently selected red junglefowl (Gallus gallus).

Domesticated animals tend to develop a coherent set of phenotypic traits. Tameness could be a central underlying factor driving this, and we therefore selected red junglefowl, ancestors of all domestic chickens, for high or low fear of humans during six generations. We measured basal metabolic rate (BMR), feed efficiency, boldness in a novel object (NO) test, corticosterone reactivity and basal serotonin levels (related to fearfulness) in birds from the fifth and sixth generation of the high- and low-fear lines, respectively (44–48 individuals). Corticosterone response to physical restraint did not differ between selection lines. However, BMR was higher in low-fear birds, as was feed efficiency. Low-fear males had higher plasma levels of serotonin and both low-fear males and females were bolder in an NO test. The results show that many aspects of the domesticated phenotype may have developed as correlated responses to reduced fear of humans, an essential trait for successful domestication.

Prenatal hypoxia programs changes in β-adrenergic signaling and postnatal cardiac contractile dysfunction

Prenatal hypoxia leads to an increased risk of adult cardiovascular disease. We have previously demonstrated a programming effect of prenatal hypoxia on the cardiac β-adrenergic (βAR) response. The aim of this study was to determine 1) whether the decrease in βAR sensitivity in prenatally hypoxic 5-wk old chicken hearts is linked to changes in β1AR/β2ARs, Gαi expression and cAMP accumulation and 2) whether prenatal hypoxia has an effect on heart function in vivo. We incubated eggs in normoxia (N, 21% O2) or hypoxia from day 0 (H, 14% O2) and raised the posthatchlings to 5 wk of age. Cardiac β1AR/β2ARs were assessed through competitive binding of [(3)H]CGP-12177 with specific β1AR or β2AR blockers. Gαs and Gαi proteins were assessed by Western blot and cAMP accumulation by ELISA. Echocardiograms were recorded in anesthetized birds to evaluate diastolic/systolic diameter and heart rate and tissue sections were stained for collagen. We found an increase in relative heart mass, β1ARs, and Gαs in prenatally hypoxic hearts. cAMP levels after isoproterenol stimulation and collagen content was not changed in H compared with N, but in vivo echocardiograms showed systolic contractile dysfunction. The changes in βAR and G protein subtypes may be indicative of an early compensatory stage in the progression of cardiac dysfunction, further supported by the cardiac hypertrophy and systolic contractile dysfunction. We suggest that it is not the changes in the proximal part of the βAR system that causes the decreased cardiac contractility, but Ca(2+) handling mechanisms further downstream in the βAR signaling cascade.

Fetal development of baroreflex sensitivity: The chicken embryo as a case model

The baroreflex is the main short term compensatory mechanism to buffer blood pressure changes and maintain circulatory homeostasis. Its ontogeny and importance during prenatal life is not fully understood so we used broiler chickens to investigate the maturation of the baroreflex in late incubation using a novel method that measured changes in heart rate during spontaneous fluctuations in blood pressure. Our results suggest that a baroreflex is already functional at d17 with no indication of further maturation in terms of sensitivity (gain at 17 d was 52.9±8.3 and at 20 d 69.5±16.2 ms kPa(-1)). The physiological relevance of these values is shown using data surrogation methods. Although the results contrast with the progressive baroreflex maturation indicated by the pharmacological method, we sustain that both methods provide information on baroreflex regulation. While the spontaneous method evaluates truly physiological (but small) pressure changes, the pharmacological method provides a more consistent and repetitive challenge for the reflex that requires a different recruitment of baroreflex effectors.

Ontogeny of vocalizations and movements in response to cooling in chickens fetuses.

Bird incubation demands a balance between parental needs for foraging with fetal needs for heat provision and protection so that any means of communication between the fetus and the parents would have an adaptive value. The aim of the study was to investigate whether putative avenues of feto-maternal communication would correlate to physiological changes caused by environmental alterations. Oxygen consumption was used as an indicator of fetal well being. The frequency, duration, intensity and composition of fetal vocalizations and the frequency and intensity of movements were used to evaluate the potential for communicating fetal status quo. Fetuses of broiler chickens (Gallus gallus domesticus) at three developmental stages (day 18, internally pipped and externally pipped) were challenged by a stepwise reduction in ambient temperature down to 30 degrees C. A drop in oxygen consumption in response to lowered temperatures was found in all stages. No differences correlating with temperature variations were found in any of the variables associated with fetal vocalization, even if externally pipped fetuses vocalized more than internally pipped fetuses. Movement occurrence and movement intensity, however, increased initially and decreased at temperatures below 35.0-35.5 degrees C. Considering that the lower limit of optimal development is between 35 and 36 degrees C, the results suggest that fetal movements can be of potential use to the incubating parent to assess and protect the well-being of the fetus.

