Changes in whole blood oxygen affinity and eggshell permeability in high altitude chickens translocated to sea level

High-altitude adaptations in vertebrate hemoglobins

Vertebrates at high altitude are subjected to hypoxic conditions that challenge aerobic metabolism. O(2) transport from the respiratory surfaces to tissues requires matching between the O(2) loading and unloading tensions and the O(2)-affinity of blood, which is an integrated function of hemoglobin's intrinsic O(2)-affinity and its allosteric interaction with cellular effectors (organic phosphates, protons and chloride). Whereas short-term altitudinal adaptations predominantly involve adjustments in allosteric interactions, long-term, genetically-coded adaptations typically involve changes in the structure of the haemoglobin molecules. The latter commonly comprise substitutions of amino acid residues at the effector binding sites, the heme-protein contacts, or at intersubunit contacts that stabilize either the low-affinity ('Tense') or the high-affinity ('Relaxed') structures of the molecules. Molecular heterogeneity (multiple isoHbs with differentiated oxygenation properties) can further broaden the range of physico-chemical conditions where Hb functions under altitudinal hypoxia. This treatise reviews the molecular and cellular mechanisms that adapt haemoglobin-oxygen affinities in mammals, birds and ectothermic vertebrates at high altitude.

Hypoxic adaptations of hemoglobin in Tibetan chick embryo: high oxygen-affinity mutation and selective expression

Tibetan chicks (Gallus gallus) survived with high hatchability (35.0%) and Recessive White Feather broilers (RWF) from low elevations survived rarely and with a low hatchability (3.0%) after simulated incubation under hypoxia of 13% O2. The functional mutation of Met-32D(B13)-Leu of alpha(D) globin chain was related with hypoxia based on allele distribution, homology model building and oxygen affinity assay. Whole embryos on days 3-8 and whole blood on days 9-18 were collected to investigate the stage expression profiles of all seven globins and HIF-1alpha by real-time PCR. Under hypoxia (12.0% O2) on days 3-8, HbE was overexpressed, HbA was expressed earlier and HbP expression was restricted, which completely overturned the expression profile under normoxia. The amount of hemoglobin expression in Tibetan chicks was remarkably higher than that of RWF. HIF-1alpha expression peaked early in both breeds, with. In conclusion, the special hypoxic expression profile on days 3-8 certainly is a common molecular mechanism of hypoxia tolerance in surviving Tibetan chick and RWF embryos; the mutation Met-32D(B13)-Leu and increasing hemoglobins are important mechanisms of hypoxia adaptation in Tibetan chick embryos, and we suggest that HIF-1alpha could be responsible for the hypoxic expression profile.

Hypoxic incubation creates differential morphological effects during specific developmental critical windows in the embryo of the chicken (Gallus gallus)

Hypoxia inhibits vertebrate development, but the magnitude and timing of organ-specific effects are poorly understood. Chick embryos were exposed continuously to hypoxia (15% O2) throughout Days 1-6, 6-12, 12-18 or Days 1-18 of development, followed by morphometric measurements of major organ systems. Early hypoxic exposure reduced eye mass and beak length when measured in middle development. Liver, brain, heart, kidneys, stomach, intestines and skeletal long bones were not affected by hypoxia at any developmental stage. The chorioallantoic membrane (CAM) mass was unchanged by hypoxic exposure in early or mid-development, but CAM mass on Day 18 increased strikingly (40 and 60% in late and continuous populations, respectively) in response to hypoxic exposure. The increase in CAM mass presumably enhances oxygen delivery, thus minimizing the detrimental effects of hypoxia on development and growth. Hypoxic exposure at key critical windows in development thus results in differential effects on organ development, some of which can subsequently be repaired through additional incubation (yolk mass, eye mass, beak length).