Dynamics of acid–base metabolic compensation and hematological regulation interactions in response to CO2 challenges in embryos of the chicken (Gallus gallus)

Acid-base and hematological regulation in chicken embryos during internal progressive hypercapnic hypoxia

Development of the capacity to mitigate potential disturbances to blood physiology in bird embryos is incompletely understood. We investigated regulation of acid-base and hematology in day 15 chicken embryos exposed to graded intrinsic hypercapnic hypoxia created by varying degrees of water submersion. Metabolic acidosis with additional respiratory or metabolic acidosis occurred at 2 h according to magnitude of submersion. Acid-base disturbance was partially compensated by metabolic alkalosis at 6 h, but compensatory metabolic alkalosis was absent at 24 h. Following submersion with only air cell exposed to air, both hypercapnic respiratory acidosis and metabolic acidosis occurred within 10 min. Subsequently, both forms of acidosis created lethal levels of [HCO₃^-] at ∼120 min. Blood hematology showed small but significant effects associated with induced acid-base disturbance. Increased Hct occurring during partial egg submersion lasting 24 h was attributed to an increase in MCV. By day 15 of development chicken embryos are able to partially compensate for and withstand all but severe induced internal hypoxic hypercapnia.

INFLUÊNCIA DOS NÍVEIS DE CO2 E DO TIPO DE INCUBADORA SOBRE O DESEMPENHO ZOOTÉCNICO E MORFOMETRIA CARDÍACA DE FRANGOS DE CORTE

Resumo O objetivo do trabalho foi avaliar incubadoras de estágio múltiplo e único e diferentes níveis de CO2 sobre o desempenho, número e diâmetro das fibras musculares, morfometria cardíaca e rendimento de carcaça de frangos de corte. Foram incubados 2.520 ovos férteis em um delineamento inteiramente ao acaso, distribuídos em quatro níveis de CO2 (4.000, 6.000, 8.000 e 10.000ppm) em incubadoras de estágio único durante os primeiros dez dias de incubação e um tratamento controle utilizando uma incubadora de estágio múltiplo, totalizando cinco tratamentos com 504 ovos em cada um. Após a eclosão, 1.050 pintos machos foram alojados de acordo com o delineamento utilizado no incubatório. A hipercapnia aplicada nos primeiros 10 dias de incubação afetou o ganho de peso e a conversão alimentar dos pintos na primeira semana de vida, no entanto, esses efeitos não foram mantidos até o final do período de criação. Não houve efeito de incubadoras ou da hipercapnia sobre a morfometria muscular e cardíaca. Houve maior rendimento de coxas das aves na idade de abate oriundas de incubadoras em estágio único com até 6.000 ppm de CO2, quando comparadas à incubação em máquinas de estágio múltiplo. Esse efeito pode ser atribuído à maior vascularização induzida pela hipercapnia precoce.

Preferential intracellular pH regulation: hypotheses and perspectives

The regulation of vertebrate acid-base balance during acute episodes of elevated internal PCO2  is typically characterized by extracellular pH (pHe) regulation. Changes in pHe are associated with qualitatively similar changes in intracellular tissue pH (pHi) as the two are typically coupled, referred to as 'coupled pH regulation'. However, not all vertebrates rely on coupled pH regulation; instead, some preferentially regulate pHi against severe and maintained reductions in pHe Preferential pHi regulation has been identified in several adult fish species and an aquatic amphibian, but never in adult amniotes. Recently, common snapping turtles were observed to preferentially regulate pHi during development; the pattern of acid-base regulation in these species shifts from preferential pHi regulation in embryos to coupled pH regulation in adults. In this Commentary, we discuss the hypothesis that preferential pHi regulation may be a general strategy employed by vertebrate embryos in order to maintain acid-base homeostasis during severe acute acid-base disturbances. In adult vertebrates, the retention or loss of preferential pHi regulation may depend on selection pressures associated with the environment inhabited and/or the severity of acid-base regulatory challenges to which they are exposed. We also consider the idea that the retention of preferential pHi regulation into adulthood may have been a key event in vertebrate evolution, with implications for the invasion of freshwater habitats, the evolution of air breathing and the transition of vertebrates from water to land.

Dynamics of blood viscosity regulation during hypoxic challenges in the chicken embryo (Gallus gallus domesticus)

Hypoxia in chicken embryos increases hematocrit (Hct), blood O2 content, and blood viscosity. The latter may limit O2 transport capacity (OTC) via increased peripheral resistance. Hct increase may result from increased nucleated red blood cell concentration ([RBC]) and mean corpuscular volume (MCV) or reduced plasma volume. We hypothesized changes in Hct, hemoglobin concentration ([Hb]), [RBC] and MCV and their effects on viscosity would reduce OTC. Five experimental treatments that increase Hct were conducted on day 15 embryos: 60min water submergence with 60min recovery in air; exposure to 15% O2 with or without 5% CO2 for 24 h with 6 h recovery; or exposure to 10% O2 with or without 5% CO2 for 120 min with 120 min recovery. Control Hct, [Hb], [RBC], MCV, and viscosity were approximately 26%, 9g%, 2.0 10(6)μL(-1), 130μm(3), and 1.6mPas, respectively. All manipulations increased Hct and blood viscosity without changing blood osmolality (276mmolkg(-1)). Increased viscosity was attributed to increased [RBC] and MCV in submerged embryos, but solely MCV in embryos experiencing 10% O2 regardless of CO2. Blood viscosity in embryos exposed to 15% O2 increased via increased MCV alone, and viscosity was constant during recovery despite increased [RBC]. Consequently, blood viscosity was governed by MCV and [RBC] during submergence, while MCV was the strongest determinant of blood viscosity in extrinsic hypoxia with or without hypercapnia. Increased Hct and blood O2 content did not compensate for the effect of increased viscosity on OTC during these challenges.