Hypoxic control of the development of the surfactant system in the chicken: evidence for physiological heterokairy

Abstract

The surfactant system, a complex mixture of lipids and proteins, controls surface tension in the lung and is crucial for the first breath at birth, and thereafter. Heterokairy is defined as plasticity of a developmental process within an individual. Here, we provide experimental evidence for the concept of heterokairy, as hypoxia induces a change in the onset and rate of development of surfactant, probably via endogenous glucocorticoids, to produce individuals capable of surviving early hatching. Chicken eggs were incubated under normoxic (21% O(2)) conditions throughout or under hypoxic (17% O(2)) conditions from day 10 of incubation. Embryos were sampled at days 16, 18, and 20 and also 24 h after hatching. In a second experiment, dexamethasone (Dex), tri-iodothyronine (T(3)), or a combination (Dex + T(3)) was administered 24 and 48 h before each time point. Both hypoxia and Dex accelerated maturation of the surfactant lipids by increasing total phospholipid (PL), disaturated phospholipid (DSP), and cholesterol (Chol) in lavage at days 16 and 18. Maturation of surfactant lipid composition was accelerated, with day 16 %DSP/PL, Chol/DSP, and Chol/PL resembling the ratios of day 20 control animals. The effect of Dex + T(3) was similar to that of Dex alone. Hypoxia increased plasma corticosterone levels at day 16, while plasma T(3) levels were not affected. Hence, exposure to hypoxia during critical developmental windows accelerates surfactant maturation, probably by increasing corticosterone production. This internal modulation of the developmental response to an external stimulus is a demonstration of physiological heterokairy.

Ventilatory chemosensitivity of the 1-day-old chicken hatchling after embryonic hypoxia

“…There are no indications that embryonic hypoxia hinders the surfactant system; on the contrary, in the chicken embryo hypoxia accelerates the maturation of surfactant, possibly through increased corticosterone production (4).…”

Ascites Syndrome in Broiler Chickens: A Review on the Aspect of Endogenous and Exogenous Factors Interactions

“…Alternatively, it could be related to the duration of the hypoxic period and, therefore, to the pipping and hatching time. Blacker et al (2004) provided evidence for the role of hypoxia during the embryonic development regarding the control of pulmonary surfactant. The authors suggested that the avian pulmonary surfactant system exhibits a high level of plasticity within the early stages of surfactant maturation.…”

“…The authors suggested that the avian pulmonary surfactant system exhibits a high level of plasticity within the early stages of surfactant maturation. A possible explanation for these observations is an interaction between environmental and endogenous physiological factors, such as corticosterone and thyroid hormones, during the critical developmental period of chick embryos (Hassanzadeh et al, 2004, Blacker et al, 2004. These interactions could exploit developmental plasticity, which result in the physiological heterokairy of the surfactant system by altering both the rate and onset of production of surfactant lipids and the earlier commencement of air breathing.…”

Higher levels of CO2during late incubation alter the hatch time of chicken embryos

“…This is accordance with the results of previous studies. To achieve a delay and short hatch 204 window, increasing CO2 during incubation can stimulate corticosterone secretion (Blacker et al, 2004).…”