Chronic hypoxia during development does not trigger pathologic remodeling of the chicken embryonic heart but reduces cardiomyocyte number

Fetal growth restriction programs an increased risk of cardiovascular disease in adulthood, but the actual mechanisms of this developmental programming are not fully understood. Previous studies in mammalian models suggest that hearts of growth-restricted fetuses have reduced cardiomyocyte number due to reduced proliferation and premature cardiomyocyte maturation. Chicken embryos incubated under chronic hypoxia are also growth-restricted, have smaller hearts, and show signs of cardiac insufficiency posthatching. The aim of the present study was to investigate how chronic hypoxia (14% O2) during development affects cardiomyocyte mass and how myocardial structure is altered. Hypoxic incubation reproduced the well-characterized embryonic growth restriction and an increased ventricle-to-body mass ratio (at E11, E15, E17, and E19) with reduced absolute heart mass only at E19. Cell density, apoptosis, and cardiomyocyte size were insensitive to hypoxia at E15 and E19, and no signs of ventricular wall remodeling or myocardial fibrosis were detected. Bayesian modeling provided strong support for hypoxia affecting absolute mass and proliferation rates at E15, indicating that the growth impairment, at least partly, occurs earlier in development. Neither E15 nor E19 hearts contained binucleated cardiomyocytes, indicating that fetal hypoxia does not trigger early maturation of cardiomyocytes in the chicken, which contrasts with previous results from hypoxic rat pups. In conclusion, prenatal hypoxia in the chick embryo results in a reduction in the number of cardiomyocytes without inducing ventricular remodeling, cell hypertrophy, or premature cardiomyocyte maturation.

Mathematical modeling improves EC50 estimations from classical dose–response curves

The β‐adrenergic response is impaired in failing hearts. When studying β‐adrenergic function in vitro, the half‐maximal effective concentration (EC50) is an important measure of ligand response. We previously measured the in vitro contraction force response of chicken heart tissue to increasing concentrations of adrenaline, and observed a decreasing response at high concentrations. The classical interpretation of such data is to assume a maximal response before the decrease, and to fit a sigmoid curve to the remaining data to determine EC50. Instead, we have applied a mathematical modeling approach to interpret the full dose–response curve in a new way. The developed model predicts a non‐steady‐state caused by a short resting time between increased concentrations of agonist, which affect the dose–response characterization. Therefore, an improved estimate of EC50 may be calculated using steady‐state simulations of the model. The model‐based estimation of EC50 is further refined using additional time‐resolved data to decrease the uncertainty of the prediction. The resulting model‐based EC50 (180–525 nm) is higher than the classically interpreted EC50 (46–191 nm). Mathematical modeling thus makes it possible to re‐interpret previously obtained datasets, and to make accurate estimates of EC50 even when steady‐state measurements are not experimentally feasible.

In situ cardiac perfusion reveals interspecific variation of intraventricular flow separation in reptiles

ABSTRACT The ventricles of non-crocodilian reptiles are incompletely divided and provide an opportunity for mixing of oxygen-poor blood and oxygen-rich blood (intracardiac shunting). However, both cardiac morphology and in vivo shunting patterns exhibit considerable interspecific variation within reptiles. In the present study, we develop an in situ double-perfused heart approach to characterise the propensity and capacity for shunting in five reptile species: the turtle Trachemys scripta, the rock python Python sebae, the yellow anaconda Eunectes notaeus, the varanid lizard Varanus exanthematicus and the bearded dragon Pogona vitticeps. To simulate changes in vascular bed resistance, pulmonary and systemic afterloads were independently manipulated and changes in blood flow distribution amongst the central outflow tracts were monitored. As previously demonstrated in Burmese pythons, rock pythons and varanid lizards exhibited pronounced intraventricular flow separation. As pulmonary or systemic afterload was raised, flow in the respective circulation decreased. However, flow in the other circulation, where afterload was constant, remained stable. This correlates with the convergent evolution of intraventricular pressure separation and the large intraventricular muscular ridge, which compartmentalises the ventricle, in these species. Conversely, in the three other species, the pulmonary and systemic flows were strongly mutually dependent, such that the decrease in pulmonary flow in response to elevated pulmonary afterload resulted in redistribution of perfusate to the systemic circuit (and vice versa). Thus, in these species, the muscular ridge appeared labile and blood could readily transverse the intraventricular cava. We conclude that relatively minor structural differences between non-crocodilian reptiles result in the fundamental changes in cardiac function. Further, our study emphasises that functionally similar intracardiac flow separation evolved independently in lizards (varanids) and snakes (pythons) from an ancestor endowed with the capacity for large intracardiac shunts. Summary: Non-crocodilian reptiles have an undivided ventricle, but some (pythons, varanid lizards) robustly separate blood flow, whereas others (turtles, anacondas, bearded dragons) show a large capacity for cardiac shunting.